Description of Daphnia: habitat, reproduction and lifestyle of the crustacean. Genus: Daphnia = Daphnia Development cycle of Daphnia

Most often, daphnia is found in stagnant bodies of water - puddles, ponds, lakes, ditches, pits with water. Their massive quantity, suitable for independent preparation, can be detected by the coloring of the water red or gray-green. They feed on bacteria, ciliates and plant plankton, creating a flow of water using the movement of antennas.

When catching daphnia yourself, you need to take into account that they react strongly to lighting. When strong, they will tend to go deeper into the water, and when weak, upward or towards the light source.

Daphnia magna - larva about 0.7 mm, males 2 mm, females up to 6 mm. They ripen in 4-14 days. They produce up to 20 litters every 12-14 days. There are up to 80 eggs in a clutch. Life expectancy is 120 - 150 days. Cerio Daphnia reticulata - larva about 0.3 mm, males 0.5 - 0.8 mm, females up to 1.5 mm, mature in 2 - 3 days. They produce up to 15 litters every 1 - 3 days. There are up to 22 eggs in a clutch.

Life expectancy is 30 days. Moina rectirostris - larva about 0.5 mm, males up to 1 mm, females up to 1.7 mm. Ripen in 3 - 4 days. They produce up to 7 litters every 1 - 2 days. There are up to 53 eggs in a clutch. Life expectancy is 22 days.

Optimum conditions: dH 6-18 o, pH 7.2-8.0, temperature - 20 - 24 o C, CO2 up to 8 mg/l, weak aeration, light 14-16 hours a day. Under conditions of artificial breeding, crustaceans tolerate mineral fertilizers well (for example, up to 5 mg/l of phosphorus salts). They are fed daily with chlorella (200 thousand cells/ml) or baker's yeast (2 ml of suspension per 1 liter of water). You can use horse manure: 1.5 g/l, adding another 0.8 g/l every 10 days. In nature, the food spectrum is wider - green algae (endorina, angistrodesmus, etc.), bacteria.

Kinds

In the middle zone, the following types of daphnia crustaceans are most often found:
the largest Daphnia magna - female size up to 6 mm, male up to 2 mm, larva 0.7 mm, grows within 4-14 days, breeding interval 12-14 days, up to 80 eggs in one clutch, lives 110-150 days;
crustaceans average size, Daphnia pulex, female up to 3-4 mm, breeding period 3-5 days, clutch up to 25 eggs, lives 26-47 days.
small crustaceans, up to 1.5 mm: species of the moina genera, female up to 1.5 mm, male daphnia up to 1.1 mm, daphnia larva 0.5 mm, matures within 24 hours, litters every 1-2 days, up to 7 litters , up to 53 eggs, lives 22 days.

The stomach of freshly caught or freshly frozen Daphnia crustaceans is usually full plant foods, therefore they are useful for feeding aquarium fish deprived of a natural diet.

The shell of daphnia, consisting mainly of chitin, is not digested, but nevertheless serves as a valuable ballast substance that activates the intestinal function of fish that are deprived of the opportunity to actively move in the aquarium. The smallest Daphnia moina, having popular name Daphnia “live-bearer”, well suited for feeding grown juvenile aquarium fish.

Only Daphnia magna, Daphnia pulex, Daphnia mion can be bred by amateurs. But they also need care, proper maintenance, and nutrition. In this case, daphnia will fully reproduce and grow to become high-quality food for fish.

Finding daphnia for home keeping is not difficult: you can buy it or collect it from a pond. Ponds with waterfowl, lakes where there are few or no fish (both daphnia and diseases will be caught with the fish), containers with settled water. The spoils at home are poured into a flat vessel, preferably white. This makes it more convenient to filter the future feed again, because... foreign organisms will settle to the bottom or attach to the white walls, where they are clearly visible.

If the collected crustaceans are used as food for fish, the water in which the live food lives is not poured into a common reservoir. Daphnia are selected with a net so as not to infect aquarium inhabitants. Daphnia Representatives of Cladocerans are kept in a shaded place, because They do not tolerate light well. Normal water temperature for life is in the range from 20 to 24° C (for the species Daphnia moin – 26-27° C), aeration is moderate to weak.

Plankton is fed: diluted baker's yeast, red meat water (meat juice, water washed off from it), chlorella. Yeast is frozen until brownish, in 1 liter warm water dilute 3 grams. yeast; this is the standard proportion. Meat water is given from 0.5 to 2 cm3 per liter of water. Instead of pure chlorella, you can simply add green aquarium water. To ensure that the fish have high-quality food, horse manure and ammonium nitrate are added to the food.

How to breed daphnia at home?

A 15 liter plastic container or any other is perfect for growing daphnia. In this case, several recommendations can be noted: 1. It is necessary to avoid container materials that are soluble in water and emit harmful chemical substances(some types of plastic, in particular polypropylene);

2. If a metal container is used, it should not be made of stainless steel (some metals react slowly with water. Aluminum oxides form an oxide film, but some aluminum is released); 3. As in the case of a regular aquarium, a large surface area with air is required for gas exchange, because daphnia are very demanding of oxygen content;

4. If the container is located outdoors in strong sunlight or other lighting, it is recommended to use more than 40 liter volumes to make the water environment more stable. Additionally, when black aquarium material is used, it will heat up more than clear or yellow material, which should also be taken into account. For those who wish to have a small number of daphnia per week, the culture can be maintained in a two-liter bottle.

A good idea for growing daphnia in an aquarium is to connect the lighting via a timer, which can be purchased at an electrical supply store. It was found that Daphnia magna prefers weak aeration. In theory, aeration not only supports gas exchange, but also stabilizes water conditions and prevents inhibition of cultural development.

Daphnia pulex also likes light aeration. It is necessary to avoid small air bubbles that can get under the Daphnia carapace, raise them to the surface, interfere with feeding and ultimately lead to death (Artemia nauplii are also susceptible to this problem).

Catching

It all depends on the geographical location of the aquarist. The easiest to find are the most common Daphnia pulex and magna. For catching, it is necessary to choose lakes and ponds free of fish, because in the absence of the latter, more daphnia will be observed (due to the lack of predators) and, in addition, the absence of pathogens is guaranteed.

If the aquarist intends to catch daphnia from natural bodies of water, it is advisable to use a fine-mesh net or sieve (homemade from muslin fabric). Pass the net through the water evenly in a figure-eight motion, or scoop it up slowly. Do not allow the net cells to be too small and the water pressure to be too strong when catching, as this can lead to the death of the crustaceans.

Structure

A little more about the structure of daphnia. Aquarists use this name for various cladocerans. You can get an idea of ​​their appearance in the photo. In all representatives of daphnia, the body is strongly compressed laterally and covered with a chitinous bivalve shell fastened on the back. There are two eyes on the head, which in mature individuals can merge into one compound eye, and in some species there may be another additional ocellus next to it.

Also on the head there are two pairs of so-called antennas, the rear of which are large and additionally equipped with bristles that increase their area. It is due to the flapping of these antennas that daphnia move in the water. When stroked by the antennae, the body of the crustacean receives a spasmodic forward movement, for which daphnia received the second, popular name “water flea”.

Daphnia reproduces quite unusually from a human point of view. Female Daphnia have a cavity called the "brood chamber" located on their back and protected by the upper edge of their shell. In the summer, if conditions are favorable, unfertilized eggs are laid in this cavity, in the amount of 50-100 pieces. That's where they develop. Only females hatch from them and leave the chamber, and the adult female then molts.

A few days later the process is repeated. During this time, young female daphnia also grow up and become involved in the reproduction process. With a successful combination of circumstances, reproduction proceeds like an avalanche. This is why in summer, small bodies of water are often swarmed with daphnia, and the water appears reddish in color.

With a decrease in air temperature, at the end of summer and at the beginning of autumn, males begin to emerge from some of the eggs, they fertilize the females and they have eggs enclosed in a dense shell. They are called ephippia. They are able to withstand drying and winter frosts, can spread with dust. Next spring, warmth and moisture will awaken them to life. They will hatch into females and the cycle will repeat.

Many of us enjoy watching the random movement of fish in an aquarium. This sight is soothing and relaxing, but few people know how troublesome it actually is to maintain a house of such beauty.

Fish food

For many decades, pet fish lovers have been using daphnia as food for their aquarium pets. Even in Soviet times, these small crustaceans were caught by aquarists in natural reservoirs. It is clear that they had to know exactly where daphnia lives. Then the caught crustaceans were used not only live, but also frozen and dried. Of course, it is quite difficult to keep a large number of them at home, which is why many try to freeze daphnia during the period of its mass reproduction in nature. If we talk about the nutritional value of frozen food, it is practically in no way inferior to live crustaceans. Nowadays you can easily purchase frozen daphnia in pet stores, so such independent preparation is becoming a relic of the past.

Daphnia structure

I would like to talk a little about how these cladoceran crustaceans, which we call daphnia, work. Their body is quite strongly compressed from the sides, the latter are covered with a two-leaf chitinous shell.

Usually daphnia have two eyes, which are located on the head, but sometimes mature individuals are distinguished by the presence of one compound eye, next to which there may be an additional small eye. There are also two pairs of antennas on the small head. The rear (second) pair is equipped with additional bristles and is large in size. It is thanks to the stroke of these antennae that daphnia make a kind of leap when moving. Therefore, people also call them “water fleas.”

Reproduction of crustaceans

If you look at the process of reproduction of these tiny crustaceans from a human point of view, it is very unusual. Females of this species have a so-called brood chamber, which is reliably protected by the edge of the shell and located on the back. When favorable conditions are created around, the female lays 50-100 unfertilized eggs in this cavity, where they develop. It is curious that only females hatch from these eggs and safely leave the chamber. After just a few days, the process repeats again, and young, grown and mature females will join this rapid reproduction process. That is why in summer, where daphnia lives, the water seems to turn reddish. The reservoir is simply teeming with this plankton. When the end of summer comes, the air and water temperatures drop, males appear and fertilize females, which produce eggs with a denser shell. These are called ephippia. Their distinctive feature is the ability to withstand winter frosts and drying out of water bodies, and they can be spread with dust. With the onset of spring and warmth, females hatch from them, and the process repeats again.

Habitat

After we have learned what daphnia is, the habitat of these representatives of the planktonic genus should also become known to us, because probably many of those who read this article are lovers of pet fish and want to have such information. So, you can find these tiny crustaceans in stagnant bodies of water, for example, lakes, ponds, as well as water holes, ditches and even puddles. Often, places where they gather in large numbers are ideal for harvesting daphnia yourself. You can identify such a place quite easily: where daphnia lives, the water most often has a gray-green or reddish tint. Their food consists of ciliates, bacteria, and plant plankton.

Such different daphnia

Those wishing to catch daphnia themselves must take into account how sensitive they are to light. In bright light, crustaceans will try to go deeper. There are different types of Daphnia. The most common crustacean found in the middle zone is Daphnia magna. The female reaches a length of 6 mm, but the male is only 2 mm. They usually live 110-150 days and in one clutch they produce up to 80 eggs, which grow within 4-14 days. The smallest crustaceans reach only 1.5 mm in size and mature within 24 hours, but they have litters every 1-2 days, up to 53 eggs.

How are they good for fish?

Why do aquarium fish lovers always try to feed them daphnia? Everything is very simple. Regardless of whether these crustaceans are freshly frozen or freshly caught, their stomach is usually full of plant food, and this is so useful for aquarium fish that are deprived of a natural diet. This is why daphnia must be present in the aquarium. Despite the fact that the daphnia shell is not digestible, it serves as an excellent digestion. Thanks to it, the intestines of the fish are activated, which is not able to fully move in the aquarium. For aquarium fish that have not yet grown up, representatives of the smallest daphnia - moina, popularly called "live-bearer" - are simply ideal.

If you plan to catch crustaceans yourself, you must take into account that where daphnia lives, there is a consistent change in the population of crustaceans. For fishing, a fabric net is used, the cells of which must correspond to the desired catch. Some experienced “fishermen” advise fishing with a net with very small cells, and only then sorting the food by size through a sieve with different cells. You can fish starting in spring until a crust of ice appears on the reservoir. For such an event, a coast protected from the wind is usually chosen in calm weather in the morning or evening. It is ideal if the lighting is dim. Then daphnia, the habitat for which will thus become favorable, will rise to the upper layers.

Advice from experienced people

Breeding Daphnia

Breeding daphnia at home is a fairly simple task, but it requires care and patience. For this purpose, baker's yeast is usually used as food. You need to focus on the container where you breed crustaceans. The water should be greenish or light brown. If you notice that its color is becoming saturated, then you need to stop adding yeast for 1-2 days. Very soon the water should brighten again.

If breeding daphnia seems to you a very pleasant and interesting activity, be very careful and make sure that other inhabitants of reservoirs do not get into the vessel along with the crustaceans, especially cyclops. Get a magnifying glass and inspect the females' brood chambers every day. If they contain few eggs, then it is necessary to increase nutrition. Daphnia, whose home habitat is an aquarium or temporary container of water, can also feed on dried nettle or lettuce leaves. They are first ground into powder and then filtered through cheesecloth.

There is another simple way to breed daphnia at home. For this painstaking task, you will need a plastic or enamel bath, which must be half filled with water, and half-rotten hay and fallen leaves must be placed in it. Next, bacteria will begin to develop in this mass, which will become food for the crustaceans. Sometimes, in order to provide additional nutrition to the bacteria, a small piece of yeast is added to the water (approximately 15 g per 1 m 3 of water). This should be done every two weeks as the water becomes lighter.

And now the most important point: daphnia, whose habitat is usually a natural body of water, should end up in your vessel with the prepared food. To do this, 50 crustaceans are caught in about 100 liters of water in a standing reservoir and poured into a prepared container.

Herbst, 1968

Daphnia hispanica Glagolev et Alonso, 1990

Daphnia hyalina Leydig, 1860

Daphnia jollyi Petkovski, 1973

Daphnia lacustris G.O. Sars, 1862

Daphnia laevis Birge, 1879

Daphnia latispina Korinek and Hebert, 1996

Daphnia longiremis G. O. Sars, 1862

Daphnia longispina O. F. Mueller, 1785)

Daphnia lumholtzi G. O. Sars, 1885

Daphnia magna Straus, 1820

Daphnia magniceps Herrick, 1884

Daphnia mediterranea Alonso, 1985

Daphnia menucoensis Paggi, 1996

Daphnia middendorffiana Fischer, 1851

Daphnia minnehaha Herrick, 1884

Daphnia nivalis Hebert, 1977

Daphnia occidentalis Benzie, 1986

Daphnia obtusa Kurz, 1875

Daphnia oregonensis Korinek and Hebert, 1996

Daphnia pamirensis Rylov, 1928

Daphnia parvula Fordyce, 1901

Daphnia peruviana Harding, 1955

Daphnia pileata Hebert and Finston, 1996

Daphnia prolata Hebert and Finston, 1996

Daphnia psittacea Baird, 1850

Daphnia pulex Leydig, 1860)

Daphnia pulicaria Forbes, 1893

Daphnia pusilla (Serventy, 1929)

Daphnia retrocurva Forbes, 1882

Daphnia quadrangula (Sergeev, 1990)

Daphnia queenslandensis (Sergeev, 1990)

Daphnia rosea G. O. Sars, 1862

Daphnia salina Hebert and Finston, 1993

Daphnia schoedleri G. O. Sars, 1862

Daphnia similis Claus, 1876

Daphnia similoides Hudec, 1991

Daphnia sinevi Kotov, Ishida et Taylor, 2006

Daphnia stuederi (Ruhe, 1914)

Daphnia tanakai Ishida, Kotov et Taylor, 2006

Daphnia tenebrosa G. O. Sars, 1898

Daphnia tibetana (G.O. Sars, 1903)

Daphnia thomsoni G.O. Sars, 1894

Daphnia thorata Forbes, 1893

Daphnia triquetra G.O. Sars, 1903

Daphnia truncata Hebert and Wilson, 2000

Daphnia turbinata G.O.Sars, 1903

Daphnia umbra

Daphnia villosa Korinek and Hebert, 1996

Daphnia wardi Hebert and Wilson, 2000

External structure

Unless otherwise stated, this section describes the anatomy of females. The integument consists of a head shield and a bivalve carapace. Usually they have a clearly visible pattern of rhombuses and polygons - reticulation. Each such cell of the integument is formed by one cell of the hypodermis. There are spines at the edge of the valves, and at the posterior end there is a tail spine covered with spines. Many species have a row of feathered setae on the inner edge of the valves in its middle part; males of all species have the same setae and additional setae on the anterior-inferior corner of the valves.

On the head of most species, a beak-like outgrowth is developed - the rostrum. Below it are located the first antennae (antennales) - short projections bearing at the end 9 olfactory setae - aesthetascus (aesthetascus), and on the lateral surface - one additional seta. In males, the first antennae are larger, more mobile, and, in addition to aesthetascae, bear a large seta (“flagellum”) at the distal end.

On the lateral surface of the head there are projections of the cuticle - fornixes. Their shape, as well as the shape of the posterior edge of the head shield, is an important diagnostic feature of subgenera and groups of species. Under the fornix, second antennae (antennae) are attached to the head by a complex “joint”. They consist of a base and two branches - an internal three-segmented and an external four-segmented. At the ends of the segments of the branches there are two-segmented swimming setae covered with flattened hairs, forming “oars” when swimming. There are five of them on the three-segmented branch (four only in D. cristata), on a four-segmented one - four. There are several small sensitive bristles on the base.

From back surface a large upper lip comes off the head. Inside it there are several giant polyploid cells that secrete a secretion that glues the food into a food bolus.

On the border between the head shield and the carapace, mandibles are located under the valves. They have a complex shape, are asymmetrical and have highly chitinized chewing surfaces covered with ridges and outgrowths. During feeding, the mandibles transport food into the mouth opening.

Under the carapace there are small maxillae 1 (maxillulae), bearing four setae. The second maxillae in Daphnia are reduced. There are five pairs of two-branched thoracic legs of complex structure. The legs of the first and partly the second pair differ in structure in males and females. On the first pair of legs of males there are hook-shaped projections that allow them to cling to females during mating. The third and fourth pairs carry fans of filter bristles. Each leg has a respiratory appendage - an epipodite.

Behind the thoracic region there is a reduced abdominal region, the presence of which is “marked” by dorsal abdominal processes that cover the exit from the brood chamber. There are usually four of them, they are well developed in mature females and reduced in males of most species.

The posterior part of the body is a large mobile post-abdomen, homologous to the telson of other crustaceans. On its dorsal side there are two rows of denticles, between which is the anus. In males of some species these denticles are partially or completely reduced. At the end of the postabdomen there are paired claws covered with spines. According to some data, they are homologous to the furca, according to others, they are a pair of large modified setae. There are spines on the outer and inner sides of the claws; usually there are three groups of spines on the outer side and two on the inner side. The post-domain serves to clean the filtration apparatus from large foreign particles.

Internal structure

The integumentary system of daphnia is represented by a typical hypodermis. The hypodermis of the carpax consists of large cells forming rhombic-shaped cells.

The central nervous system consists of the suprapharyngeal ganglion (brain) and the ventral nerve cord with several paired ganglia. The brain is clearly visible in living individuals, which is extremely rare. It consists of a large, bisected optic ganglion and the suprapharyngeal ganglion proper. The optic nerve arises from the anterior part of the optic ganglion and connects the brain to the compound eye. The unpaired compound eye in Daphnia is formed from a paired rudiment (embryos have two eyes) and contains exactly 22 facets (ommatidium). It is located in a special cavity inside the head, to the walls of which it is suspended by two ligaments (ligaments) and driven by three pairs of extraocular muscles. In living individuals, tremor of the eye is noticeable, and from time to time larger jumps (saccades) of the eye are observed. Nerves also extend from the brain to the ocellus (simple eye), the first antennae (at their base there is a sensitive ganglion, the cells of which innervate the olfactory bristles - aesthetes), as well as nerves to the sensitive occipital organ of unknown purpose. Adjacent to the lower part of the suprapharyngeal ganglion is the simple eye (ocelli, nauplial eye). In most species it contains pigment and is visible as a small blackhead. There are 4 groups of sensitive cells around the pigment spot.

Daphnia has a complex system of striated muscles that move the second antennae, post-abdomen and thoracic limbs, as well as muscles that move the eyes, upper lip, etc. The muscles of the digestive tract are also striated.

The digestive tract begins with the oral opening, which is covered by a large upper lip. Giant highly polyploid cells located inside the lip secrete a secretion that glues food into a food bolus. Through the movements of the mandibles, it is transported into the thin esophagus, the dilator muscles of which create peristalsis, ensuring the transport of food through the esophagus. Inside the head, the esophagus passes into the wider midgut, which extends to the middle part of the post-abdomen. Inside the head, two curved liver processes extend from the midgut. In the posterior part of the post-abdomen there is a short hindgut.

The heart is located on the dorsal side of the body, in front of the edge of the brood chamber. Blood (hemolymph), the flow of which is clearly visible due to the presence of colorless cells in it - phagocytes, enters the heart through the ostia - two slit-like side openings. When the heart contracts, the ostia close with valves, and blood is ejected through the anterior opening to the head. There are no blood vessels; the regular direction of blood flow is ensured by transparent partitions between different parts of the myxocoel.

Breathing occurs through the integument of the body, primarily the thoracic legs, on which there are respiratory appendages - epipodites. The latter also take part in osmoregulation. An additional organ of osmoregulation in newborns is the large nuchal pore (occipital organ), which disappears after the first postembryonic molt.

The excretory organs are complex-shaped maxillary glands, which are located on the inner surface of the valves in their anterior part.

Paired ovaries (testes in males) are located on the sides of the intestines. At the posterior end there is a breeding zone for oogonia; the rest of the ovary is filled with maturing oocytes. As the eggs mature, they move to their posterior third, where there are narrow oviducts that open into the brood chamber. In males, the vas deferens open on the postabdomen in its distal part, and in many species on special papillae.

Shedding

When molting, the cervical suture, the line between the head shield and the carapace, separates, and the animal emerges from the exuvium. Together with the carapace, the integument of the body and limbs is shed. Molting occurs periodically throughout the life of the individual. Typically, molting occurs in the water column; ephippial females of some species molt, sticking from below to the surface film of the water. Several molts occur during embryonic development, in the brood chamber.

Spreading

Genus Daphnia has a worldwide distribution (including Antarctica, where in the relict salt lakes of the Vestfold oasis ( Westfold Hills) was found Daphnia studeri, previously classified as a genus Daphniopsis). At the beginning of the 20th century, the prevailing opinion was that most species had a cosmopolitan distribution, but it later became clear that the faunas of different continents differ greatly. Some species, however, have very wide ranges and are distributed on several continents. The smallest number of species is typical for equatorial regions, where daphnia are rare. The most diverse fauna is in the subtropics and temperate latitudes. In recent decades, the ranges of many species have changed due to human dispersal. Thus, a species from the New World was introduced into Europe (England) D.ambigua. It has become common in many reservoirs in the southern United States. D. lumholtzi, which was previously found only in the Old World.

In ponds and puddles middle zone In Russia, the following crustaceans of the genus Daphnia are often found (and most popular among aquarists):

Daphnia magna (D. magna), female - up to 6 mm, male - up to 2 mm, newborns - 0.7 mm. They ripen within 10-14 days. Litters in 12-14 days. There are up to 80 eggs in a clutch (usually 20-30). Life expectancy is up to 3 months.

Daphnia pulex (D. pulex), female - up to 3-4 mm, male - 1-2 mm. Litters in 3-5 days. There are up to 25 eggs in a clutch (usually 10-12). They live 26-47 days.

In lakes of the temperate zone of Eurasia they are often found D. cucullata, D. galeata, D. cristata and several other types.

Biology

Daphnia are small crustaceans (the body size of adults is from 0.6 to 6 mm). They inhabit all types of standing continental bodies of water and are also found in many slow-flowing rivers. In puddles, ponds and lakes they often have high numbers and biomass. Daphnia are typical planktonic crustaceans, spending most of their time in the water column. Various species inhabit shallow temporary reservoirs. littoral and pelagic zones of lakes. Quite a few species, especially those inhabiting arid areas, are halophiles, living in brackish, saline and hypersaline continental water bodies. These types include, for example, D. magna, D. atkinsoni, D.mediterranea, as well as most species previously classified in the genus Daphniopsis.

Locomotion

They spend most of their time in the water column, moving in sharp leaps due to the flapping of the second antennae, which are covered with special feathered bristles (hence their common name - “water fleas,” often applied to all cladocerans). Many daphnia are also capable of slowly crawling along the bottom or walls of vessels due to water currents created by the thoracic legs (the antennae are motionless with this method of movement).

Nutrition

The main food for daphnia are bacteria and unicellular algae. Species that survive the winter in an active state (in deep, non-freezing reservoirs) spend it in the bottom layers of water, feeding mainly on detritus. They feed by filtration, creating currents of water with rhythmic movements of the chest legs. Food is filtered by fans of filtering setae, which are located on the endopodites of the III and IV pairs of thoracic legs. Large particles stuck in the filtration apparatus (for example, filamentous algae) are removed using the postabdomen and its claws. From the filtering fans, food enters the abdominal food groove, is transmitted to the maxillae of the first pair and then to the mandibles, the movements of which transport it to the esophagus. In front, the mouth opening of daphnia is covered with a large upper lip, inside of which there are salivary glands made of giant polyploid cells. Their secretion glues food particles together into a food bolus.

At an average concentration of food in water, adult daphnia of various species are filtered at a rate of 1 to 10 ml/day. Daily food intake for adults D. magna can reach 600% of her body weight.

Gas exchange

On the thoracic legs there are sac-like respiratory appendages - gills. Probably, a significant part of the oxygen of daphnia is obtained through the thin integument of the body and limbs, and the respiratory appendages, like the occipital organ of newborns, play important role in osmoregulation. Some types (for example, D. pulex, D. magna) with a low oxygen content in the water, they begin to synthesize hemoglobin, so that their hemolymph and the whole body turns red.

Cyclomorphosis

Many species of daphnia (mainly living in lakes) exhibit cyclomorphosis - their different generations, developing in different seasons of the year, differ sharply in body shape. In temperate latitudes, summer generations of such species have elongated cuticle outgrowths - a tail spine and a head shield. In spring and autumn generations, the tail spine is shorter, the helmet may be shorter or absent altogether. It has been shown that growing outgrowths requires energy expenditure and leads to a decrease in fertility. Among the factors causing the growth of outgrowths of the integument, the influence of increased water turbulence, high temperature, etc. was demonstrated. Later it was shown that the main influence on the growth of cyclomorphic outgrowths is exerted by kairomones - signaling substances secreted by different types of invertebrate and vertebrate predators. Many hypotheses have been put forward about the adaptive role of cyclomorphosis: easier soaring in less dense and viscous water, accelerated swimming in the horizontal direction, etc. Most of them are either unproven or refuted. Nowadays, the theory about the role of outgrowths in protection from predators is accepted as the main explanation for cyclomorphosis. Transparent outgrowths increase the actual size of the body and thereby protect against small invertebrate predators - larger prey with outgrowths are more difficult to grab and not release during manipulation - “stuffing into the mouth.” Sometimes the tail spine breaks off, which can play the same role as autotomy of the tail in a lizard. At the same time, transparent outgrowths do not increase the apparent size, which is important for protection from large visual predators - fish.

Vertical migrations

During the period of bisexual reproduction, some females give birth to males, while others at the same time form resting, or ephippial, eggs. They are formed by meiosis and require fertilization to develop. After fertilization, they also exit into the brood chamber, the covers of which thicken and form a special chitinous chamber - the ephippium (ephippium). Most Daphnia species have two eggs in the ephippium; in some Australian species, often classified as a separate genus Daphniopsis, there is one egg in the ephippium. In species of the subgenus Daphnia the long axes of the eggs are perpendicular to the dorsal margin of the ephippium, in species of the subgenus Ctenodaphnia- parallel to it or inclined at a slight angle. Egg development continues until the gastrula stage, after which they enter suspended animation. During the next molt, the female sheds the ephippium, which in some species usually sinks to the bottom, while in others it floats on the surface of the reservoir. When laying effipium, females of some species (for example, D. pulex) often die. Together with ephippiums, daphnia eggs are carried by the wind, spreading on the paws of mammals, on the paws and feathers of birds, as well as in their intestines. It has also been shown that floating ephippiums can stick to the body of smooth bugs taking off from the surface of the water and be carried by them, and more often smooth ephippiums are carried by smaller ephippiums. Eggs in a chemically resistant shell inside the ephippium can remain viable after passing through the intestines of birds and fish. They usually also withstand freezing and prolonged drying. It has been shown that resting daphnia eggs can survive and develop for a long time in solutions of toxic salts (for example,) at a concentration of poisons thousands of times higher than the maximum permissible concentration; after the egg shell ruptures, the hatched embryos in such solutions immediately die.

Use in scientific research

Daphnia are used as model organisms in many ecological, toxicological and genetic studies.

Decoding the genome

In recent years, the Daphnia genome has been partially deciphered Daphnia pulex, its draft was completed in 2011. The Daphnia genome consists of 200 million nucleotides, but it contains at least 30.9 thousand genes - more than other multicellular animals that have been studied so far (for example, the human genome has about 20-25 thousand genes). The Daphnia genome was characterized by a high rate of gene duplications, which led to the creation of numerous gene clusters. More than a third of the gene products found in the Daphnia genome have no known homologs in the proteomes of other organisms. The largest amplified gene families are also characteristic only of this evolutionary line. Many paralog genes are expressed differently depending on environmental conditions; genes unique to daphnia are most sensitive to changes in conditions. It can be assumed that gene duplications increased the ecological plasticity of daphnia, allowing them to adapt to the conditions of different reservoirs and to changing conditions in the same reservoir.

Breeding

Cultivation of Daphnia as food is widespread, as in industrial purposes, and by amateur aquarists. In favorable conditions, daphnia reproduce and grow easily and quickly, which makes it possible to obtain 30-50 (in some cases up to 100) grams of crustaceans per day from one cubic meter of culture.

The source culture can easily be obtained from natural reservoirs. It is advisable to catch crustaceans in small bodies of water, where the daphnia population can be practically free from the admixture of other animals. In winter, a culture of daphnia can be obtained from ephippial resting eggs, previously collected from the surface of the water or from the upper layer of silt. Collected ephippiums are well preserved in a dry state in a cool room.

Depending on the required number of crustaceans, daphnia can be cultivated both in small vessels and in large pools and ponds. The optimal density of the crop is 300-1000 g/m³. Periodically, every few weeks or months, the culture is replanted. The aging of a crop is associated with the accumulation of metabolic and decomposition products in it and with its contamination by other organisms. When changing water, the life of the crop is extended.

The optimal growing temperature is 15-25°C, the medium reaction is neutral (pH 6.8-7.8), oxygen content is at least 3-6 mg/l, oxidability is 14.8-26.2 mg O 2 /l.

When growing daphnia, both joint and separate cultivation of crustaceans and food for them are used.

When grown together, add to the culture organic fertilizers, for example, manure applied in an amount of 1.5 kg/m 3. It is possible to grow on mineral fertilizers, the addition of which causes the rapid development of unicellular algae.

The disadvantages of co-cultivation are severe water pollution, rapid aging of the culture and rapid overgrowing of the container with filamentous algae.

Separate cultivation of daphnia and food for them does not have these disadvantages, but is technically more complex and is used mainly in conditions of mass industrial cultivation of feed crustaceans. In this case, an algal culture is grown separately, which is added to the container with daphnia 1-2 times a day.

In laboratory and home conditions, it is convenient to maintain a culture of daphnia with yeast, added daily little by little in the amount of 15-20 g per cubic meter of culture (15-20 mg/l).. Standardized methods for laboratory culture of Daphnia are described in toxicology and bioassay manuals.

Other facts

Live, dried and frozen daphnia are often used as food for aquarium fish or insects kept in terrariums. In industrial fish farming, breeding daphnia for food is of great importance.

Daphnia is one of the standard objects for testing the toxicity of aqueous solutions of chemical compounds used in the study of aquatic environmental pollution. Daphnia are sensitive even to small concentrations of some salts, for example, the addition of copper salts at a concentration of 0.01 mg/l causes the movements of the crustaceans to slow down, they either sink to the bottom or freeze at the surface film of water.

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Notes

1. // Encyclopedic Dictionary of Brockhaus and Efron: in 86 volumes (82 volumes and 4 additional). - St. Petersburg. , 1890-1907.
2. , With. 119.
3. , With. 123.
4. Keonho Kim, Alexey A Kotov, and Derek J. Taylor. Hormonal induction of undescribed males resolves cryptic species of cladocerans//Proceedings of the Royal Society B: Biological Sciences. 2006 January 22; 273(1583): 141-147.
6. .
7. , With. 555.
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11. , With. 128.
12. , With. 136.
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15. , With. 134.
16. , With. 48.
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18. , With. 103.

Literature

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Links

• - database of genomes of representatives of the genus Daphnia(English) (Retrieved March 5, 2011)

Excerpt characterizing Daphnia

“You can’t dirty Marya Genrikhovna’s dress,” answered the voices.
Rostov and Ilyin hurried to find a corner where they could change their wet dress without disturbing Marya Genrikhovna’s modesty. They went behind the partition to change clothes; but in a small closet, filling it completely, with one candle on an empty box, three officers were sitting, playing cards, and did not want to give up their place for anything. Marya Genrikhovna gave up her skirt for a while to use it instead of a curtain, and behind this curtain Rostov and Ilyin, with the help of Lavrushka, who brought packs, took off the wet dress and put on a dry dress.
A fire was lit in the broken stove. They took out a board and, having supported it on two saddles, covered it with a blanket, took out a samovar, a cellar and half a bottle of rum, and, asking Marya Genrikhovna to be the hostess, everyone crowded around her. Some offered her a clean handkerchief to wipe her lovely hands, some put a Hungarian coat under her feet so that it would not be damp, some curtained the window with a cloak so that it wouldn’t blow, some brushed the flies off her husband’s face so that he would not wake up.
“Leave him alone,” said Marya Genrikhovna, smiling timidly and happily, “he’s already sleeping well after a sleepless night.”
“You can’t, Marya Genrikhovna,” the officer answered, “you have to serve the doctor.” That’s it, maybe he’ll feel sorry for me when he starts cutting my leg or arm.
There were only three glasses; the water was so dirty that it was impossible to decide whether the tea was strong or weak, and in the samovar there was only enough water for six glasses, but it was all the more pleasant, in turn and by seniority, to receive your glass from Marya Genrikhovna’s plump hands with short, not entirely clean, nails . All the officers seemed to really be in love with Marya Genrikhovna that evening. Even those officers who were playing cards behind the partition soon abandoned the game and moved on to the samovar, obeying the general mood of courting Marya Genrikhovna. Marya Genrikhovna, seeing herself surrounded by such brilliant and courteous youth, beamed with happiness, no matter how hard she tried to hide it and no matter how obviously shy she was at every sleepy movement of her husband, who was sleeping behind her.
There was only one spoon, there was most of the sugar, but there was no time to stir it, and therefore it was decided that she would stir the sugar for everyone in turn. Rostov, having received his glass and poured rum into it, asked Marya Genrikhovna to stir it.
- But you don’t have sugar? - she said, still smiling, as if everything that she said, and everything that others said, was very funny and had another meaning.
- Yes, I don’t need sugar, I just want you to stir it with your pen.
Marya Genrikhovna agreed and began to look for a spoon, which someone had already grabbed.
“You finger, Marya Genrikhovna,” said Rostov, “it will be even more pleasant.”
- It's hot! - said Marya Genrikhovna, blushing with pleasure.
Ilyin took a bucket of water and, dripping some rum into it, came to Marya Genrikhovna, asking him to stir it with his finger.
“This is my cup,” he said. - Just put your finger in, I’ll drink it all.
When the samovar was all drunk, Rostov took the cards and offered to play kings with Marya Genrikhovna. They cast lots to decide who would be Marya Genrikhovna's party. The rules of the game, according to Rostov’s proposal, were that the one who would be king would have the right to kiss Marya Genrikhovna’s hand, and that the one who would remain a scoundrel would go and put a new samovar for the doctor when he woke up.
- Well, what if Marya Genrikhovna becomes king? – Ilyin asked.
- She’s already a queen! And her orders are law.
The game had just begun when the doctor’s confused head suddenly rose from behind Marya Genrikhovna. He had not slept for a long time and listened to what was said, and, apparently, did not find anything cheerful, funny or amusing in everything that was said and done. His face was sad and despondent. He did not greet the officers, scratched himself and asked permission to leave, as his way was blocked. As soon as he came out, all the officers burst into loud laughter, and Marya Genrikhovna blushed to tears and thereby became even more attractive in the eyes of all the officers. Returning from the yard, the doctor told his wife (who had stopped smiling so happily and was looking at him, fearfully awaiting the verdict) that the rain had passed and that she had to go spend the night in the tent, otherwise everything would be stolen.
- Yes, I’ll send a messenger... two! - said Rostov. - Come on, doctor.
– I’ll watch the clock myself! - said Ilyin.
“No, gentlemen, you slept well, but I didn’t sleep for two nights,” said the doctor and gloomily sat down next to his wife, waiting for the end of the game.
Looking at the gloomy face of the doctor, looking askance at his wife, the officers became even more cheerful, and many could not help laughing, for which they hastily tried to find plausible excuses. When the doctor left, taking his wife away, and settled into the tent with her, the officers lay down in the tavern, covered with wet overcoats; but they didn’t sleep for a long time, either talking, remembering the doctor’s fright and the doctor’s amusement, or running out onto the porch and reporting what was happening in the tent. Several times Rostov, turning over his head, wanted to fall asleep; but again someone’s remark entertained him, a conversation began again, and again causeless, cheerful, childish laughter was heard.

At three o'clock no one had yet fallen asleep when the sergeant appeared with the order to march to the town of Ostrovne.
With the same chatter and laughter, the officers hastily began to get ready; again they put the samovar on dirty water. But Rostov, without waiting for tea, went to the squadron. It was already dawn; the rain stopped, the clouds dispersed. It was damp and cold, especially in a wet dress. Coming out of the tavern, Rostov and Ilyin, both in the twilight of dawn, looked into the doctor’s leather tent, shiny from the rain, from under the apron of which the doctor’s legs stuck out and in the middle of which the doctor’s cap was visible on the pillow and sleepy breathing could be heard.
- Really, she’s very nice! - Rostov said to Ilyin, who was leaving with him.
- What a beauty this woman is! – Ilyin answered with sixteen-year-old seriousness.
Half an hour later the lined up squadron stood on the road. The command was heard: “Sit down! – the soldiers crossed themselves and began to sit down. Rostov, riding forward, commanded: “March! - and, stretching out into four people, the hussars, sounding the slap of hooves on the wet road, the clanking of sabers and quiet talking, set off along the large road lined with birches, following the infantry and battery walking ahead.
Torn blue-purple clouds, turning red at sunrise, were quickly driven by the wind. It became lighter and lighter. The curly grass that always grows along country roads, still wet from yesterday’s rain, was clearly visible; The hanging branches of the birches, also wet, swayed in the wind and dropped light drops to their sides. The faces of the soldiers became clearer and clearer. Rostov rode with Ilyin, who did not lag behind him, on the side of the road, between a double row of birch trees.
During the campaign, Rostov took the liberty of riding not on a front-line horse, but on a Cossack horse. Both an expert and a hunter, he recently got himself a dashing Don, a large and kind game horse, on which no one had jumped him. Riding this horse was a pleasure for Rostov. He thought about the horse, about the morning, about the doctor, and never thought about the upcoming danger.
Before, Rostov, going into business, was afraid; Now he did not feel the slightest sense of fear. It was not because he was not afraid that he was accustomed to fire (you cannot get used to danger), but because he had learned to control his soul in the face of danger. He was accustomed, when going into business, to think about everything, except for what seemed to be more interesting than anything else - about the upcoming danger. No matter how hard he tried or reproached himself for cowardice during the first period of his service, he could not achieve this; but over the years it has now become natural. He now rode next to Ilyin between the birches, occasionally tearing leaves from branches that came to hand, sometimes touching the horse’s groin with his foot, sometimes, without turning around, giving his finished pipe to the hussar riding behind, with such a calm and carefree look, as if he was riding ride. He felt sorry to look at Ilyin’s agitated face, who spoke a lot and restlessly; he knew from experience the painful state of waiting for fear and death in which the cornet was, and knew that nothing except time would help him.
The sun had just appeared on a clear streak from under the clouds when the wind died down, as if it did not dare spoil this lovely summer morning after the thunderstorm; the drops were still falling, but vertically, and everything became quiet. The sun came out completely, appeared on the horizon and disappeared into a narrow and long cloud standing above it. A few minutes later the sun appeared even brighter on the upper edge of the cloud, breaking its edges. Everything lit up and sparkled. And along with this light, as if answering it, gun shots were heard ahead.
Before Rostov had time to think about and determine how far these shots were, the adjutant of Count Osterman Tolstoy galloped up from Vitebsk with orders to trot along the road.
The squadron drove around the infantry and battery, who were also in a hurry to go faster, went down the mountain and, passing through some empty village without inhabitants, climbed the mountain again. The horses began to lather, the people became flushed.
- Stop, be equal! – the division commander’s command was heard ahead.
- Left shoulder forward, step march! - they commanded from the front.
And the hussars along the line of troops went to the left flank of the position and stood behind our lancers who were in the first line. On the right stood our infantry in a thick column - these were reserves; above it on the mountain, our guns were visible in the clean, clear air, in the morning, oblique and bright light, right on the horizon. Ahead, behind the ravine, enemy columns and cannons were visible. In the ravine we could hear our chain, already engaged and cheerfully clicking with the enemy.
Rostov, as if hearing the sounds of the most cheerful music, felt joy in his soul from these sounds, which had not been heard for a long time. Tap ta ta tap! – several shots clapped suddenly, then quickly one after another. Again everything fell silent, and again it was as if firecrackers were cracking as someone walked on them.
The hussars stood in one place for about an hour. The cannonade began. Count Osterman and his retinue rode behind the squadron, stopped, talked with the regiment commander and rode off to the guns on the mountain.
Following Osterman’s departure, the lancers heard a command:
- Form a column, line up for the attack! “The infantry ahead of them doubled their platoons to let the cavalry through. The lancers set off, their pike weather vanes swaying, and at a trot they went downhill towards the French cavalry, which appeared under the mountain to the left.
As soon as the lancers went down the mountain, the hussars were ordered to move up the mountain, to cover the battery. While the hussars were taking the place of the lancers, distant, missing bullets flew from the chain, squealing and whistling.
This sound, not heard for a long time, had an even more joyful and exciting effect on Rostov than the previous sounds of shooting. He, straightening up, looked at the battlefield opening from the mountain, and with all his soul participated in the movement of the lancers. The lancers came close to the French dragoons, something was tangled there in the smoke, and five minutes later the lancers rushed back not to the place where they stood, but to the left. Between the orange lancers on red horses and behind them, in a large heap, were visible blue French dragoons on gray horses.

Rostov, with his keen hunting eye, was one of the first to see these blue French dragoons pursuing our lancers. Closer and closer the lancers and the French dragoons pursuing them moved in frustrated crowds. One could already see how these people, who seemed small under the mountain, collided, overtook each other and waved their arms or sabers.
Rostov looked at what was happening in front of him as if he were being persecuted. He instinctively felt that if he now attacked the French dragoons with the hussars, they would not resist; but if you hit, you had to do it now, this minute, otherwise it will be too late. He looked around him. The captain, standing next to him, did not take his eyes off the cavalry below in the same way.
“Andrei Sevastyanich,” said Rostov, “we will doubt them...
“It would be a dashing thing,” said the captain, “but in fact...
Rostov, without listening to him, pushed his horse, galloped ahead of the squadron, and before he had time to command the movement, the entire squadron, experiencing the same thing as him, set off after him. Rostov himself did not know how and why he did it. He did all this, as he did on the hunt, without thinking, without thinking. He saw that the dragoons were close, that they were galloping, upset; he knew that they could not stand it, he knew that there was only one minute that would not return if he missed it. The bullets screeched and whistled around him so excitedly, the horse begged forward so eagerly that he could not stand it. He touched his horse, gave the command, and at the same moment, hearing behind him the sound of the stomping of his deployed squadron, at full trot, he began to descend towards the dragoons down the mountain. As soon as they went downhill, their trot gait involuntarily turned into a gallop, which became faster and faster as they approached their lancers and the French dragoons galloping behind them. The dragoons were close. The front ones, seeing the hussars, began to turn back, the rear ones stopped. With the feeling with which he rushed across the wolf, Rostov, releasing his bottom at full speed, galloped across the frustrated ranks of the French dragoons. One lancer stopped, one foot fell to the ground so as not to be crushed, one riderless horse got mixed up with the hussars. Almost all the French dragoons galloped back. Rostov, having chosen one of them on a gray horse, set off after him. On the way he ran into a bush; a good horse carried him over, and, barely able to cope in the saddle, Nikolai saw that in a few moments he would catch up with the enemy whom he had chosen as his target. This Frenchman was probably an officer - judging by his uniform, he was bent over and galloping on his gray horse, urging it on with a saber. A moment later, Rostov’s horse hit the rear of the officer’s horse with its chest, almost knocking it down, and at the same moment Rostov, without knowing why, raised his saber and hit the Frenchman with it.
The instant he did this, all the animation in Rostov suddenly disappeared. The officer fell not so much from the blow of the saber, which only slightly cut his arm above the elbow, but from the push of the horse and from fear. Rostov, holding back his horse, looked for his enemy with his eyes to see whom he had defeated. The French dragoon officer was jumping on the ground with one foot, the other was caught in the stirrup. He, squinting in fear, as if expecting a new blow every second, wrinkled his face and looked up at Rostov with an expression of horror. His face, pale and splattered with dirt, blond, young, with a hole in the chin and light blue eyes, was not the face of a battlefield, not an enemy’s face, but a very simple indoor face. Even before Rostov decided what he would do with him, the officer shouted: “Je me rends!” [I give up!] In a hurry, he wanted and could not untangle his leg from the stirrup and, without taking his frightened blue eyes off, looked at Rostov. The hussars jumped up and freed his leg and put him on the saddle. Hussars from different sides fiddled with the dragoons: one was wounded, but, with his face covered in blood, did not give up his horse; the other, hugging the hussar, sat on the croup of his horse; the third, supported by a hussar, climbed onto his horse. The French infantry ran ahead, shooting. The hussars hastily galloped back with their prisoners. Rostov galloped back with the others, experiencing some kind of unpleasant feeling that squeezed his heart. Something unclear, confusing, which he could not explain to himself, was revealed to him by the capture of this officer and the blow he dealt him.
Count Osterman Tolstoy met the returning hussars, called Rostov, thanked him and said that he would report to the sovereign about his brave deed and would ask for the St. George Cross for him. When Rostov was demanded to appear before Count Osterman, he, remembering that his attack had been launched without orders, was fully convinced that the boss was demanding him in order to punish him for his unauthorized act. Therefore, Osterman’s flattering words and the promise of a reward should have struck Rostov all the more joyfully; but the same unpleasant, unclear feeling sickened him morally. “What the hell is tormenting me? – he asked himself, driving away from the general. - Ilyin? No, he's intact. Have I embarrassed myself in any way? No. Everything is wrong! “Something else tormented him, like remorse.” - Yes, yes, this French officer with a hole. And I remember well how my hand stopped when I raised it.”
Rostov saw the prisoners being taken away and galloped after them to see his Frenchman with a hole in his chin. He, in his strange uniform, sat on a winding hussar horse and restlessly looked around him. The wound on his hand was almost not a wound. He feigned a smile at Rostov and waved his hand as a greeting. Rostov still felt awkward and ashamed of something.
All this day and the next, Rostov's friends and comrades noticed that he was not boring, not angry, but silent, thoughtful and concentrated. He drank reluctantly, tried to remain alone and kept thinking about something.
Rostov kept thinking about this brilliant feat of his, which, to his surprise, bought him the St. George Cross and even made him a reputation as a brave man - and he just couldn’t understand something. “So they are even more afraid of us! - he thought. – So that’s all there is to it, what’s called heroism? And did I do this for the fatherland? And what is he to blame with his hole and blue eyes? And how scared he was! He thought that I would kill him. Why should I kill him? My hand trembled. And they gave me the St. George Cross. Nothing, I don’t understand anything!”
But while Nikolai was processing these questions within himself and still did not give himself a clear account of what had so confused him, the wheel of happiness in his career, as often happens, turned in his favor. He was pushed forward after the Ostrovnensky affair, they gave him a battalion of hussars and, when it was necessary to use a brave officer, they gave him instructions.

Having received the news of Natasha’s illness, the Countess, still not entirely healthy and weak, came to Moscow with Petya and the whole house, and the entire Rostov family moved from Marya Dmitrievna to their own house and completely settled in Moscow.
Natasha’s illness was so serious that, to her happiness and to the happiness of her family, the thought of everything that was the cause of her illness, her action and the break with her fiancé became secondary. She was so sick that it was impossible to think about how much she was to blame for everything that happened, while she did not eat, did not sleep, was noticeably losing weight, was coughing and was, as the doctors made her feel, in danger. All I had to think about was helping her. The doctors visited Natasha both separately and in consultations, spoke a lot of French, German and Latin, condemned each other, prescribed a wide variety of medicines for all the diseases known to them; but not one of them had the simple thought that they could not know the disease that Natasha suffered from, just as no disease that is possessed by a living person could be known: for every living person has his own characteristics and always has a special and its own new, complex, unknown to medicine disease, not a disease of the lungs, liver, skin, heart, nerves, etc., recorded in medicine, but a disease consisting of one of the countless compounds in the suffering of these organs. This simple thought could not occur to doctors (just as the thought that he cannot cast magic cannot occur to a sorcerer) because their life’s work was to heal, because they received money for this, and because They spent the best years of their lives on this matter. But the main thing is that this thought could not occur to the doctors because they saw that they were undoubtedly useful, and were truly useful for all the Rostovs at home. They were useful not because they forced the patient to swallow mostly harmful substances (this harm was little sensitive, because harmful substances were given in small quantities), but they were useful, necessary, inevitable (the reason is why there are and will always be imaginary healers, fortune tellers, homeopaths and allopaths) because they satisfied the moral needs of the patient and the people who love the patient. They satisfied that eternal human need of hope for relief, the need for sympathy and activity that a person experiences during suffering. They satisfied that eternal, human - noticeable in a child in the most primitive form - need to rub the place that is bruised. The child is killed and immediately runs into the arms of the mother, the nanny, so that they can kiss and rub the sore spot, and it becomes easier for him when the sore spot is rubbed or kissed. The child does not believe that his strongest and wisest do not have the means to help his pain. And the hope of relief and expressions of sympathy while his mother rubs his lump comfort him. The doctors were useful to Natasha because they kissed and rubbed the bobo, assuring that it would pass now if the coachman went to the Arbat pharmacy and took seven hryvnia worth of powders and pills in a nice box for a ruble, and if these powders would certainly be in two hours, no more and no less, the patient will take it in boiled water.
What would Sonya, the count and countess do, how would they look at the weak, melting Natasha, doing nothing, if there were no these pills by the hour, a warm drink, chicken cutlet and all the details of life prescribed by the doctor, which were an occupation and a consolation for those around him to observe? The stricter and more complex these rules were, the more comforting it was for those around them. How would the count bear the illness of his beloved daughter if he did not know that Natasha’s illness cost him thousands of rubles and that he would not spare thousands more to do her good: if he did not know that if she did not recover, he would not he will spare thousands more and take her abroad and hold consultations there; if he had not had the opportunity to tell details about how Metivier and Feller did not understand, but Frieze understood, and Mudrov defined the disease even better? What would the Countess do if she could not sometimes quarrel with the sick Natasha because she did not fully comply with the doctor’s instructions?
“You’ll never get well,” she said, forgetting her grief out of frustration, “if you don’t listen to the doctor and take your medicine at the wrong time!” After all, you can’t joke about it when you could get pneumonia,” said the countess, and in the pronunciation of this word, which was incomprehensible to more than one word, she already found great consolation. What would Sonya do if she did not have the joyful knowledge that she did not undress for three nights at first in order to be ready to carry out exactly all the doctor’s orders, and that she now does not sleep at night in order not to miss the clock , in which you should give low-harm pills from a golden box? Even Natasha herself, who, although she said that no medicine would cure her and that all this was nonsense, was happy to see that they made so many donations for her that she needed famous watches take medications, and even she was happy that, by neglecting to follow the prescribed instructions, she could show that she did not believe in treatment and did not value her life.
The doctor went every day, felt her pulse, looked at her tongue and, not paying attention to her murdered face, joked with her. But when he went into another room, the countess hurriedly followed him out, and he, assuming a serious look and shaking his head thoughtfully, said that, although there was danger, he hoped that this last medicine would work, and that he had to wait and see ; that the disease is more moral, but...
The Countess, trying to hide this act from herself and from the doctor, slipped a gold piece into his hand and each time returned to the patient with a calmed heart.
The signs of Natasha's illness were that she ate little, slept little, coughed and never perked up. The doctors said that the patient could not be left without medical care, and therefore they kept her in the stuffy air in the city. And in the summer of 1812 the Rostovs did not leave for the village.
Despite the large number of swallowed pills, drops and powders from jars and boxes, from which Madame Schoss, a hunter for these things, collected a large collection, despite the absence of the usual village life, youth took its toll: Natasha’s grief began to be covered with a layer of impressions of the life she had lived, it It stopped being such an excruciating pain on her heart, it began to become a thing of the past, and Natasha began to physically recover.

Natasha was calmer, but not more cheerful. She not only avoided all external conditions of joy: balls, skating, concerts, the theater; but she never laughed so hard that tears could not be heard from her laughter. She couldn't sing. As soon as she began to laugh or tried to sing to herself alone, tears choked her: tears of repentance, tears of memories of that irrevocable, pure time; tears of frustration that she had ruined her young life, which could have been so happy, for nothing. Laughter and singing especially seemed to her a blasphemy to her grief. She never thought about coquetry; she didn't even have to abstain. She said and felt that at that time all men were for her exactly the same as the jester Nastasya Ivanovna. The inner guard firmly forbade her any joy. And she didn’t have all the old interests of life from that girlish, carefree, hopeful way of life. Most often and most painfully, she remembered the autumn months, the hunt, her uncle and the Christmastide spent with Nicholas in Otradnoye. What would she give to bring back just one day from that time! But it was over forever. The premonition did not deceive her then that that state of freedom and openness to all joys would never return again. But I had to live.
She was pleased to think that she was not better, as she had previously thought, but worse and much worse than everyone, everyone in the world. But this was not enough. She knew this and asked herself: “What next?” And then there was nothing. There was no joy in life, and life passed. Natasha, apparently, was only trying not to be a burden to anyone and not to disturb anyone, but she didn’t need anything for herself. She moved away from everyone at home, and only with her brother Petya did she feel at ease. She loved being with him more than with others; and sometimes, when she was with him face to face, she laughed. She almost never left the house and of those who came to them, she was only happy with Pierre. It was impossible to treat her more tenderly, more carefully and at the same time more seriously than Count Bezukhov treated her. Natasha Oss consciously felt this tenderness of treatment and therefore found great pleasure in his company. But she was not even grateful to him for his tenderness; nothing good on Pierre's part seemed like an effort to her. It seemed so natural to Pierre to be kind to everyone that there was no merit in his kindness. Sometimes Natasha noticed Pierre's embarrassment and awkwardness in her presence, especially when he wanted to do something pleasant for her or when he was afraid that something in the conversation would bring up difficult memories for Natasha. She noticed this and attributed it to his general kindness and shyness, which, according to her ideas, the same as with her, should have been with everyone. After those unexpected words that if he were free, he would be on his knees asking for her hand and love, spoken in a moment of such strong excitement for her, Pierre never said anything about his feelings for Natasha; and it was obvious to her that those words, which had so comforted her then, were spoken as all sorts of meaningless words are spoken to console a crying child. Not because Pierre was a married man, but because Natasha felt between herself and him to the highest degree that force of moral barriers - the absence of which she felt with Kyragin - it never occurred to her that she could get out of her relationship with Pierre not only love on her part, or, even less, on his part, but even that kind of tender, self-recognizing, poetic friendship between a man and a woman, of which she knew several examples.
At the end of Peter's Lent, Agrafena Ivanovna Belova, the Rostovs' neighbor from Otradnensky, came to Moscow to bow to the Moscow saints. She invited Natasha to fast, and Natasha happily seized on this idea. Despite the doctor’s prohibition from going out early in the morning, Natasha insisted on fasting, and fasting not as they usually fasted in the Rostovs’ house, that is, to attend three services at home, but to fast as Agrafena Ivanovna fasted, that is, for the whole week without missing a single vespers, mass or matins.

Daphnia are river crustaceans that are widely used in aquarium farming, since they are the universal food for many aquarium inhabitants. These crustaceans in natural conditions live in ponds, but breeding daphnia at home is also possible. Most often, the type of crayfish that is bred at home is the Daphnia moina species, and how to breed it at home will be discussed further.

Speaking about how to breed daphnia at home, it is worth preparing in advance not only the container, but also knowing what to feed these microscopic crustaceans and how to create the necessary conditions.

Tara

For growing at home, containers with a volume of 15-20 liters are perfect. When choosing containers, you should take into account the following recommendations:

Physical conditions for keeping daphnia

1. Salinity. Since these are freshwater crustaceans, the water in artificial reservoir for them it must be fresh.
2. Oxygen. Daphnia crustaceans are tolerant of oxygen levels in water, which can vary from zero to saturated. In this case, it is worth saying that daphnia does not tolerate too active aeration of water in an artificial reservoir, with the release of small bubbles, as well as slow aeration with the release of large bubbles, which will form foam on the surface of the water.
3. Regarding the level of ammonia in water and the pH level of water, the optimal indicators are water acidity in the range of 6.5-9.5 and optimum indicators of 7.2 - 8.5
4. Speaking about the optimal temperature regime, daphnia, photos of which can be found above or in specialized literature, can live in water with a wide temperature range. The optimal temperature for breeding is between 18-22 degrees.

What to feed

If you breed daphnia at home, beginners naturally have the question of what to feed these crustaceans. Daphnia moina in natural conditions feeds on bacteria and yeast, as well as microplanton.

Bacteria can be obtained from banana peels, food waste, and ordinary excrement, which is pre-soaked in water and infused for several days. As a rule, the water begins to become cloudy, which indicates the reproduction and growth of bacteria - the maximum effect will be achieved in 6-7 days.

Such cloudy nutrient water is added to containers of 450 ml per 20 liters, every 5-6 days.

Yeast is another nutritious food. In this case, the simplest baker's dry yeast or wet yeast sold in packs will do. They are added at the rate of 28 grams per 20 liters of water - this is the daily norm for daphnia, while at the same time adding microscopic algae, which will prevent water pollution and serve as an additional nutritional component for small crustaceans.

The advantage of yeast as a nutritional component is that it is easy to use and purchase, but it is less valuable than algae. Microscopic algae must be supplied to daphnia in large quantities - you yourself could see that in places where algae bloom in lakes and ponds, daphnia predominate in large quantities.

The advantage of using algae in food is their ease of use - it is optimal to choose algae of the Scendesmus family, as well as chlorella, which develop in large quantities in a newly equipped, stocked aquarium. It is enough to scoop up water from such an aquarium and place it in a warm place under the sun’s rays - the algae will actively develop, serving in the future as food for daphnia.

You can add beet juice or cabbage or carrot juice to the water containing daphnia - 1 tsp. per 5 liters of volume - this will not only diversify the diet of crustaceans, but also serve as a source of vitamins for them. Adding liquid manure in small doses also has an excellent effect, but experienced aquarists do not recommend adding milk or hay infusion - they stop the growth and reproduction of daphnia.

Aeration

When talking about how to breed daphnia, novice aquarists may ask: is aeration necessary when growing and cultivating crayfish? Experienced experts say that it is desirable, especially when growing Daphnia moina. It enriches the water with oxygen, promotes the development of phytoplankton and prevents the formation of a film on the surface of the water. The main thing is that aeration should be of medium intensity, since a strong air flow will disturb them, and a flow with small bubbles will accumulate under the shell of the crayfish and lift them to the surface.

How to increase productivity during development?

This process is simple and even a beginner, puzzled by the question of how to breed crustaceans, can handle it. In this case, take into account a number of specific recommendations:

1. Good aeration, with uniform air flow and the absence of too small or large bubbles. This is precisely the first condition for increasing productivity in the process of reproduction of river crustaceans. In this regard, experienced aquarists recommend using an airlift filter in containers with daphnia, which is used in cages with fry.
2. Maintaining the cleanliness of the habitat and regularly changing the composition of the water - if the volume of the aquarium containing crayfish is large, it is recommended to replace ¾ of the composition of the water.
3. Regular collection of culture will help maintain constant reproduction and growth of daphnia at the proper level.
4. A 24-hour daylight period can also increase growth and active reproduction many times over. Of course, this is not a prerequisite, but it significantly increases the growth and reproduction of this microscopic river crustacean. At the same time, the minimum duration of daylight hours for them should be at least 18 hours.


5. The regime and percentage of water replacement in the container containing daphnia - in this aspect it is worth considering what kind of food is used, how much of the artificial reservoir is and the number of daphnia in it. But in any case, this is necessary to purify water from metabolic products of microorganisms and toxins.

As you can see, it is quite easy to breed daphnia, which not only serves as a nutritious and versatile food for your own fry and fish, but is also a great idea for a home business.

aquariumax.ru

Taxonomy[edit | edit code]

One of the largest (more than 50 valid species in the world fauna) and difficult for taxonomy of the cladoceran genera. Typical view - D. longispina O.F. Mueller, 1785. The most characteristic distinguishing feature of the genus is the antennae of females fused to the head. In addition, females usually have a well-developed rostrum, and the ventral margin of the valves is convex. In both sexes, the valves, as a rule, bear spines and form an unpaired outgrowth - a tail spine. In most species (except some Australian species, often classified as Daphniopsis) There are two eggs in the ephippium. All setae of antenna II are ordinary, with long setulae.

Most taxonomists recognize the division of this genus into two subgenera - Daphnia (Daphnia) O.F. Mueller, 1785 and Daphnia (Ctenodaphnia) Dybowski et Grochjwski, 1895. In the subgenus Daphnia (Daphnia) there is no notch for the head shield; the egg chambers of the ephippium are usually almost perpendicular to the dorsal margin of the valves. In representatives of the subgenus Daphnia (Ctenodaphnia) there is a notch in the head shield; the egg chambers of the ephippium are usually almost parallel to the dorsal margin of the valves. All species previously assigned to the genus Daphniopsis, are part of the subgenus Daphnia (Ctenodaphnia), and many of them have primitive (no notch of the head shield) or evasive (one egg in the ephippium) characters.

Types of Daphnia[edit | edit code]

• Daphnia ambigua Scourfield, 1947
• Daphnia atkinsoni Baird, 1859
• Daphnia arcuata Forbes, 1893
• Daphnia australis(Sergeev et Williams, 1985)
• Daphnia barbata Weltner, 1898
• Daphnia bolivari Richard, 1888
• Daphnia brooksi Dodson, 1985
• Daphnia carinata King, 1852
• Daphnia carvicervix Ekman, 1901
• Daphnia catawba Coker, 1926


• Daphnia cheraphila Hebert and Finston, 1996
• Daphnia chevreuxi Richard, 1896
• Daphnia cristata G. O. Sars, 1862 - Daphnia crested
• Daphnia cucullata G. O. Sars, 1862)
• Daphnia curvirostris Eylmann, 1887
• Daphnia dadayana Daday, 1902
  sensu Paggi, 1999
• Daphnia dubia Herrick, 1883
• Daphnia dolichocephala G.O. Sars, 1895
• Daphnia ephemeralis(Schwartz et Hebert, 1985)
• Daphnia exilis Herrick, 1895
• Daphnia galeata G. O. Sars, 1864
• Daphnia gessneri Herbst, 1968
• Daphnia hispanica Glagolev et Alonso, 1990
• Daphnia hyalina Leydig, 1860
• Daphnia jollyi Petkovski, 1973
• Daphnia lacustris G.O. Sars, 1862
• Daphnia laevis Birge, 1879
• Daphnia latispina Korinek and Hebert, 1996
• Daphnia longiremis G. O. Sars, 1862
• Daphnia longispina O. F. Mueller, 1785)
• Daphnia lumholtzi G. O. Sars, 1885
• Daphnia magna Straus, 1820
• Daphnia magniceps Herrick, 1884
• Daphnia mediterranea Alonso, 1985
• Daphnia menucoensis Paggi, 1996
• Daphnia middendorffiana Fischer, 1851
• Daphnia minnehaha Herrick, 1884
• Daphnia nivalis Hebert, 1977
• Daphnia occidentalis Benzie, 1986


• Daphnia obtusa Kurz, 1875
• Daphnia oregonensis Korinek and Hebert, 1996
• Daphnia pamirensis Rylov, 1928
• Daphnia parvula Fordyce, 1901
• Daphnia peruviana Harding, 1955
• Daphnia pileata Hebert and Finston, 1996
• Daphnia prolata Hebert and Finston, 1996
• Daphnia psittacea Baird, 1850
• Daphnia pulex Leydig, 1860)
• Daphnia pulicaria Forbes, 1893
• Daphnia pusilla(Serventy, 1929)
• Daphnia retrocurva Forbes, 1882
• Daphnia quadrangula(Sergeev, 1990)
• Daphnia queenslandensis(Sergeev, 1990)
• Daphnia rosea G. O. Sars, 1862
• Daphnia salina Hebert and Finston, 1993
• Daphnia schoedleri G. O. Sars, 1862
• Daphnia similis Claus, 1876
• Daphnia similoides Hudec, 1991
• Daphnia sinevi Kotov, Ishida et Taylor, 2006
• Daphnia stuederi(Ruhe, 1914)
• Daphnia tanakai Ishida, Kotov et Taylor, 2006
• Daphnia tenebrosa G. O. Sars, 1898
• Daphnia tibetana(G.O. Sars, 1903)
• Daphnia thomsoni G.O. Sars, 1894
• Daphnia thorata Forbes, 1893
• Daphnia triquetra G.O. Sars, 1903
• Daphnia truncata Hebert and Wilson, 2000
• Daphnia turbinata G.O.Sars, 1903
• Daphnia umbra
• Daphnia villosa Korinek and Hebert, 1996
• Daphnia wardi Hebert and Wilson, 2000

External structure[edit | edit code]

Unless otherwise stated, this section describes the anatomy of females. The integument consists of a head shield and a bivalve carapace. Usually they have a clearly visible pattern of rhombuses and polygons - reticulation. Each such cell of the integument is formed by one cell of the hypodermis. There are spines at the edge of the valves, and at the posterior end there is a tail spine covered with spines. Many species have a row of feathered setae on the inner edge of the valves in its middle part; males of all species have the same setae and additional setae on the anterior-inferior corner of the valves.

On the head of most species, a beak-like outgrowth is developed - the rostrum. Below it are located the first antennae (antennales) - short projections bearing at the end 9 olfactory setae - aesthetascus (aesthetascus), and on the lateral surface - one additional seta. In males, the first antennae are larger, more mobile, and, in addition to aesthetascae, bear a large seta (“flagellum”) at the distal end.

On the lateral surface of the head there are projections of the cuticle - fornixes. Their shape, as well as the shape of the posterior edge of the head shield, is an important diagnostic feature of subgenera and groups of species. Under the fornix, second antennae (antennae) are attached to the head by a complex “joint”. They consist of a base and two branches - an internal three-segmented and an external four-segmented. At the ends of the segments of the branches there are two-segmented swimming setae covered with flattened hairs, forming “oars” when swimming. There are five of them on the three-segmented branch (four only in D. cristata), on a four-segmented one - four. There are several small sensitive bristles on the base.

A large upper lip extends from the back of the head. Inside it there are several giant polyploid cells that secrete a secretion that glues the food into a food bolus.

On the border between the head shield and the carapace, mandibles are located under the valves. They have a complex shape, are asymmetrical and have highly chitinized chewing surfaces covered with ridges and outgrowths. During feeding, the mandibles transport food into the mouth opening.

Under the carapace there are small maxillae 1 (maxillulae), bearing four setae. The second maxillae in Daphnia are reduced. There are five pairs of two-branched thoracic legs of complex structure. The legs of the first and partly the second pair differ in structure in males and females. On the first pair of legs of males there are hook-shaped projections that allow them to cling to females during mating. The third and fourth pairs carry fans of filter bristles. Each leg has a respiratory appendage - an epipodite.

Behind the thoracic region there is a reduced abdominal region, the presence of which is “marked” by dorsal abdominal processes that cover the exit from the brood chamber. There are usually four of them, they are well developed in mature females and reduced in males of most species.

The posterior part of the body is a large mobile post-abdomen, homologous to the telson of other crustaceans. On its dorsal side there are two rows of denticles, between which is the anus. In males of some species these denticles are partially or completely reduced. At the end of the postabdomen there are paired claws covered with spines. According to some data, they are homologous to the furca, according to others, they are a pair of large modified setae. There are spines on the outer and inner sides of the claws; usually there are three groups of spines on the outer side and two on the inner side. The post-domain serves to clean the filtration apparatus from large foreign particles.

Internal structure[edit | edit code]

The integumentary system of daphnia is represented by a typical hypodermis. The hypodermis of the carpax consists of large cells forming rhombic-shaped cells.

The central nervous system consists of the suprapharyngeal ganglion (brain) and the ventral nerve cord with several paired ganglia. The brain is clearly visible in living individuals, which is extremely rare. It consists of a large, bisected optic ganglion and the suprapharyngeal ganglion proper. The optic nerve arises from the anterior part of the optic ganglion and connects the brain to the compound eye. The unpaired compound eye in Daphnia is formed from a paired rudiment (embryos have two eyes) and contains exactly 22 facets (ommatidium). It is located in a special cavity inside the head, to the walls of which it is suspended by two ligaments (ligaments) and driven by three pairs of extraocular muscles. In living individuals, tremor of the eye is noticeable, and from time to time larger jumps (saccades) of the eye are observed. Nerves also extend from the brain to the ocellus (simple eye), the first antennae (at their base there is a sensitive ganglion, the cells of which innervate the olfactory bristles - aesthetes), as well as nerves to the sensitive occipital organ of unknown purpose. Adjacent to the lower part of the suprapharyngeal ganglion is the simple eye (ocelli, nauplial eye). In most species it contains pigment and is visible as a small black dot. There are 4 groups of sensitive cells around the pigment spot.

Daphnia has a complex system of striated muscles that move the second antennae, post-abdomen and thoracic limbs, as well as muscles that move the eyes, upper lip, etc. The muscles of the digestive tract are also striated.

The digestive tract begins with the oral opening, which is covered by a large upper lip. Giant highly polyploid cells located inside the lip secrete a secretion that glues food into a food bolus. Through the movements of the mandibles, it is transported into the thin esophagus, the dilator muscles of which create peristalsis, ensuring the transport of food through the esophagus. Inside the head, the esophagus passes into the wider midgut, which extends to the middle part of the post-abdomen. Inside the head, two curved liver processes extend from the midgut. In the posterior part of the post-abdomen there is a short hindgut.

The heart is located on the dorsal side of the body, in front of the edge of the brood chamber. Blood (hemolymph), the flow of which is clearly visible due to the presence of colorless cells in it - phagocytes, enters the heart through the ostia - two slit-like side openings. When the heart contracts, the ostia close with valves, and blood is ejected through the anterior opening to the head. There are no blood vessels; the regular direction of blood flow is ensured by transparent partitions between different parts of the myxocoel.

Breathing occurs through the integument of the body, primarily the thoracic legs, on which there are respiratory appendages - epipodites. The latter also take part in osmoregulation. An additional organ of osmoregulation in newborns is the large nuchal pore (occipital organ), which disappears after the first postembryonic molt.

The excretory organs are complex-shaped maxillary glands, which are located on the inner surface of the valves in their anterior part.

Paired ovaries (testes in males) are located on the sides of the intestines. At the posterior end there is a breeding zone for oogonia; the rest of the ovary is filled with maturing oocytes. As the eggs mature, they move to their posterior third, where there are narrow oviducts that open into the brood chamber. In males, the vas deferens open on the postabdomen in its distal part, and in many species on special papillae.

Shedding[edit | edit code]

During molting, the cervical suture, the line between the head shield and the carapace, separates, and the animal emerges from the exuvium. Together with the carapace, the integument of the body and limbs is shed. Molting occurs periodically throughout the life of the individual. Typically, molting occurs in the water column; ephippial females of some species molt, sticking from below to the surface film of the water. Several molts occur during embryonic development, in the brood chamber.

Distribution[edit | edit code]

Genus Daphnia has a worldwide distribution (including Antarctica, where in the relict salt lakes of the Vestfold oasis ( Westfold Hills) was found Daphnia studeri, previously classified as a genus Daphniopsis). At the beginning of the 20th century, the prevailing opinion was that most species had a cosmopolitan distribution, but it later became clear that the faunas of different continents differ greatly. Some species, however, have very wide ranges and are distributed on several continents. The smallest number of species is typical for equatorial regions, where daphnia are rare. The most diverse fauna is in the subtropics and temperate latitudes. In recent decades, the ranges of many species have changed due to human dispersal. Thus, a species from the New World was introduced into Europe (England) D.ambigua. It has become common in many reservoirs in the southern United States. D. lumholtzi, which was previously found only in the Old World.

In ponds and puddles in central Russia, the following crustaceans of the genus Daphnia are often found (and most popular among aquarists):

Daphnia magna (D. magna), female - up to 6 mm, male - up to 2 mm, newborns - 0.7 mm. They ripen within 10-14 days. Litters in 12-14 days. There are up to 80 eggs in a clutch (usually 20-30). Life expectancy is up to 3 months.

Daphnia pulex (D. pulex), female - up to 3-4 mm, male - 1-2 mm. Litters in 3-5 days. There are up to 25 eggs in a clutch (usually 10-12). They live 26-47 days.

In lakes of the temperate zone of Eurasia they are often found D. cucullata, D. galeata, D. cristata and several other types.

Biology[edit | edit code]

Daphnia are small crustaceans (the body size of adults is from 0.6 to 6 mm). They inhabit all types of standing continental bodies of water and are also found in many slow-flowing rivers. In puddles, ponds and lakes they often have high numbers and biomass. Daphnia are typical planktonic crustaceans, spending most of their time in the water column. Various species inhabit shallow temporary reservoirs. littoral and pelagic zones of lakes. Quite a few species, especially those inhabiting arid areas, are halophiles, living in brackish, saline and hypersaline continental water bodies. These types include, for example, D. magna, D. atkinsoni, D.mediterranea, as well as most species previously classified in the genus Daphniopsis.

Locomotion[edit | edit code]

They spend most of their time in the water column, moving in sharp leaps due to the flapping of the second antennae, which are covered with special feathered bristles (hence their common name - “water fleas,” often applied to all cladocerans). Many daphnia are also capable of slowly crawling along the bottom or walls of vessels due to water currents created by the thoracic legs (the antennae are motionless with this method of movement).

Food[edit | edit code]

The main food for daphnia are bacteria and unicellular algae. Species that survive the winter in an active state (in deep, non-freezing reservoirs) spend it in the bottom layers of water, feeding mainly on detritus. They feed by filtration, creating currents of water with rhythmic movements of the chest legs. Food is filtered by fans of filtering setae, which are located on the endopodites of the III and IV pairs of thoracic legs. Large particles stuck in the filtration apparatus (for example, filamentous algae) are removed using the postabdomen and its claws. From the filtering fans, food enters the abdominal food groove, is transmitted to the maxillae of the first pair and then to the mandibles, the movements of which transport it to the esophagus. In front, the mouth opening of daphnia is covered with a large upper lip, inside which there are salivary glands from giant polyploid cells. Their secretion glues food particles together into a food bolus.

At an average concentration of food in water, adult daphnia of various species are filtered at a rate of 1 to 10 ml/day. Daily food intake for adults D. magna can reach 600% of her body weight.

Gas exchange[edit | edit code]

On the thoracic legs there are sac-like respiratory appendages - gills. Probably, a significant part of the oxygen of daphnia is obtained through the thin integument of the body and limbs, and the respiratory appendages, like the occipital organ of newborns, play an important role in osmoregulation. Some types (for example, D. pulex, D. magna) with a low oxygen content in the water, they begin to synthesize hemoglobin, so that their hemolymph and the whole body turns red.

Cyclomorphosis[edit | edit code]

Many species of daphnia (mainly living in lakes) exhibit cyclomorphosis - their different generations, developing in different seasons of the year, differ sharply in body shape. In temperate latitudes, summer generations of such species have elongated cuticle outgrowths - a tail spine and a head shield. In spring and autumn generations, the tail spine is shorter, the helmet may be shorter or absent altogether. It has been shown that growing outgrowths requires energy expenditure and leads to a decrease in fertility. Among the factors causing the growth of outgrowths of the integument, the influence of increased water turbulence, high temperature, etc. was demonstrated. Later it was shown that the main influence on the growth of cyclomorphic outgrowths is exerted by kairomones - signaling substances secreted by different types of invertebrate and vertebrate predators. Many hypotheses have been put forward about the adaptive role of cyclomorphosis: easier soaring in less dense and viscous water, accelerated swimming in the horizontal direction, etc. Most of them are either unproven or refuted. Nowadays, the theory about the role of outgrowths in protection from predators is accepted as the main explanation for cyclomorphosis. Transparent outgrowths increase the actual size of the body and thereby protect against small invertebrate predators - larger prey with outgrowths are more difficult to grab and not release during manipulation - “stuffing into the mouth.” Sometimes the tail spine breaks off, which can play the same role as autotomy of the tail in a lizard. At the same time, transparent outgrowths do not increase the apparent size, which is important for protection from large visual predators - fish.

Vertical migrations[edit | edit code]

Like other representatives of zooplankton, daphnia make vertical migrations in many bodies of water - both large and deep, and shallow. Almost always, these migrations are diurnal in nature: in the daytime, crustaceans move to deeper bottom layers, and in the dark, they rise to the surface. Among the many theories that explain the causes of migrations, on which a significant percentage of energy is spent, the theory that connects migrations with the same protection from predators is now considered the most substantiated. During daylight hours, larger species, clearly visible to visual predators, are forced to descend into deep, poorly lit layers of water to protect themselves from being eaten by fish. Migrations in the same Daphnia species can be well expressed in lakes where there are many fish, and absent in lakes where planktivorous fish are absent.

Reproduction and dispersal[edit | edit code]

Most daphnia (like other cladocerans) are characterized by cyclic parthenogenesis. In favorable conditions (for example, in summer in non-drying puddles and shallow reservoirs), only parthenogenetic females are present in daphnia populations. From their unfertilized diploid eggs, the next generations of females develop. Since parthenogenesis in daphnia is ameiotic, their reproduction is clonal (populations consist of clones - the offspring of individual females). The development of embryos during parthenogenesis occurs in the brood chamber under the shell and is accompanied by several molts. Then the young crustaceans emerge from the brood chamber (direct development).

In the fall or before the reservoir dries up, males develop from the same unfertilized eggs (as a rule, all individuals of the same litter have the same sex). Thus, sex determination in Daphnia is purely environmental.

The transition to bisexual reproduction in species from large bodies of water usually requires exposure to two stimuli - a decrease in temperature and a decrease in the length of daylight hours. It is hypothesized that these and other stimuli act by reducing the female's food intake. Male daphnia are smaller in size and differ significantly from females in the structure of the first antennae and thoracic legs. They swim faster than females and mate with them, attaching themselves to the rear edge of the shell. Fertilization in Daphnia is internal.

In recent years, it has been shown that the development of males can be induced by adding to the medium the juvenile hormone of crustaceans methyl farnesoate, as well as analogues of the juvenile hormone of insects - the insecticide fenoxycarb.

During the period of bisexual reproduction, some females give birth to males, while others at the same time form resting, or ephippial, eggs. They are formed by meiosis and require fertilization to develop. After fertilization, they also exit into the brood chamber, the covers of which thicken and form a special chitinous chamber - the ephippium (ephippium). Most Daphnia species have two eggs in the ephippium; in some Australian species, often classified as a separate genus Daphniopsis, there is one egg in the ephippium. In species of the subgenus Daphnia the long axes of the eggs are perpendicular to the dorsal margin of the ephippium, in species of the subgenus Ctenodaphnia- parallel to it or inclined at a slight angle. Egg development continues until the gastrula stage, then they enter suspended animation. During the next molt, the female sheds the ephippium, which in some species usually sinks to the bottom, while in others it floats on the surface of the reservoir. When laying effipium, females of some species (for example, D. pulex) often die. Together with ephippiums, daphnia eggs are carried by the wind, spreading on the paws of mammals, on the paws and feathers of birds, as well as in their intestines. It has also been shown that floating ephippiums can stick to the body of smooth bugs taking off from the surface of the water and be carried by them, and more often smooth ephippiums are carried by smaller ephippiums. Eggs in a chemically resistant shell inside the ephippium can remain viable after passing through the intestines of birds and fish. They usually also withstand freezing and prolonged drying. It has been shown that resting daphnia eggs can survive and develop for a long time in solutions of toxic salts (for example, mercuric chloride HgCl 2) at a concentration of poisons thousands of times higher than the maximum permissible concentration; after the egg shell ruptures, the hatched embryos in such solutions immediately die.

Use in scientific research[edit | edit code]

Daphnia are used as model organisms in many environmental, toxicological and genetic studies.

Decoding the genome[edit | edit code]

In recent years, the Daphnia genome has been partially deciphered Daphnia pulex, its draft was completed in 2011. The Daphnia genome consists of 200 million nucleotides, but it contains at least 30.9 thousand genes - more than other multicellular animals that have been studied so far (for example, the human genome has about 20-25 thousand genes). The Daphnia genome was characterized by a high rate of gene duplications, which led to the creation of numerous gene clusters. More than a third of the gene products found in the Daphnia genome have no known homologs in the proteomes of other organisms. The largest amplified gene families are also characteristic only of this evolutionary line. Many paralog genes are expressed differently depending on environmental conditions; genes unique to daphnia are most sensitive to changes in conditions. It can be assumed that gene duplications increased the ecological plasticity of daphnia, allowing them to adapt to the conditions of different reservoirs and to changing conditions in the same reservoir.

Breeding[edit | edit code]

Cultivation of daphnia as food is widespread, both for industrial purposes and by amateur aquarists. In favorable conditions, daphnia reproduce and grow easily and quickly, which makes it possible to obtain 30-50 (in some cases up to 100) grams of crustaceans per day from one cubic meter of culture.

The source culture can easily be obtained from natural reservoirs. It is advisable to catch crustaceans in small bodies of water, where the daphnia population can be practically free from the admixture of other animals. In winter, a culture of daphnia can be obtained from ephippial resting eggs, previously collected from the surface of the water or from the upper layer of silt. Collected ephippiums are well preserved in a dry state in a cool room.

Depending on the required number of crustaceans, daphnia can be cultivated both in small vessels and in large pools and ponds. The optimal density of the crop is 300-1000 g/m³. Periodically, every few weeks or months, the culture is replanted. The aging of a crop is associated with the accumulation of metabolic and decomposition products in it and with its contamination by other organisms. When changing water, the life of the crop is extended.

The optimal growing temperature is 15-25°C, the medium reaction is neutral (pH 6.8-7.8), oxygen content is at least 3-6 mg/l, oxidability is 14.8-26.2 mg O 2 /l.

When growing daphnia, both joint and separate cultivation of crustaceans and food for them are used.

When grown together, organic fertilizers are added to the crop, for example, manure applied in an amount of 1.5 kg/m3. It is possible to grow on mineral fertilizers, the addition of which causes the rapid development of unicellular algae.

The disadvantages of co-cultivation are severe water pollution, rapid aging of the culture and rapid overgrowing of the container with filamentous algae.

Separate cultivation of daphnia and food for them does not have these disadvantages, but is technically more complex and is used mainly in conditions of mass industrial cultivation of feed crustaceans. In this case, an algal culture is grown separately, which is added to the container with daphnia 1-2 times a day.

In laboratory and home conditions, it is convenient to maintain a culture of daphnia with yeast, added daily little by little in the amount of 15-20 g per cubic meter of culture (15-20 mg/l). . Standardized methods for laboratory culture of Daphnia are described in toxicology and bioassay manuals.

Other facts[edit | edit code]

Live, dried and frozen daphnia are often used as food for aquarium fish or insects kept in terrariums. In industrial fish farming, breeding daphnia for food is of great importance.

Daphnia is one of the standard objects for testing the toxicity of aqueous solutions of chemical compounds used in the study of aquatic environmental pollution. Daphnia are sensitive even to small concentrations of some salts, for example, the addition of copper salts at a concentration of 0.01 mg/l causes the movements of the crustaceans to slow down, they either sink to the bottom or freeze at the surface film of water.

Literature[edit | edit code]

• Peters P.H., De Bernardi R. Daphnia // Mem. Ist. Ital. Idrobiol. - 1987. - V. 45. - 502 p.
• John K. Colbourne, Michael E. Pfrender, Donald Gilbert, W. Kelley Thomas, Abraham Tucker, Todd H. Oakley, Shinichi Tokishita, Andrea Aerts, Georg J. Arnold, Malay Kumar Basu, Darren J. Bauer, Carla E. Cáceres , Liran Carme, Claudio Casola, Jeong-Hyeon Choi, John C. Detter, Qunfeng Dong, Serge Dusheyko, Brian D. Eads, Thomas Fröhlich, Kerry A. Geiler-Samerotte, Daniel Gerlach, Phil Hatcher, Sanjuro Jogdeo, Jeroen Krijgsveld1, Evgenia V. Kriventseva, Dietmar Kültz, Christian Laforsch, Erika Lindquist, Jacqueline Lopez, J. Robert Manak, Jean Muller, Jasmyn Pangilinan, Rupali P. Patwardhan, Samuel Pitluck, Ellen J. Pritham, Andreas Rechtsteiner, Mina Rho, Igor B. Rogozin, Onur Sakarya, Asaf Salamov, Sarah Schaack, Harris Shapiro, Yasuhiro Shiga, Courtney Skalitzky, Zachary Smith, Alexander Souvorov, Way Sung, Zuojian Tang, Dai Tsuchiya, Hank Tu, Harmjan Vos, Mei Wang, Yuri I. Wolf, Hideo Yamagata, Takuji Yamada1, Yuzhen Ye, Joseph R. Shaw, Justen Andrews, Teresa J. Crease, Haixu Tang, Susan M. Lucas, Hugh M. Robertson, Peer Bork, Eugene V. Koonin, Evgeny M. Zdobnov, Igor V. Grigoriev, Michael Lynch, Jeffrey L. Boore. The Ecoresponsive Genome of Daphnia pulex// Science. - 2011. - Vol. 331, No. 6017. - P. 555-561. - DOI:10.1126/science.1197761.
• Ivleva I. V. Biological principles and methods of mass cultivation of food invertebrates. - M.: Nauka, 1969. - 171 p.
• Makrushin A.V., Lyanguzova I.V. The shell of propagules of invertebrates and plants: selective permeability and barrier properties // Journal of General Biology. - 2006. - T. 67, No. 2. - P. 120-126.
• Shpet G.I. Breeding daphnia as live food in fish farming // Proceedings of the Ukrainian Institute of Pond. and lake-river fish households - 1950. - T. 7.
• Guidelines for determining the toxicity of water, bottom sediments, pollutants and drilling fluids using biotesting. - M.: REFIA, NIA-Priroda, 2002.

en.wikipedia.org

Features and habitat of daphnia

Depending on the kind daphnia, their size can range from 0.2 mm to 6 mm, so study structure of daphnia only possible under a microscope. The body of these crustaceans has an oval shape, it is covered with a special shield of two valves (carapace), which protects the internal organs.

The head is also covered with a chitinous shell and has a beak-like outgrowth (rastrum), under which are located the anterior antennae, which perform an olfactory function.

The size of the rear antennas is much more impressive compared to the front ones; their main task is the movement of daphnia. By flapping both antennae at the same time, daphnia pushes off from the water and swims, making sharp leaps. For this feature common daphnia often called "water flea".

On the head of the crustacean there is a compound eye, an unpaired organ responsible for vision. The number of facets depends on the species and ranges from 22 to 300. In predatory representatives, the structure of the eye is more complex and there are more facets. The nauplial ocellus is located just below the facet ocellus.

Daphnia thoracic legs, covered with many bristles, serve as a kind of filter through which the crustacean passes unicellular algae and bacteria suspended in the water. The legs make up to 500 strokes per minute.

Photo of daphnia taken at high magnification, make it possible to clearly see and internal structure crustacean. Thanks to the translucent shell, the heart, intestines, and, in females, a brood pouch with several embryos are clearly visible.

Daphnia of one kind or another can be found in almost any standing body of water - from a small pond to a deep lake. There are certain representatives of this genus of crustaceans in Eurasia, South and North America and even in Antarctica.

An important factor in their normal existence is standing water, in which there is a minimal amount of soil particles. Once in running water, daphnia filter out the soil along with algae and gradually clog their intestines.

The eaten grains of sand accumulate and do not allow the crustacean to move normally, and soon it dies. Daphnia extremely sensitive to contamination environment, therefore it is often used when checking water quality in reservoirs.

Character and lifestyle of daphnia

Daphnia prefer to spend most of their lives in the water column, where they continuously filter water saturated with single-celled microorganisms. Some species stay near the bottom, feeding on the remains of invertebrate animals and dead parts of plants. In the same way, daphnia survives the winter cold if it does not hibernate.

Nutrition

Blue-green algae, yeast and bacteria are the main food of daphnia. The highest concentration of unicellular algae is observed in “blooming reservoirs”; there, in the absence of a large number of fish, daphnia lives well and reproduces especially intensively.

Reproduction and lifespan

Interesting reproduction Daphnia - to the class Crustaceans are characterized by such a feature as parthenogenesis. This is the ability to reproduce offspring without direct fertilization.

When the living conditions of a given genus of crustaceans are sufficiently favorable, female daphnia reproduce through parthenogenesis, giving birth only to females.

On average, one individual gives birth to 10 nauplii, which in turn become capable of reproduction already on the 4th day after birth. During her life, a female daphnia produces offspring up to 25 times.

As environmental conditions worsen, males are born, and the next generation of crustaceans will reproduce eggs that need to be fertilized. Daphnia eggs, formed during such a period, grow into small embryos, they are covered with a special protective shell and go into hibernation.

In this form, daphnia embryos are able to survive both drought and severe frost. When environmental conditions return to normal, they develop into adults. The next generation will again produce only females that are capable of parthenogenesis.

Another interesting feature of Daphnia is cyclomorphosis. In different seasons of the year, individuals with different body shapes are born in the same population.

Thus, summer generations of daphnia have an elongated tail needle and a growth on the helmet. Among the many hypotheses about the feasibility of such changes, the main one is considered to be protection from predators, which are more active in the summer.

The lifespan of daphnia is short and, depending on the species, ranges from 3 weeks to 5 months. Large species such as Daphnia Magna live longer than their smaller counterparts.

The lifespan of daphnia also depends on the water temperature - the higher it is, the faster metabolic processes occur, the body develops faster, ages faster and dies.

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Description of the species

Water fleas have very interesting features buildings. Their entire body is covered in a leathery, bivalve shell, which ends in two hooks of a specific horny type. One spherical eye is characterized by significant mobility and consists of a large number of small eyes. In numerous photographs taken while observing these living creatures through a microscope, you can see all the features of such an eye.

The water flea is a type of typical planktonic crustacean that spends a significant part of its life in the water column. Ponds and puddles located in central Russia are home to the most common species of these crustaceans.

• Daphnia magna. In the photo, the female, with a body length of no more than six millimeters, and the male, with a length of only two millimeters, are clearly distinguishable. Individuals in the neonatal period are microscopic in size. The ripening period lasts two weeks. A standard clutch consists of three dozen eggs, which are laid by females every two weeks. The average lifespan of individuals does not exceed three months.
• Daphnia pulex. Females of this species have a body with a length of no more than four millimeters. The body of males is half the size. This species is incredibly prolific, with a clutch occurring every five days and consisting of fifteen eggs. The average lifespan can last one and a half months.

In addition, in the photo you can see water fleas of the species cucullata, galeata and cristata, which are frequent guests of lakes in the temperate Eurasian climate.

Habitat

The genus of water fleas has a worldwide distribution. Despite the differences in the fauna of all continents, daphnia are found almost everywhere, and their special distribution applies to several continents at once.

These crustaceans are found least in equatorial regions. The areas most populated by daphnia include the subtropics and temperate latitudes. Currently, there is a significant expansion of the habitat of water fleas, which is due to human activity.

Nutritional Features

Crustaceans are very voracious. The main food of daphnia is bacteria and unicellular algae. For species that survive the winter period in a state of wakefulness, the feeding place is the bottom layers and deep, non-freezing reservoirs. In such conditions, the main food for water fleas is detritus.

The feeding method is filtration. Of no small importance is the ability to create water currents through rhythmic movements performed by the thoracic legs. To filter food, special fans are used, located on filter-type bristles. Such an organ is located on the endopodites of the third and fourth pairs of thoracic limbs.

When large particles get stuck in the filtration apparatus, a special organ, represented by the post-abdomen and its claws, is triggered. Filtering fans serve as a transmission link for food to the ventral food groove, from which it moves to the maxillae and mandibles. The final site for the absorption of food elements is the esophagus.

Daphnia under a microscope (video)

In the photo you can see a rather large upper lip, which covers the mouth opening of water fleas. Daphnias do not have any organs that can be used to inflict bites. The lip is equipped with salivary glands, which contain giant polyploid cells. Salivary secretion glues food particles into a single lump. During the day, an adult consumes almost six hundred percent of its own weight.

You may also be interested in ​the article on moose fleas.

Harm to humans

The lower type of bivalve crustaceans, which include water fleas, do not bite. Any bites that are attributed to daphnia have nothing to do with them. However, Daphnia is indeed capable of causing some harm to humans, which is associated with the high degree of allergenicity of these crustaceans.

Amateur aquarists quite often use dry food made from daphnia, which is a powerful allergen for a quarter of the world's population. This high degree of allergenicity is associated with the dust-like suspension, which is formed as a result of the drying of crustaceans.

The harm from daphnia is not bites, but allergies, which are most often manifested by the following symptoms:

• lacrimation;
• conjunctivitis;
• dryness;
• congestion of the sinuses with symptoms of difficulty breathing;
• runny nose;
• involuntary sneezing.

At the next stage, hives and eczema may appear, which are mistaken for bites. In addition, significant skin lumps, which are also one of the symptoms of allergies and can cause severe itching, are a bit like flea bites.

Diagnosis of water flea allergy is based on a skin test. Photos of allergic urticaria and eczema are quite reminiscent of flea bites, and a person far from medicine should definitely consult with specialists who will clarify the diagnosis and develop an effective treatment plan.

Despite the fact that there are no water flea bites as such, treatment of allergic manifestations cannot be started. The first manifestations of allergies can be eliminated by using the following medications:

• antihistamines;
• inhalation type of modern corticosteroids;
• antileukotriene-type drugs.

If the allergy reaches a severe and advanced stage, the doctor may prescribe bronchodilators, hormonal glucocorticoids, and systemic steroid hormones.

How water fleas reproduce (video)

Daphnia bites are nothing more than a fantasy of most ordinary people. Small crustaceans are certainly capable of causing some harm, but in most cases it is enough to eliminate the cause of the allergy and promptly relieve the primary manifestations of this unpleasant disease.

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Fish food

For many decades, pet fish lovers have been using daphnia as food for their aquarium pets. Even in Soviet times, these small crustaceans were caught by aquarists in natural reservoirs. It is clear that they had to know exactly where daphnia lives. Then the caught crustaceans were used not only live, but also frozen and dried. Of course, it is quite difficult to keep a large number of them at home, which is why many try to freeze daphnia during the period of its mass reproduction in nature. If we talk about the nutritional value of frozen food, it is practically in no way inferior to live crustaceans. Nowadays you can easily purchase frozen daphnia in pet stores, so such independent preparation is becoming a relic of the past.

Daphnia structure

I would like to talk a little about how these cladoceran crustaceans, which we call daphnia, work. Their body is quite strongly compressed from the sides, the latter are covered with a two-leaf chitinous shell.

Usually daphnia have two eyes, which are located on the head, but sometimes mature individuals are distinguished by the presence of one compound eye, next to which there may be an additional small eye. There are also two pairs of antennas on the small head. The rear (second) pair is equipped with additional bristles and is large in size. It is thanks to the stroke of these antennae that daphnia make a kind of leap when moving. Therefore, people also call them “water fleas.”

Reproduction of crustaceans

If you look at the process of reproduction of these tiny crustaceans from a human point of view, it is very unusual. Females of this species have a so-called brood chamber, which is reliably protected by the edge of the shell and located on the back. When favorable conditions are created around, the female lays 50-100 unfertilized eggs in this cavity, where they develop. It is curious that only females hatch from these eggs and safely leave the chamber. After just a few days, the process repeats again, and young, grown and mature females will join this rapid reproduction process. That is why in summer, where daphnia lives, the water seems to turn reddish. The reservoir is simply teeming with this plankton. When the end of summer comes, the air and water temperatures drop, males appear and fertilize females, which produce eggs with a denser shell. These fertilized eggs are called ephippia. Their distinctive feature is their ability to withstand winter frosts and drying out of water bodies, and they can be carried with dust. With the onset of spring and warmth, females hatch from them, and life cycle repeats itself again.

Habitat

After we have learned what daphnia is, the habitat of these representatives of the planktonic genus should also become known to us, because probably many of those who read this article are lovers of pet fish and want to have such information. So, you can find these tiny crustaceans in stagnant bodies of water, for example, lakes, ponds, as well as water holes, ditches and even puddles. Often, places where they gather in large numbers are ideal for harvesting daphnia yourself. You can identify such a place quite easily: where daphnia lives, the water most often has a gray-green or reddish tint. Their food consists of ciliates, bacteria, and plant plankton.

Such different daphnia

Those wishing to catch daphnia themselves must take into account how sensitive they are to light. In bright light, crustaceans will try to go deeper. There are different types of Daphnia. The most common crustacean found in the middle zone is Daphnia magna. The female reaches a length of 6 mm, but the male is only 2 mm. They usually live 110-150 days and in one clutch they produce up to 80 eggs, which grow within 4-14 days. The smallest crustaceans reach only 1.5 mm in size and mature within 24 hours, but they have litters every 1-2 days, up to 53 eggs.

How are they good for fish?

Why do aquarium fish lovers always try to feed them daphnia? Everything is very simple. Regardless of whether these crustaceans are freshly frozen or freshly caught, their stomach is usually full of plant food, and this is so useful for aquarium fish that are deprived of a natural diet. This is why daphnia must be present in the aquarium. Despite the fact that the daphnia shell is not digestible, it serves as an excellent ballast substance. Thanks to it, the intestines of fish are activated, which are not able to fully move in the aquarium. For aquarium fish that have not yet grown up, representatives of the smallest daphnia - moina, popularly called "live-bearer" - are simply ideal.

If you plan to catch crustaceans yourself, you must take into account that where daphnia lives, there is a consistent change in the population of crustaceans. For fishing, a fabric net is used, the cells of which must correspond to the desired catch. Some experienced “fishermen” advise fishing with a net with very small cells, and only then sorting the food by size through a sieve with different cells. You can fish starting in spring until a crust of ice appears on the reservoir. For such an event, a coast protected from the wind is usually chosen in calm weather in the morning or evening. It is ideal if the lighting is dim. Then daphnia, the habitat for which will thus become favorable, will rise to the upper layers.

Breeding daphnia at home is a fairly simple task, but it requires care and patience. For this purpose, baker's yeast is usually used as food. You need to focus on the color of the water in the container where you breed crustaceans. The water should be greenish or light brown. If you notice that its color is becoming saturated, then you need to stop adding yeast for 1-2 days. Very soon the water should brighten again.

If breeding daphnia seems to you a very pleasant and interesting activity, be very careful and make sure that other inhabitants of reservoirs do not get into the vessel along with the crustaceans, especially cyclops. Get a magnifying glass and inspect the females' brood chambers every day. If they contain few eggs, then it is necessary to increase nutrition. Daphnia, whose home habitat is an aquarium or temporary container of water, can also feed on dried nettle or lettuce leaves. They are first ground into powder and then filtered through cheesecloth.

There is another simple way to breed daphnia at home. For this painstaking task, you will need a plastic or enamel bath, which must be half filled with water, and half-rotten hay and fallen leaves must be placed in it. Next, bacteria will begin to develop in this mass, which will become food for the crustaceans. Sometimes, in order to provide additional nutrition to the bacteria, a small piece of yeast is added to the water (approximately 15 g per 1 m 3 of water). This should be done every two weeks as the water becomes lighter.

And now the most important point: daphnia, whose habitat is usually a natural body of water, should end up in your vessel with the prepared food. To do this, 50 crustaceans are caught in about 100 liters of water in a standing reservoir and poured into a prepared container.

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Most often, daphnia is found in stagnant bodies of water - puddles, ponds, lakes, ditches, pits with water. Their massive quantity, suitable for independent preparation, can be detected by the coloring of the water red or gray-green. They feed on bacteria, ciliates and plant plankton, creating a flow of water using the movement of antennas.

When catching daphnia yourself, you need to take into account that they react strongly to lighting. When strong, they will tend to go deeper into the water, and when weak, upward or towards the light source.

Daphnia magna - larva about 0.7 mm, males 2 mm, females up to 6 mm. They ripen in 4-14 days. They produce up to 20 litters every 12-14 days. There are up to 80 eggs in a clutch. Life expectancy is 120 - 150 days. Cerio Daphnia reticulata - larva about 0.3 mm, males 0.5 - 0.8 mm, females up to 1.5 mm, mature in 2 - 3 days. They produce up to 15 litters every 1 - 3 days. There are up to 22 eggs in a clutch.

Life expectancy is 30 days. Moina rectirostris - larva about 0.5 mm, males up to 1 mm, females up to 1.7 mm. Ripen in 3 - 4 days. They produce up to 7 litters every 1 - 2 days. There are up to 53 eggs in a clutch. Life expectancy is 22 days.

Optimum conditions: dH 6-18 o, pH 7.2-8.0, temperature - 20 - 24 o C, CO2 up to 8 mg/l, weak aeration, light 14-16 hours a day. Under conditions of artificial breeding, crustaceans tolerate mineral fertilizers well (for example, up to 5 mg/l of phosphorus salts). They are fed daily with chlorella (200 thousand cells/ml) or baker's yeast (2 ml of suspension per 1 liter of water). You can use horse manure: 1.5 g/l, adding another 0.8 g/l every 10 days. In nature, the food spectrum is wider - green algae (endorina, angistrodesmus, etc.), bacteria.

Daphnia - Species

In the middle zone, the following types of daphnia crustaceans are most often found:
the largest Daphnia magna - female size up to 6 mm, male up to 2 mm, larva 0.7 mm, grows within 4-14 days, breeding interval 12-14 days, up to 80 eggs in one clutch, lives 110-150 days;
medium-sized crustaceans, Daphnia pulex, female up to 3-4 mm, breeding period 3-5 days, clutch up to 25 eggs, lives 26-47 days.
small crustaceans, up to 1.5 mm: species of the moina genera, female up to 1.5 mm, male daphnia up to 1.1 mm, daphnia larva 0.5 mm, matures within 24 hours, litters every 1-2 days, up to 7 litters , up to 53 eggs, lives 22 days.

The stomach of freshly caught or freshly frozen daphnia crustaceans is usually filled with plant food, so they are useful for feeding aquarium fish deprived of a natural diet.

The shell of daphnia, consisting mainly of chitin, is not digested, but nevertheless serves as a valuable ballast substance that activates the intestinal function of fish that are deprived of the opportunity to actively move in the aquarium. The smallest Daphnia moina, popularly known as Daphnia “livebearer,” is well suited for feeding grown-up juvenile aquarium fish.

Only Daphnia magna, Daphnia pulex, Daphnia mion can be bred by amateurs. But they also need care, proper maintenance, and nutrition. In this case, daphnia will fully reproduce and grow to become high-quality food for fish.

Finding daphnia for home keeping is not difficult: you can buy it or collect it from a pond. Ponds with waterfowl, lakes where there are few or no fish (both daphnia and diseases will be caught with fish), and containers with settled water are good for catching. The spoils at home are poured into a flat vessel, preferably white. This makes it more convenient to filter the future feed again, because... foreign organisms will settle to the bottom or attach to the white walls, where they are clearly visible.

If the collected crustaceans are used as food for fish, the water in which the live food lives is not poured into a common reservoir. Daphnia are selected with a net so as not to infect aquarium inhabitants. Daphnia Representatives of Cladocerans are kept in a shaded place, because They do not tolerate light well. Normal water temperature for life is in the range from 20 to 24° C (for the species Daphnia moin – 26-27° C), aeration is moderate to weak.

Plankton is fed: diluted baker's yeast, red meat water (meat juice, water washed off from it), chlorella. Yeast is frozen until brownish in color, 3 grams are diluted in 1 liter of warm water. yeast; this is the standard proportion. Meat water is given from 0.5 to 2 cm3 per liter of water. Instead of pure chlorella, you can simply add green aquarium water. To ensure that the fish have high-quality food, horse manure and ammonium nitrate are added to the food.

How to breed daphnia?

How to breed daphnia? A 15 liter plastic container or any other is perfect for growing daphnia. In this case, several recommendations can be noted: 1. It is necessary to avoid container materials that are soluble in water and emit harmful chemicals (certain types of plastic, in particular polypropylene);

2. If a metal container is used, it should not be made of stainless steel (some metals react slowly with water. Aluminum oxides form an oxide film, but some aluminum is released); 3. As in the case of a regular aquarium, a large surface area with air is required for gas exchange, because daphnia are very demanding of oxygen content;

4. If the container is located outdoors in strong sunlight or other lighting, it is recommended to use more than 40 liter volumes to make the water environment more stable. Additionally, when black aquarium material is used, it will heat up more than clear or yellow material, which should also be taken into account. For those who wish to have a small number of daphnia per week, the culture can be maintained in a two-liter bottle.

A good idea for growing daphnia in an aquarium is to connect the lighting via a timer, which can be purchased at an electrical supply store. It was found that Daphnia magna prefers weak aeration. In theory, aeration not only supports gas exchange, but also stabilizes water conditions and prevents inhibition of cultural development.

Daphnia pulex also likes light aeration. It is necessary to avoid small air bubbles that can get under the Daphnia carapace, raise them to the surface, interfere with feeding and ultimately lead to death (Artemia nauplii are also susceptible to this problem).

Catching

Catching Daphnia It all depends on the geographical location of the aquarist. The easiest to find are the most common Daphnia pulex and magna. For catching, it is necessary to choose lakes and ponds free of fish, because in the absence of the latter, more daphnia will be observed (due to the lack of predators) and, in addition, the absence of pathogens is guaranteed.

If the aquarist intends to catch daphnia from natural bodies of water, it is advisable to use a fine-mesh net or sieve (homemade from muslin fabric). Pass the net through the water evenly in a figure-eight motion, or scoop it up slowly. Do not allow the net cells to be too small and the water pressure to be too strong when catching, as this can lead to the death of the crustaceans.

Daphnia - Structure

A little more about the structure of daphnia. Aquarists use this name for various cladocerans. You can get an idea of ​​their appearance in the photo. In all representatives of daphnia, the body is strongly compressed laterally and covered with a chitinous bivalve shell fastened on the back. There are two eyes on the head, which in mature individuals can merge into one compound eye, and in some species there may be another additional ocellus next to it.

Also on the head there are two pairs of so-called antennas, the rear of which are large and additionally equipped with bristles that increase their area. It is due to the flapping of these antennas that daphnia move in the water. When stroked by the antennae, the body of the crustacean receives a spasmodic forward movement, for which daphnia received the second, popular name “water flea”.

Daphnia reproduces quite unusually from a human point of view. Female Daphnia have a cavity called the "brood chamber" located on their back and protected by the upper edge of their shell. In the summer, if conditions are favorable, unfertilized eggs are laid in this cavity, in the amount of 50-100 pieces. That's where they develop. Only females hatch from them and leave the chamber, and the adult female then molts.

A few days later the process is repeated. During this time, young female daphnia also grow up and become involved in the reproduction process. With a successful combination of circumstances, reproduction proceeds like an avalanche. This is why in summer, small bodies of water are often swarmed with daphnia, and the water appears reddish in color.

With a decrease in air temperature, at the end of summer and at the beginning of autumn, males begin to emerge from some of the eggs, they fertilize the females and they have eggs enclosed in a dense shell. They are called ephippia. They are able to withstand drying out and winter frosts, and can be spread with dust. Next spring, warmth and moisture will awaken them to life. They will hatch into females and the cycle will repeat.

BREEDING AT HOME.

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Daphnia

Daphnia are predominantly small crustaceans belonging to the Daphniidae family. This family, in turn, is included in Cladocera, which also includes Gammarus, Artemia and others. Due to its peculiar sudden movements it is often called a “water flea”. Not to mention the peculiarities of movement, daphnia is also similar in appearance to a flea. However, the latter belongs to insects and has a very distant common ancestor with crustaceans, since both classes are included in the phylum arthropods. All Daphnia species have different variations, and sometimes members of the same species are very different from each other. The characteristics of the phenotype, body size and shape depend on the area of ​​​​origin and specific environmental conditions. Representatives of the genus Moina have significant similarities with daphnia.

It is important to distinguish the Daphnia crustacean from other "water fleas" such as copepods, Cyclops species and barnacle crustaceans, which often live in the same places. Abrupt movements, body shape and, to a lesser extent, coloration are the best criteria for discrimination without the need for microscopic examination.

The genus Daphnia has a very wide distribution, including Antarctica, where Daphnia studeri, previously assigned to the genus Daphniopsis, was discovered in the relict salt lakes of the Vestfold oasis. At the beginning of the 20th century, the prevailing opinion was that most species had a cosmopolitan distribution, but it later became clear that the faunas of different continents differ greatly. Some species, however, have very wide ranges and are distributed on several continents. The smallest number of species is typical for equatorial regions, where daphnia are rare. The most diverse fauna is in the subtropics and temperate latitudes. In recent decades, the ranges of many species have changed due to human dispersal. Thus, a species from the New World, D. ambigua, was introduced into Europe. In many reservoirs in the southern United States, D. lumholtzi, which was previously found only in the Old World, has become common.

In ponds and puddles in central Russia, the following crustaceans of the genus Daphnia are often found, and therefore the most popular among aquarists. Daphnia magna (D. magna), female - up to 6 mm, male - up to 2 mm, newborns - 0.7 mm. They ripen within 10-14 days. Litters in 12-14 days. There are up to 80 eggs in a clutch, but usually 20-30. The lifespan of this crustacean is up to 3 months. Daphnia pulex (D. pulex), female - up to 3-4 mm, male - 1-2 mm. Litters in 3-5 days. There are up to 25 eggs in a clutch, but usually 10-12. Pulex live 26-47 days. In the lakes of the temperate zone of Eurasia, D. cucullata, D. galeata, D. cristata and several other species are often found.

Daphnia are small crustaceans, the body size of adult individuals is from 0.6 to 6 mm. They inhabit all types of standing continental bodies of water and are also found in many slow-flowing rivers. In puddles, ponds and lakes they often have high numbers and biomass. Daphnia are typical planktonic crustaceans, spending most of their time in the water column. Various species inhabit small temporary reservoirs, littoral and pelagic zones of lakes. Quite a few species, especially those inhabiting arid areas, are halophiles, living in brackish, saline and hypersaline continental water bodies. These species include, for example, D. magna, D. atkinsoni, D.mediterranea, as well as most species previously classified in the genus Daphniopsis.

They spend most of their time in the water column, moving in sharp leaps due to the flapping of the second antennae, which are covered with special feathered bristles. Many daphnia are also capable of slowly crawling along the bottom or walls of vessels due to water currents created by the thoracic legs; the antennae are motionless during this method of movement.

Perhaps the elusiveness of quickly jumping crustaceans reminded scientists of the legend about the nymph Daphne, who was almost overtaken by Apollo, but was never caught by him? Or maybe the mustaches of the crustaceans seemed to someone like the branches of an evergreen laurel into which a beautiful nymph had turned.

Ovid in his poem “Metamorphoses” told how once the golden-haired god of light Apollo carelessly laughed at Aphrodite’s son Eros (or, as the Greeks also called him, Eros). The offended god of love struck the silver-faced patron of the muses in the very heart with a golden bow. Having once met the beautiful Daphne, the daughter of the river god Peneus, Apollo fell in love with her at first sight, but the beautiful nymph, whom Eros struck with an arrow that kills love, began to run away from him with the speed of the wind. Then Apollo chased after her, but the nymph only ran faster and faster from the beautiful god. When her strength began to dry up, Daphne began to beg her father to deprive her of the appearance that brought her only grief. Old Penei took pity on his daughter. And at that moment, when it seemed that Apollo had already caught up with the beauty, she turned into a laurel tree.

The saddened Apollo did not want to part with his beloved. He decorated his quiver and cithara with laurel leaves, and placed a wreath of laurel branches on his head, the scent of which always reminded him of the elusive Daphne.

Reproduction in nature

During the summer months, daphnia are often found in blooming ponds and lakes that have high concentrations of algae. The fertility of daphnia is simply amazing, which is associated with the implementation of parthenogenesis.

Parthenogenesis is the ability of self-reproduction without the need for fertilization, when the offspring completely repeats the genotype of the parent, and any differences in the physiological state are determined by environmental conditions. Parthenogenesis allows daphnia to reproduce rapidly under favorable conditions, shortly after they emerge from the eggs. In nature, in late spring, summer and early autumn, depending on temperature, food availability and the presence of products of their metabolism, Daphnia reproduces parthenogenetically, giving birth to an average of 10 nauplii for each adult. During this period, only females are present in the reservoir. The developing embryo is often visible inside the mother's body without a microscope. Females of the next generation are capable of parthenogenesis after 4 days of development, with births occurring every three days. During her life cycle, a female can give birth 25 times, but in practice this number is slightly less and the female tends to produce no more than 100 offspring.

When there is a lack of food, some eggs develop into males, and females begin to produce eggs that must be fertilized. The latter develop into small embryos, which then go dormant and become covered with a dark brown/black saddle-shaped shell known as the ephippium. In this form, daphnia can carry harsh conditions environment, short-term drying out of the reservoir and even its freezing. Females born to form an ephippium are easily distinguished from parthenogenetic individuals because the developing ephippium is present in them as a black spot at the posterior end of the body. When environmental conditions become favorable again, a generation emerges from the eggs, which, in turn, gives birth to only females, while all males die before the onset of unfavorable conditions.

Fishing in natural reservoirs

They catch daphnia with a net. For this you need a special net - with a long handle up to 2-3 meters, usually made of several screwed sections, with a diameter of about 25-30 cm and a fabric cone about 50-60 cm long with a rounded end. The net ring is made of durable material, for example stainless wire with a diameter of 3-5mm. If you make it from a thinner one, it will bend easily, and considering possible snags on the bottom... But the most difficult thing is to choose the fabric for the net. Here, synthetic materials are preferable, such as nylon, which do not rot from prolonged contact with water. The mesh size of the net depends on what you are going to catch; very fine fabric greatly slows down the net in the water, so it is better to have several interchangeable rings with different fabrics for catching food of different sizes.

They operate the net calmly, smoothly, without much effort, moving it with a figure of eight in places where daphnia accumulate. We did it a couple of times, took it out, shook out the catch, and began to fish further. If you push a full net, many daphnia will crumple and die, so it is better to take it out more often with small portions of prey. Otherwise, greed, you know, does not lead to good. For fishing, it is better to prefer smaller bodies of water, for example, the same puddles - there daphnia are more accustomed to oxygen starvation and will more easily endure further transportation. True, it is difficult to catch in small puddles with a standard net; there you have to use a net with a shorter cone - otherwise it begins to cling to the bottom and create turbidity. In order not to catch hydra with daphnia, you should try to catch prey away from thickets of aquatic plants or objects in the water to which it can attach. And in no case is it recommended to catch food in water bodies where fish live - with such food you can easily introduce pathogens of various diseases.

The caught daphnia are placed in a container - a can or a special can for transportation. Before pouring, it is advisable to strain the catch through a thin mesh to remove any trapped debris and any large unwanted guests - swimming beetles or large dragonfly larvae. It is very desirable to have a battery-powered compressor in the transport container - it will keep most of the catch alive during the journey home.

At home, caught daphnia are poured into a wide flat vessel, for example a white enamel basin. There, for some time, all the unwanted organisms settle on the bottom and walls; on a white background, it is easy to spot the larvae of dragonflies and leeches, and everything else that has nothing to do with daphnia. There, at the bottom, dead crustaceans accumulate. When feeding, daphnia are caught with a net; the water in which they are located cannot be poured into the aquarium! These crustaceans are best suited for feeding small aquarium fish such as guppies or neons. For larger fish, it is more convenient to use live or frozen bloodworms.

In nature, daphnia live in ponds and large puddles, where they feed on various bacteria and phytoplankton. However, such reservoirs are often polluted industrial waste or they contain fish. Both can lead to diseases of aquarium inhabitants.

Daphnia can also pose a danger to aquarists themselves. In spring and early summer, the diet of crustaceans often includes pollen. flowering plants, carried by the wind into bodies of water. Daphnia caught at this time and dried for future use when feeding fish can cause a painful reaction in people suffering from pollen allergies. This fact, in particular, can explain the often-found opinion that an aquarium is harmful to health. In fact, the reason is pollen, with which crustaceans are literally “stuffed” during the period of mass flowering of grasses.

Breeding at home

A 15 liter plastic container or any other is perfect for growing daphnia. In this case, several recommendations can be noted. Avoid container materials that are water soluble or release harmful chemicals. If a metal container is used, it must be made of stainless steel. Aluminum oxides form a film, but some aluminum is still released. As in the case of a regular aquarium, a large area of ​​​​contact with air is required for gas exchange, because daphnia are very demanding of oxygen content. If the container is located outdoors, in strong sunlight or other lighting, it is recommended to use larger than 40 liter volumes to ensure a stable water environment. In addition, when black pond material is used, it will heat up more than clear or yellow material, which must also be taken into account.

For those who wish to have a small number of daphnia per week, the culture can be maintained in a two-liter bottle. For aquarium cultivation, a good idea is to connect the lights via a timer, which can be purchased at an electrical store. It was found that Daphnia magna prefers weak aeration. In theory, aeration not only supports gas exchange, but also stabilizes water conditions and prevents inhibition of cultural development. Daphnia pulex also likes light aeration. It is necessary to avoid small air bubbles that can get under the carapace of daphnia, raise them to the surface, interfere with feeding and ultimately lead to death.

The best nutrient medium for the culture is blue-green algae. Typically, these are free-floating species of green algae that tend to turn water into " pea soup", yeasts (Sacromyces spp and similar fungi) and bacteria. The combination of the above objects makes the process of maintaining the culture successful; yeast and algae complement each other.

Microalgae are consumed by daphnia in huge quantities, and an abundance of crustaceans is observed in places where water bodies bloom. There are a number of ways to ensure algae development that require minimal effort.

Placing the culture container in direct sunlight will ensure algae development within two weeks, usually sooner. Their spores are airborne and colonize water bodies, but, as a rule, some algae is added to the water to speed up flowering. Using plant fertilizers such as Miracle grow. Once a week, add 1 teaspoon of fertilizer to a 4-liter container. The container should be in direct sunlight. Aeration and slow movement of water are necessary. A system should be built according to which the first container with algae is already green, the second will acquire this shade within two days, the third within another two days, etc. When the first container becomes light green (after 2 weeks), it is poured into the daphnia culture. The empty container is refilled with the mixture with the addition of a small amount of water from the second container. Thus, every two days the aquarist has 4 liters of flowering water at his disposal, ready to be fed to daphnia.

The advantages of algae are the ease of preparation and the extremely rapid development of the culture of daphnia that consume them. There are no disadvantages, except for the need to constantly restart the tanks. Daphnia should not be placed in an environment that is too algae-rich because algae tend to raise the pH as high as 9. High alkalinity is associated with increased ammonia toxicity, even at low concentrations.

Baking, brewing and almost all other types of yeast are suitable for culturing Daphnia, but it is recommended to apply no more than 28 g per 20 liters of water as a daily rate. If you use yeast, you can additionally add algae to the water, which will prevent environmental pollution. It is important not to overdo it with adding yeast; excess will pollute the environment and destroy the daphnia culture.

Some baker's yeast comes mixed with active ingredients such as calcium sulfate, ascorbic acid, which stimulate the development of fungi. These components themselves are harmless to the culture, but ascorbic acid can lower the pH of the medium to 6, which is far from the ideal value for daphnia. This usually occurs when overfeeding.

The advantage of yeast as a nutrient medium is its ease of acquisition, and minimal effort in preparing and maintaining the culture. However, they are not as valuable from a nutritional point of view for daphnia as algae. Crustaceans need to consume large mass yeast than algae for the same nutritional value.

Daphnia lives in a wide range of temperatures. The optimal temperature is 18-22 C. D. pulex thrives at temperatures above 10 0C. Moina can withstand even harsher fluctuations, 5-31 C; the optimum is 24-31 C. Moina's increased resistance to temperature makes it a preferred cultivation object when the optimum for D. magna under natural conditions is reached only once a year.

Daphnia are tolerant of dirty water, and dissolved oxygen levels can vary from almost zero to super-saturated. Like Artemia, Daphnia's ability to survive in oxygen-poor environments is due to its ability to form hemoglobin. Hemoglobin production may accelerate with increasing temperature and population density. Just as in the case of artemia, daphnia does not tolerate active aeration with small air bubbles, which can destroy it.

Producing daphnia is a relatively easy process. However, there are measures to increase cultivation productivity. Good aeration, good to the extent that the water is saturated with oxygen, but not excessively strong aeration, is the main factor in increasing productivity. Some species prefer the absence of aeration, but Daphnia magna grows better in its presence. In addition, this makes it possible to increase the density of the culture; water circulation reduces algae deposits on the walls of the vessel, and also transfers food particles into suspension, which is typical for the natural diet of daphnia. The only drawback is that small air bubbles fill the carapace of the crustaceans, which float up and cannot feed. Air spray should be avoided altogether, or it should be very rough to create large bubbles. Convenient in terms of aeration is the “bio-foam” filter. It is usually used in an aquarium with fry, but is ideal for daphnia. It captures large particles and helps them break down to feed algae.

Regular selection/collection of culture. This event maintains constant growth of the crop and provides daphnia with the opportunity to quickly accumulate oxygen and food. A 24-hour daylight period increases the productivity of daphnia, but this is not a necessary measure. Also, you should not keep daphnia in the dark for 24 hours, because this stimulates the crustaceans to form ephippia. The mode and degree of water replacement depends on the nutrient medium used, but, in any case, they are necessary for purification of metabolites and toxins.

When it comes to cultivating daphnia, collecting them can be a real challenge, but it is an integral part of the entire breeding process. Otherwise, overpopulation becomes a serious problem. Even if you have to shake the crustaceans into the sink, this must be done because the culture can become unstable. If the aquarist cultivates daphnia at temperatures below 25 0C, it makes sense to start catching in the middle of the second week. This is because most crops take several days to adapt and begin reproducing. When culling/catching, a net is used that has cells large enough to allow young crustaceans to pass through, but small enough to catch adults. Some aquarists recommend pouring ¼ of the container through the mesh and then filling the volume with a new portion of water with nutrient medium. No more than ¼ of the population can be caught daily, which also depends on the quality of cultivation. Catching can be done during the day when aeration stops, when all daphnia rise to the top layer of water.

Caught crustaceans can live for several days in a fish tank with fresh water. They show normal activity when the temperature rises. However, the nutritional value of daphnia gradually decreases because they are starving and must be provided with food for the best effect. Crayfish can be stored frozen for a long time if they are frozen in water with a low salt content (0.007 ‰, density - 1.0046). Of course, this will kill the daphnia, due to the leaching of nutrients their value will decrease, almost all enzymatic activity will be lost within 10 minutes, and after an hour ½ of the free amino acids and all bound ones will be lost. Fish are not so willing to eat frozen crustaceans.

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The body of daphnia is compressed from the sides and everything is covered, except for the head, with a bivalve shell (carapace). Inside the shell, the body is placed freely, attached to it only by the front part.

Between the walls of the shell valves and the dorsal surface of the animal, females have a brood (embryo) chamber. The edge of the shell on the dorsal side is elongated into a long spine (spina). The head is bent on the ventral side, the frontal part is extended into the rostrum directed downwards and backwards. The large median eye, formed by the fusion of the embryonic two compound eyes, is equipped with special muscles that determine its mobility inside the ocular chamber. Some species of Daphnia also have a small unpaired eye. The short antennules, which are sensory organs, are articulated in females motionlessly with the head behind the rostrum; at the end they bear a tuft of sensitive bristles.

The antennae, which are the only organ of movement, are well developed, consisting of a large protopodite and two branches, the outer, or exopodite, and the inner, or endopodite, armed with long feathered swimming setae. Strong muscles are visible inside the antennae. Each antenna is driven by three abductors, three adductors and one levator; The first two abductors and the levator are attached to the chitin of the dorsal part of the head with their conspicuous fan-shaped extended ends. The antenna rises due to contraction of the adductors and levator, the abductors being their antagonists.

The mandibles, clearly visible in living organisms by their peculiar movements, lack a palp and have a large chewing surface on the inner side, consisting of chitinous plates armed with spines. The maxillae are reduced. Maxillae are completely absent. There are a total of five pairs of thoracic legs, which are turgor limbs.

On the dorsal side of the abdomen (abdomen) there are several abdominal outgrowths that serve to close the brood chamber at the back; behind these processes there is a pair of feathered swimming or caudal setae. The posterior section of the abdomen behind the caudal setae is called the postabdomen, or cauda. It is bent under the body of the organism so that its upper, or dorsal, edge, on which the anus opens and the anal denticles are located, becomes, as it were, the lower edge; at the end of the postabdomen there is a furca, formed by two strong and slightly curved claws, called furcal, or caudal, claws.

The mouth, bounded above by the upper lip and on the sides by mandibles, leads into a short esophagus, which passes into a long midgut, of the same diameter along its entire length; in the anterior part of the midgut there are paired hepatic outgrowths, which look like short and curved blind appendages located in the head.

The heart looks like a round sac with one pair of lateral spines. Heart contractions occur with great speed, at room temperature - up to 200-290 beats per minute, which is the limit for animals. Blood from the heart enters the lacunae of the body. The osmotic pressure of blood under normal conditions is two to four atmospheres. This circumstance is of great importance for maintaining the shape of the body and the elasticity of the limbs (turgor limbs).

The respiratory organs are the epipodites of the limbs, which are washed by currents of water caused by the rhythmic movements of the legs.

The excretory organs are paired armored (shell) glands located in the thickness of the shell valves, between the outer and inner layers, and are clearly visible after the valves are separated from the body of the daphnia.

The clearly visible brain consists of two fused halves. Nerves extend from its anterior part to the compound eye, and on the underside there is often an unpaired (nauplii) ocellus.

The reproductive organs of females extend along the sides of the intestine from the first pair of legs to the post-abdomen; short oviducts open on the dorsal side of the body at the rear of the brood chamber.

All embryonic development of the juveniles takes place in the brood chamber during the period between two molts. Daphnia produce parthenogenetic and latent eggs. The latter are enclosed inside the highly modified and dark-colored upper part of the shell valves, forming the so-called ephippium (saddle).

Daphnia males differ from females in the absence of a brood chamber, the presence of large and mobile antennules, and different armament of the legs of the first pair.

A—B—Daphnia magna, female (A), male (B), female postabdome (C), D, E—Daphnia longispina, female (D), female postabdomen (E); B - Dap cucullata, female; F, 3 - Daphnia cristata, female (F), antenna (3).

The five most common species of Daphnia differ from each other in the following characters.

The caudal claws are armed with large spines at the base.

The upper (dorsal edge) of the postabdomen is straight, without a notch - D. pulex

Upper edge of postabdomen with notch - D. magna

The caudal claws at the base lack large spines

There is an unpaired eye - D. longispina

The gypsy eye is absent

The rostrum is sharp, the setae of the antennules do not extend beyond its end - D. cristata

Rostrum obtuse, setae of antennules extending beyond its end - D. cucullaia

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