Danio pink disease and treatment. Danio pink disease. Prevention of possible health problems in zebrafish

Danio diseases: prevention and treatment

Under optimal conditions of maintenance and care, unpretentious viable zebrafish practically do not suffer from diseases.

The best preventive measures are:

• systematic weekly change of 20-25% of water,
• constant aeration,
• uninterrupted operation of bottom filters,
• regular, dosed and varied feeding.

Therefore, food must be purchased from trusted sellers and carefully reviewed before use in order to distinguish and remove third-party harmful components.

Plants, like soil, must be kept in a solution of potassium permanganate before being placed in an aquarium, and then rinsed.

Acquired fish should be observed for 3-4 weeks in a separate quarantine vessel before being placed with the rest.

However, despite precautions, zebrafish can suffer from the following diseases:

• Pleistophorosis. On the body of the fish, gradually growing, whitish spots appear. The dorsal and caudal fins are disheveled and pressed, the tail falls down, so that the zebrafish swims at an angle of 45-60 degrees, constantly trying to assume a normal position. The fish is emaciated, trembling and suffering from ulcers. In this case, obviously sick zebrafish should be destroyed, the soil removed, and the aquarium should be disinfected with bleach or a five percent solution of hydrochloric acid. Surviving inhabitants can be treated with food. To do this, erythrocycline (50 mg solution in one liter of water) or griseofulvin (10 mg/l), trichopolum (5 mg/l) or methylene blue (10 mg/l) are added to the usual dry feed mixture. Fish whose condition worsens during treatment are also destroyed.
• Trichodinosis. Disease due to the reproduction of pathogenic ciliates. Danio begins to rub against hard objects and plants. The color of the fish fades, a grayish coating appears on the body, which is separated by flakes. Treatment consists in enhanced aeration of the aquarium with an increase in water temperature to 31 degrees, as well as the gradual addition of a solution of table salt in the amount of 1 tablespoon per 10 liters of water. This concentration is maintained until the zebrafish fully recovers within 7-30 days, and then salinity is eliminated by regular water changes.

For all other disease states, the following general rules apply:

• clouding of the eyes, damage to the fins, mucus on the gills and discoloration, tarnishing and spotting of color can be cured by regular five-minute baths in a solution of methylene blue (3 ml of a 1% solution per 10 liters of water) at a temperature of 30 degrees.
• Conditions with loss of balance, bulging eyes and tumors on the gills and skin are incurable.

Lifespan

In an aquarium, small species of zebrafish up to 5 cm in size, with proper care, live 3-4 years. Larger, ten-centimeter varieties live 5-7 years.

average price

The cost of aquarium Danios depends on the rarity of the species. The most common Danio rerio cost from 21 rubles per copy. Fluorescent fish cost 29 rubles apiece, and Danio firefly is sold for 137 rubles.

reproduction

Sex differences

A common feature by which females can be distinguished from males is body size and degree of fatness. Males are somewhat smaller and slenderer than females, they have a smaller abdomen, and the color is usually brighter. In addition, some species have additional color nuances that allow you to reliably distinguish the sex of the fish:

• Malabar zebrafish - the ventral and anal fins of the male are bright pink, the female is pale, pinkish.
• Danio firefly - the dorsal stripe is orange in males, and yellow in females.
• Burmese zebrafish - an orange stripe runs along the anal and ventral fins of males. In females it is white.
• Spotted zebrafish - the female's abdomen is orange, the male's is white.

Fry

Juvenile Danio develops rapidly, going from egg to larva in no more than 3 days. In the larval stage young growth hangs on glass, substrate and plants, in a day it begins to swim freely and actively eat microscopic food. In the practice of aquarium fish farming, the following methods of feeding young fry are used:

• Feeding ciliates-shoes propagated on hay or banana peel. The process is time consuming and requires skill.
• A treat with a few drops of water suspension crushed boiled yolk. At the same time, it is necessary to carefully monitor the purity of the water in the aquarium: the uneaten yolk quickly deteriorates. This method of feeding is used as a temporary or auxiliary.
• Nutrition with specialized food for juvenile aquarium fish, frozen plankton. Then, as they grow, use dry food for fry.

Receiving offspring

Under natural conditions, Danios breed in shallow water, at night and in the early morning hours.

To ensure productive spawning, prepare a separate aquarium with a capacity of 20-30 liters. A substrate is placed at the bottom, which will serve as a shelter for the eggs, since after spawning, the producers willingly eat them. The protective bottom cover can be

• fine mesh;
• small stones;
• glass balls;
• undersized small-leaved aquatic plants - Riccia, Javanese moss.

The breeding aquarium is half filled with water, an aerator, a heater and a low-power sponge filter are installed in it.

Danio is prepared for spawning: they raise the temperature of the content to the upper norm (24-25ºС), maintain a neutral water reaction and provide abundant protein food, consisting of live or frozen daphnia, artemia, and bloodworms.

Females ready for breeding can be distinguished by a rounded abdomen, and males by a particularly bright color. The best producers are planted in a prepared separate aquarium for spawning. At the same time, there are 2-3 males per female. The water in the spawning ground should also be heated to 24-25 degrees. Then, to stimulate the beginning of spawning, cool fresh water is gradually added, by the evening, reducing the temperature of the aquatic environment to 20ºС. Spawning in this case occurs at night, and in the morning the producers should be returned to a regular aquarium. The temperature in the spawning ground is raised to 28 degrees to speed up the release of the larvae from the eggs.

• Easy to care for, Danio rerio has become a favorite model object for geneticists. Large translucent rapidly developing embryos of this fish are very convenient for genetic manipulations. Intensive reproduction with a rapid change of generations (Danio rerio is capable of spawning already at the age of six months) is an additional plus for those who experiment with heredity.
• As a result of the fluorescent rerio-GloFish can be considered the first ever publicly available genetically modified pet.

Photo and video

Often one of the reasons for the disease of fish is their improper maintenance, so you need to carefully monitor aquarium fish. If the fish grow in adverse conditions, then they become unarmed to infectious diseases. Often the fish get sick due to low water temperature and insufficient oxygen content in the water.

Also, one of the reasons for the disease of fish is improper feeding. Starvation for adult fish practically does not harm them, but for fry this is a big minus. In the first days of life, fry need to eat well in order to grow. Overeating for adult fish causes obesity, which later leads to their death, since obesity is not treated. Feeding a monotonous diet can lead to inflammation of the stomach and intestines. With such a disease, the appetite, as a rule, does not disappear in the fish, but their color becomes darker, and their movements are more constrained. Inflammation of the stomach and intestines in fish weakens them, and this is a big chance that the fish will catch infectious diseases.

How to cure fish?
1. When adverse conditions of detention, improper feeding and in case of injuries to fish, the only treatment is to create optimal conditions for the fish.

Curable diseases: clouding of the eyes of the fish, damage to the fins, mucus on the gills, discoloration of the gills, fading of the color of the fish - all this is treated with short-term, but repeatedly repeated baths (water 30-32 ° C with a high concentration of methylene blue). They also use baths if the fish move a little, are covered with all the various specks or spots. In the intervals between baths, fish are kept (as already described above) in a separate vessel.

Incurable diseases:
If a fish loses its balance and swims with its tail down or sideways, then such a fish is incurable.
Bulging of one or both eyes is incurable.
Tumors on the gills and skin of fish are incurable.

Danio diseases, as well as the causes of their occurrence, will become the main topic of today's conversation. One of the most common aquarium inhabitants can rightly be considered such a fish as.

It is a very unpretentious and popular species, easily recognizable by several horizontal dark stripes running along the body, as well as by its tendency to live in small groups. And with its unpretentiousness, yet this friendly and sociable fish, like any other species, has a tendency to a number of diseases. So, let's begin.

It is a very small relative of the well-known carp. These fish live in the reservoirs of the southeastern corners of Asia.

It is small, about 6-8 cm long. a fish with an elongated body flattened on the sides, the color of which ranges from white to red, and the main external attribute is horizontal stripes along the body. This is a gregarious species, usually adhering to a company of 6-8 individuals.

Prevention of possible health problems in zebrafish

As befits zealous owners, we begin to take care of both the new pet and those residents of the aquarium that we already have, from the very moment we purchase the zebrafish.

It is very important first of all to carefully examine the skin of the fish, in order to make sure that there are no signs of disease or mechanical damage on the body and fin system.

Do not panic if the zebrafish looks too pale, as this may be a consequence of fright from the handover process. It would also be a reasonable precaution to settle the zebrafish in a separate container immediately after the purchase in order to observe its behavior, and only if you are sure that the fish is in a healthy state, you can safely add it to a common aquarium.

Danio has quite reliable health and is quite resistant to diseases. And this is one of the reasons for its popularity among beginners in the aquarium business, because it is really very unpretentious in care.

However, one of the first requirements for its healthy maintenance is the need for artificial aeration of the air inside the aquarium and its high-quality filtration. You can not mention the timeliness of changing the water in the aquarium, since this iron rule is equally significant when keeping almost all aquarium fish.

Also, zebrafish is quite demanding on such a characteristic of water as the level of its acidity. Its value should fluctuate within 6.5-7.5. We will talk about the possible consequences of deviating this parameter from the norm.

Just like the unshakable rule is the inadmissibility of regular overfeeding of fish. After all, it is known that most diseases of both zebrafish and other aquarium fish most often occur when the metabolism of our wards is disturbed.

This is a very important point and the determination of a healthy daily and single dose when feeding zebrafish should be considered first.

And do not forget to sterilize with boiling water everything that we put in a tank with fish, be it artificial decorations, pebbles or driftwood.

Diseases of zebrafish

Now, actually, about the main thing.

The most frequently encountered include the following:

• bulging eyes;
• obesity;
• trichodinosis;
• growths on the body;
• tuberculosis;
• alkalosis.

bulging eyes

Bulging is the most common disease that zebrafish suffer from. The reason for its occurrence is unsatisfactory water quality.

Usually the disease affects the fish during spawning, and it is not always possible to track the onset of symptoms, since one of these is an increase in the abdomen, which can be mistaken for pregnancy in the female.

A few weeks later, a more serious symptom of the disease appears, thanks to which it got its name. The eyes of the fish bulge and eventually fall out, which eventually leads to death.

Obesity

Obesity is a consequence of overfeeding, the prevention of which was discussed earlier. And if we see an increase in the zebrafish's abdomen, this is of course not a reason to immediately sound the alarm, but it means that it is already necessary to look at the fish. It is possible that there is a metabolic disorder.

Prevention is important here, once again we remind you of the rule - it is better to underfeed the fish than to overfeed.

Trichodinosis

Trichodinosis is already an infectious disease caused by trichodin ciliates.

It occurs as a result of poor-quality disinfection of objects placed in the aquarium. When this disease occurs, the fish often begins to rub against the walls of the aquarium, the shade of the skin also changes, it becomes pale, a dirty coating on the body is noticeable.

As a treatment, the water temperature should be raised to 30 degrees, it is also necessary to use tripaflavin or table salt as baths as part of quarantine.

growths

Growths on the body of zebrafish, in principle, occur infrequently.

However, sometimes this is the case, and in this case, the fish should be removed from the general tank to a quarantine tank, where salt baths should be used at a temperature of 28 degrees. The problem should quickly disappear.

Tuberculosis

Yes, it can even suffer from such a dangerous disease as tuberculosis or mycobacteriosis.

Another infectious disease of fish that can be brought into the aquarium along with soil, algae or other infected fish. The most common symptoms include lethargy, lack of appetite in the fish, and even loss of scales.

A very dangerous disease that can be treated only in the initial stages. The main drug for fish tuberculosis is kanimicin.

It must be mixed with food in a ratio of one to one, that is, 15g. feed give 15 gr. medicinal product.

Mandatory is the quarantine of a sick individual in a separate tank. At the same time, after the end of the treatment, whatever its outcome, it is imperative to carry out a general cleaning and cleaning of the common aquarium with disinfection of all decorative elements.

Alkalosis

Alkalosis or alkaline disease. This disease occurs when the acid-base balance of water is not observed.

They are sensitive to this parameter, and therefore, if your pet shows noticeable anxiety, often jumps out of the water, itches on the bottom or walls of the aquarium and she has a blanching of the skin - all this can be just signs of alkalosis.

To eliminate this problem, you should purchase a pH buffer, which will further maintain the acidity of the water at the desired level.

Conclusion

Thus, we have learned everything you need to know about the most common diseases in zebrafish. As well as got acquainted with their few needs and conditions for the proper maintenance of these wonderful creatures.

It is really unpretentious and caring for it should not be a problem even for a novice aquarium fish lover.

Danio - fish that appeared in my aquarium thanks to dad. This is after I swapped my gouramis for neon ones. Out of a dozen danios of two species (striped and pink), 5 pieces are now left. We need to think about buying more or just try to breed these funny fish. But that's in the future. I decided on this page to collect the most complete information about aquarium zebrafish, along with my photos and not my videos

By the way, zebrafish are quite agile fish and it was extremely difficult to photograph them. In general, I would not really like to have such fish rushing around the aquarium in my relaxing pond. But my father decided otherwise.

Danio (lat. Danio) is a genus of small ray-finned fish of the carp family, some species are common in the aquarium hobby. They inhabit reservoirs with stagnant and running water in Southeast Asia. The most popular in the aquarium hobby is the zebrafish.

The zebrafish is a model organism in developmental biology and is known in the English language literature as the zebrafish. Zebrafish is the first pet genetically modified with bioluminescence genes in 2003 (GloFish)

GloFish is a proprietary commercial brand of GloFish that sells genetically modified fluorescent fish; originally they were zebrafish (lat. Danio rerio) - a type of unpretentious and popular aquarium fish of the carp family. Genetically bred GloFish individuals are distinguished from their original form by a red, green or orange fluorescent coloration that becomes more visible and intense under ultraviolet light. Although not originally bred as ornamental fish, they became the first genetically modified pets available to the public.

Transgenic zebrafish differ from their original form in body color. DNA fragments of jellyfish (lat. Aequorea Victoria) and red coral (from the genus lat. Discosoma) are built into their DNA. Zebrafish with a jellyfish DNA fragment (GFP gene) are green, those with coral DNA (RFP gene) are red, and fish with both fragments in their genotype are yellow. Thanks to the presence of these foreign proteins, the fish glow brightly in ultraviolet light.

The transgenic form prefers warmer water - about 28 °C. Maintenance, feeding or differences in breeding and development of genetically modified Danio Rerio have not been noticed: transgenic fish are also unpretentious in maintenance and peaceful.

History of GloFish

The natural zebrafish from which GloFish was grown lives in the rivers of India and Bangladesh. It has a size of about three centimeters in length and gold and blue stripes located along the body. Over the past 50 years, these fish have been sold in the US ornamental fish market for over $200 million, but despite this, no one has been involved in their reproduction in the US, primarily because they are tropical fish and cannot exist in temperate North American climate.

In 1999, Dr. Zhiyuan Gong and his colleagues at the National University of Singapore worked on the green fluorescent protein (GFP) gene, which nature has endowed only in some Pacific jellyfish. This gene is responsible for the synthesis of a phosphor protein, which emits rays of a pleasant greenish color in the dark. They inserted this gene into a zebrafish embryo, creating a genome that gave the fish bright fluorescent colors from both natural white light and ultraviolet light.

The original goal of genetic engineers was to make it easier to observe the internal organs of these translucent fish. But a photo of a fish glowing with a greenish ghostly light, shown at a scientific conference, was seen by a representative of a company that breeds and sells aquarium fish. At the request of the company, another red glow gene isolated from sea coral was added to the zebrafish genome. The resulting breed was named "Night Pearl".

In the United States, luminous zebrafish were originally obtained in order to create living indicators of pollution: in the presence of certain toxic substances in the water, the fish had to change color. But in 2003, businessmen and scientists entered into a contract, according to which the first genetically modified GloFish fish appeared on the market.

In addition to the red fluorescent zebrafish sold under the brand name Starfire Red, green and orange-yellow fluorescent zebrafish were introduced by mid-2006, followed by blue and purple zebrafish in 2011. These fish lines have been traded under the trade names Electric Green, Sunburst Orange, Cosmic Blue, and Galactic Purple. .Galactic Purple). All of these fish have been genetically engineered using recombinant DNA from various marine corals.

In 2012, a new variety of fluorescent aquarium fish appears under the brand name of the green variety of the English. "Electric Green" GloFish, which were bred by the same method as the previous ones, but instead of zebrafish, ordinary thorns (lat. Gymnocorymbus ternetzi) were used. In 2015, luminous green Sumatran barbs (lat. (Puntius tetrazona)) were introduced.

Despite the widespread opinion about the sterility or sterilization of genetically modified fish in order not to spread them in natural water bodies, it is possible to get quite healthy and viable offspring from GloFish. and the sale of GloFish fluorescent fish is strictly prohibited.

The sale and possession of GloFish remains illegal in California due to an ordinance restricting the farming of any genetically modified fish. The regulation was introduced prior to GloFish sales, mainly due to concerns about the biotechnology of fast-growing salmon. Although the Fisheries Commission refused to grant an exemption (on ethical grounds) in December 2003, it subsequently reversed course and decided to move forward with the goal of deregulating GloFish.

Canada also bans the import and sale of GloFish due to lack of sufficient information to make a safety decision.

Within the European Union, the import, sale and possession of these fish is not permitted. However, on November 9, 2006, 1,400 fluorescent fish were found by the Dutch Ministry of Housing, Spatial Planning and the Environment, which are sold in various stores from aquariums

But back to the zebrafish. Danio rerio is a model organism that is used to study vertebrate development and gene function in vertebrates. Early work by George Streisinger at the University of Oregon showed the potential for using Danio rerio as a model organism; the importance of this model has been confirmed by many genetic studies. Danio rerio is one of the few fish species that have been on an orbiting space station.

As a subject of developmental biology, Danio rerio has some advantages over other vertebrates. The embryo develops quickly, going from egg to larva in just three days. Embryos are large, hardy, strong, transparent and develop outside the mother, which facilitates manipulation and observation.

Antisense Morpholino technology is often used to turn off genes or change splicing in Danio rerio. Such oligonucleotides are synthetic macromolecules containing DNA or RNA nucleotides that bind to complementary RNA sequences and reduce gene activity. Morpholino oligonucleotides can be introduced into embryonic cells after the 32 cell stage, resulting in an organism in which gene activity is reduced only in those cells derived from the modified cell. Although cells of the early embryo (less than 32 cells) are impermeable to large molecules, they allow Morpholino molecules to penetrate between cells.

On January 23, 2013, Spanish scientists conducted an experiment to introduce the hoxd13 gene, borrowed from four-legged mice, into the fish genotype. Fish have a similar gene, but do not show sufficient activity. As a result of the experiment, the fish received the rudiments of limbs suitable for movement on land.

Danio species from kwitri.ru

The most common species in modern aquariums remains zebrafish, or zebrafish. As in other species, the female has a more rounded abdomen. Often there are veil forms. The body length of the fish is up to 7 cm.

They are very similar in color and size. The main difference is the orange stripe that runs from the middle of the body to the tail fin of the pearl zebrafish. The body length of the fish is up to 6 cm. This species looks more advantageous with the right lighting. The fish reach sexual maturity at eight months.

Leopard zebrafish got its name for the corresponding color - there are many irregularly shaped dark-colored spots on the body. The body size of the fish is up to 5 cm.

Danio orangefin- got its name because of the color of the fins, their edges are painted yellow-orange. In mature males, the coloration is more pronounced. The body length of the fish is up to 5 cm.

Danio firefly, or danio chopra - a small (up to 3 cm in length), bright fish, painted in orange-yellow tones. The caudal fin appears to be bifurcated due to yellow-colored outer rays, while the central part remains transparent. Along the crest of the back from the head to the dorsal fin there is a luminous strip, and in females it is yellowish, in males it is reddish. In mature females, a bright orange stripe runs along the body.

Danio dangila, or olive - a rather large representative of the family, its body length is up to 10 cm. The body is covered with a peculiar ornament, a distinctive feature is a large dark spot behind the gill cover. This species is undesirable to keep with fish that have veil fins, since in a flock these danios can peel off these very fins. In general, this species (when kept in a flock) is quite aggressive; zebrafish dangila can attack larger fish.

Danio erythromicron, or ribbon microassembly, emerald - a small fish (2.5 cm) of a very original color. A distinctive feature of this danio is no mustache. Peaceful, shy fish, so vegetation in which they could hide is very desirable in an aquarium.

Danio Burmese, or fagradei - fish with a delicate color: golden specks are scattered over the blue body. Behind the gill cover is an orange spot. Males have an orange stripe on their anal and pelvic fins, while females have a white stripe.

Danio blue, or kerry - a fish with a catchy color: two sparkling pink stripes run along the olive-blue body. The male is smaller, slimmer and brighter, the color of females is dominated by gray tones. The body length of these fish is up to 5 cm. The view is peaceful.

Danio Malabar- the largest representative of the genus. The body length of the fish in the aquarium is about 10 cm. The color is very interesting: along the body, slightly receding from the head, 3-4 shiny, longitudinal bluish-turquoise stripes stretch, separated by golden stripes. Immediately behind the gill cover there are several transverse golden strokes and specks of the same color are scattered throughout the body of the fish. In the male, the middle longitudinal blue stripe continues in the middle of the caudal fin, while in the female it passes to the upper lobe. The view is peaceful. These zebrafish reach sexual maturity by one year.

Danio fluorescent, or Danio GloFish - p The fish, according to the conditions of detention, is no different from the original species - zebrafish - unpretentious, schooling and mobile for the upper layers of water in the aquarium.

Danio Bengal- a peaceful, unpretentious, schooling fish with a body size of 7-8 cm. At the level of the dorsal fin, 3 blue longitudinal stripes begin on the lateral part of the body, separated by yellow lines, which merge into one strip on the caudal fin, passing to its upper lobe. Of all the zebrafish, this species has the longest dorsal fin. Males, like other species, are more graceful and brightly colored.

Danio point- the color of the upper body resembles zebrafish: the same dark stripes on a light background. The lower part of the body and the anal fin are not covered with stripes, but with dark dots. There are also dark stripes on the caudal fin. The length of the fish is not more than 4 cm. The male is smaller than the female, his abdomen is white, the female's is orange. The view is peaceful. For this species, the water temperature should not be lower than 24 ⁰С.

Danio margaritatus, or microsorted galaxy - the brightest representative of zebrafish. These fish begin to acquire their bright color at the age of two months, and by six months they are completely colored. These fish are very beautiful, but their extreme fearfulness prevents them from admiring enough. An aquarium with them must be planted with plants so that the galaxies feel calmer. These fish are kept in large flocks of 20 or more individuals. The water temperature for them should be no higher than 26⁰С, preferably 22-24⁰С.

Since in the event of danger approaching, these fish can jump out of the water into the air so that the pet is not lost, the aquarium should always be covered with a lid. The optimal distance from the water to the lid is approximately 3-4 cm, so that when jumping out, the fish does not hit a hard surface and does not get hurt.
Keeping zebrafish and caring for them at home is quite simple. Fish mainly swim in the upper layers of the water, where oxygen is the most. In this regard, you do not need to install additional aeration of the aquarium.
Danio rerio live in groups. Therefore, if you decide to purchase them, buy 8-10 individuals at once. Since the size of these fish is small - about 4 - 5 cm, an aquarium with a volume of 6 to 7.5 liters is quite suitable for their comfortable living. The optimum water temperature for zebrafish should be around 24°C. Although these fish will react quite calmly to its slight changes.
If you want to breed zebrafish yourself, then you need to prepare another aquarium - a spawning tank. The water thickness in it should be no more than 6-8 cm. After spawning, the female and male are seated in different aquariums, after which, after 7 days, the female is again launched for re-spawning in order to avoid her infertility.
Feeding zebrafish is also an important process. For this, dry or live food suitable for this species is suitable. It is very important that the food is crushed, otherwise the fish will not be able to swallow large pieces.

Zebrafish compatibility with other fish

If you have replenished your home living area with these beautiful aquatic inhabitants, you can be calm, because zebrafish get along well with most types of aquarium fish. They get along well with catfish, tarakatums, neons, tetras, gouras, laliuses, swordtails, ancistrus, platies, iris, rasboras, mollies, bots, guppies, cockerels, scalars, catfish Corydoras and labeo. Also, "danichki" get along quite well with snails, shrimps and snails.
Despite the good compatibility of zebrafish with other fish, there are some warnings. If you have a barb or some other type of more aggressive fish living in your aquarium, do not place a veil zebrafish with them, because. more nimble occupants may damage or bite off their veil and long fins.
You can not keep zebrafish in the same aquarium with goldfish, eels, cichlids, astrotonus, discus and Koi.

Diseases of zebrafish

Unfortunately, despite all the charm and unpretentiousness of these fish, they have one flaw. This is a congenital zebrafish disease that appeared from breeders - a curvature of the spine. The main symptoms are raised scales, gills splayed to the side and slightly bulging eyes. Most often they all appear after a fright. A few days later, the central vertebra begins to bend in the zebrafish, and as a result, after a while the fish dies.
A well-known disease of zebrafish is also dropsy. Fish have rearing scales, eyes bulge, belly swells and eventually death occurs.

How to distinguish zebrafish? Male or female zebrafish?

The site kakprosto.ru has instructions on how to distinguish a female from a male zebrafish. I'll bring it here.

Only adults can be distinguished from each other by gender, since young fish are not yet sufficiently formed and are very similar to each other. If gender matters to you, be sure to purchase only adult, fully formed fish, only in this case you can more or less accurately determine which of them is male and which is female. Also make sure that all the fish in the tank are the same age, as this greatly affects their size. Young females can easily be mistaken for males when compared with older fish.

The most accurate criterion for determining the sex of Danio fish is size. Look at a school of fish and try to compare them with each other. Females are usually larger and have a rounded abdomen. Males, on the other hand, are distinguished by a slender physique and are a little short of the size of their girlfriends. This structural feature is associated with the ability to produce caviar and bear fry, which directly depends on the size of the zebrafish female.

Pay attention to the intensity of the color of the fish. The stripes on the body of females are paler and less noticeable, and zebrafish boys are usually brightly colored and shimmer very distinctly. This coloration is evidence of good camouflage of the fish. Pregnant females are more clumsy and slow, so they should not stand out in the sea thickets or against the background of the bottom.

Zebrafish breeding

The aquavitro.org website describes in great detail about zebrafish breeding. I'll post the article here.

Most of the research on zebrafish reproduction has been devoted to maximizing egg production (Laale, 1977), and until now little has been known about the reproductive ecology of wild zebrafish. In the early stages of development, the ovaries act as gonads in zebrafish, and only at 5-7 weeks, with a length of 10-15 mm, male individuals begin to differentiate. However, the final intersecular period and the complete formation of the testes in males ends around the third month of postembryonic development (Devlin & Nagahama, 2002; Maak & Segner, 2003). The genetic mechanisms of sexual determination are unknown. However, there is evidence that the rate of differentiation is affected by food availability and growth rate. In this case, rapidly growing and large individuals become females, and small ones become males (Lawrence, Ebersole & Kesseli, 2007). Based on samples taken from the population in the Brahmaputra River, a natural sex ratio of 1:1 was found (Spence et al., 2007a). Under laboratory conditions, domestic breeds of zebrafish breed all year round, while natural breeds breed seasonally. However, large females caught in January (i.e., long before the start of the spawning period) had mature eggs, which indicates that the impact on reproduction is not so much the season as the availability of food (Spence et al., 2006a). In addition, the onset of puberty is related to size rather than age; wild and laboratory zebrafish matured being the same size, regardless of their growth rate. Eaton and Farley (1974a) showed that at 25.5°C domestic zebrafish rarely become sexually mature before 75 days, when females are 24.9 mm long and males 23.1 mm. Under laboratory conditions, the first generation of zebrafish is also ready to spawn at a length of approximately 23 mm. Pairs of zebrafish stay together and breed continuously, but spawning cycles are irregular (Eaton & Farley, 1974b). One female for spawning produces small packs containing several hundred eggs. Intervals between spawning vary from 1 to 6 days, with an average of 1.5 days. At the same time, packs of 1-700 eggs are laid (average value 185) (Spence & Smith, 2006). Pack size correlates with female size as well as spawning interval. This interval has been reported to increase with the maturation of the female, from 1.9 days for a 1-year-old to 2.7 days for a 15-month-old. In addition, the clutch size increased from 158 to 195, respectively (Eaton & Farley, 1974b). Ovulation depends on how much females are exposed to the male's gonodal pheromones. Males release testis homogenate and a gonadal fraction into the water containing steroidal glucuronides that induce ovulation. Interestingly, anosmic females cauterized with olfactory epithelium did not respond to pheromones (van den Hurk & Lambert, 1983; van den Hurk et al., 1987). Eaton & Farley (1974b). The presence of males for 7 hours in the evening is sufficient for females to start spawning the next morning (Eaton & Farley, 1974b). In isolated females that have been in contact with a male for a period of at least 5 days, spawning is never observed twice. This indicates that all mature eggs are shed in one spawning cycle (Hisaoka & Firlitt, 1962; Eaton & Farley, 1974b). The presence of a male is necessary for the maturation of eggs in females. In isolated or old females, eggs begin to stick together in aggregates, which often leads to their death. Examination of sick individuals showed the presence of rotting eggs stuck to the oviduct and preventing successful mating. Regular contact with the male and spawning excludes the development of necrotic foci. It is interesting that, despite the cyclicity and inconsistency of spawning, females that are in contact with the male a few days before breeding demonstrate better fecundity and egg quality compared to individuals isolated for several days (Gerlach, 2006). This effect is associated with the concentration of the presented pheromones. Both sexes have been shown to secrete pheromones that act as attractants before and during reproduction (Bloom & Perlmutter, 1977). At the same time, the sensitivity to their action is higher during spawning. Zebrafish eggs do not have a sticky shell and are dimersal (bottom). Their diameter is 0.7 mm. Spawning takes place directly over the substrate, which is not prepared in advance. Producers do not care about offspring. Both fertilized and unfertilized eggs are activated upon contact with water and undergo a series of programmed developmental stages. Unfertilized eggs develop into the periyolk space, but the process stops long before the first divisions (Lee, Webb & Miller, 1999). The incubation period at 28.5 °C varies from 48 to 72 hours, depending on the thickness of the chorion and the activity of the muscles of the embryo (Kimmel et al., 1995).

Immediately after hatching, the 3 mm long larvae are attached to the substrate by small secretory cells located on the head (Laale, 1977). Attachment at a higher level allows access to the surface needed to inflate the swim bladder (Goolish & Okutake 1999). This process is observed by 72 hours after fertilization, after which the juveniles switch to active swimming, feeding, and they develop avoidance behavior (Kimmel et al., 1995). Direct reproduction of zebrafish As you know, spawning of domestic zebrafish depends on the photoperiod (Breder & Rosen, 1966). Individuals exhibit a diurnal activity pattern synchronized with day/night and feeding cycles. The first peak of activity is observed immediately after the start of illumination, and the next two peaks are observed at the beginning of the evening and at the last hour of the daylight hours (Baganz et al., 2005; Plaut, 2000). Spawning is associated with the first peak, usually starts in the first minute after illumination after dark and lasts about an hour (Darrow & Harris, 2004). Field observations have shown that zebrafish breeding in nature is also, for the most part, limited to short periods at dawn (Spence, Ashton & Smith, 2007). However, compared with domesticated individuals, wild individuals have a more pronounced tendency to breed at other times than at dawn. The lengthening of daylight hours may be a factor that triggers reproduction in the natural habitat. The addition of cold water to the aquarium also encourages spawning in the aquarium (Breder & Rosen, 1966). Thus, a decrease in water temperature or an increase in its level serves as an additional signal for zebrafish. In nature, these fish spawn during periods of prolonged rains. Courtship during breeding consists of chasing the female by the male, touching her sides with his muzzle, swimming with spread fins around her in a figure eight or circles, and directing the female to the spawning area. If the female does not follow him, then the male continues to circle from her to the spawning site. Right above the selected substrate, the male swims close to the female, spreads the dorsal and caudal fins around her body so that the genital pores of the individuals approach each other, and the male himself could twitch with high frequency and low amplitude. This behavior triggers the simultaneous release of eggs and sperm. For one spawning, it is repeated several times, and at each stage, the female releases 5-20 eggs. Male courtship is most active in the first 30 minutes, although lasting about an hour, while the female spawns in the first half hour (Darrow & Harris, 2004). Wild zebrafish show similar territorial behavior and courtship behavior (Spence et al., 2007b). Under natural conditions, males are forced to pursue the female throughout the entire water column, while the female rises to the surface, and then sinks to the bottom to the spawning site. Usually 3-7 individuals are involved in the race. Courtship by the male is triggered by the pheromones of the females. Males, but not females, were attracted to egg extract added to an aquarium (Hurk & Lambert, 1983). Anosmic males (devoid of smell) showed no courtship, while controls courted only ovulating females. In addition, anosmic zebrafish were extremely aggressive, which indicates the inhibitory effect of pheromones on aggression, which is expressed in both sexes during feeding. Danios show a breeding pattern common to many cyprinids; they have group spawning and free scattering of eggs (Breder & Rosen, 1966). Females spawn directly on bare substrate, but if there is a good artificial substrate, such as a plastic surface, they prefer to lay their eggs on it (Spence & Smith, 2005). Some male zebrafish are territorial during spawning (Spence & Smith, 2005). Both territorial and common males display similar courtship behaviors. However, while non-territorial fish pursue females, territorial activity is limited to a few body lengths from the spawning site, from which they drive males away. Territorial aggression has been studied in a study of sex ratios and group density (Spence & Smith, 2005). It turned out that its degree increases depending on the planting density. Courtship behavior increases with the proportion of females, while in the male-dominated group, the degree of courtship decreased to the level observed at low stocking densities. The breeding success of territorial males has been shown to be dependent on stocking density (Spence, Jordan & Smith, 2006). At low densities, territorial individuals produced much more offspring than non-territorial ones. The reverse trend was observed with an increase in the size of the group. Thus, zebrafish males demonstrate two breeding tactics, guarding the site and actively chasing females, the success of which is related to the population size. High stocking densities result in reduced female egg production (Spence & Smith, 2005). This phenomenon is determined by a decrease in the number of eggs in packs released per spawning, rather than with the removal of part of the females from breeding (Spence et al. , 2006b). There are several explanations for this; an increase in male aggression towards each other can affect the competition of females and their access to spawning grounds. In addition, reduced egg production may be due to inhibition by pheromones emitted by other females. It has been shown that females that are under the influence of pheromones of other females prior to spawning are less willing to breed compared to isolated fish (Gerlach, 2006). It should be noted that dominant females produce more eggs (Gerlach, 2006). In studies using large 2*2 meter tanks, avoidance by females of each other and, moreover, exposure to each other's pheromones has been demonstrated (Delaney et al., 2002). Females prefer to be in groups consisting of one or more males than females. Thus, in reproduction, zebrafish plays a role as competition, both among males and among females.

Sexual partner preferences. The relationship between male and female zebrafish

Under natural conditions, it is difficult to determine the preferences of females in those species whose males compete for the opportunity to mate. In this case, the key role is played by the dominance of one or another male. However, there is evidence that females prefer larger males (Pyron, 2003). This is consistent with the data that the body size of bony fish correlates with their dominance in the group (Wootton, 1998). When looking at roe production as a measure of preference, females were found to have roe relative to certain males (Spence & Smith, 2006). However, no correlation was observed with either male dominance or possible female selection (Spence & Smith, 2006). There have been suggestions about the role of pheromones in the choice of a sexual partner. In particular, female zebrafish prefer the scents of foreign males to those of their brothers (Gerlach & Lysiak, 2006). It is possible that two mechanisms of sexual selection, male competition and female preference, simultaneously participate in reproduction. For example, if a female does not want to mate with a dominant male, then he can still do it to the best of his ability. In addition, competition among males for mating may be closely related to competition among females (Gerlach, 2006). In fact, breeding success is similar between male and female zebrafish, and sexual selection plays a minor role (Spence et al., 2006b). This is confirmed by their weak sexual dimorphism.

Substrate Selection The female prefers a specific substrate for spawning. Studies with domesticated and wild individuals in isolated cages found that females preferred gravel bottoms over muddy bottoms (Spence et al., 2007b). Territorial males also tend to protect benthic areas with gravel. This behavior is explained by the much better survival of eggs on a solid substrate, where they are supplied with oxygen and are also protected from cannibalism. Under laboratory conditions, preferences for plant thickets were also revealed, although the latter do not affect the safety of the masonry in any way. However, plants make a significant contribution to increasing the survival of larvae; they provide sites for attachment and help reach the surface for the inflation of the swim bladder (Laale, 1977). In natural areas where zebrafish are the dominant species, such as floodplain ponds, muddy ground is often present, and fish make their way to spawn in shallow water among vegetation that protects them from predators (Engeszer et al., 2007; Spence et al., 2007b) . Thus, the choice of producers is directed to places with better water circulation, where there are no predators. The search for spawning areas is one of the few mechanisms in species that do not show concern for offspring. It helps to increase the survival of masonry and larvae.

Danio fry

Danio fry need live starter food, but substitutes can be dispensed with if necessary. Let's look at the most important points in zebrafish rearing as a tip, when zebrafish fry grow in winter and do not receive live, complete food.
By the time the zebrafish fry swim, you need to be prepared in advance. Danio fry eat well its boiled yolk, and will have to be used as a starter feed. To raise several hundred fry, one chicken egg will be enough. Boil the egg and separate the yolk from it so that the yolk does not deteriorate, it must always be stored in the refrigerator.
Before feeding the fry, take a transparent glass or jar, fill it with water, then take the yolk, cut off the top from it and rub it over the surface of the cut part of the yolk with your index finger or watercolor brush, then rinse the brush or finger in the jar with water.
After the suspended particles of the yolk settle to the bottom, drain the cloudy water and repeat until the water becomes clear. Then, carefully and preferably, pour water with yolk to the fry into the aquarium on the compressor sprayer.

Be sure to plant snails in the aquarium, these snails, eating uneaten yolk particles, are of great benefit, keeping the aquarium clean. After 7-10 days, when the fry grow up, they need to be transferred to a larger feed. A good transition would be to scraped beef heart.
It is very important to monitor the water temperature. An increase in water temperature increases metabolism, in the body of fish, the growth of fry accelerates, but there is a chapel for everything, to cross which means to destroy the fish.
Danio fry grow well at a water temperature of 26 ° C; it is not recommended to raise the water temperature above. As the zebrafish fry grow, the water temperature must be gradually lowered.

Danio fry eventually turn into such beautiful, in this case, pink large zebrafish.

Good luck with danio!