The habitats of the fish were determined by their appearance. External structure of fish: description, features. Shallow water zone, or continental shelf

It is impossible to describe all the countless habitats of fish, ranging from small streams and ponds to vast oceans. Therefore, we are forced to limit ourselves to three main types of fish ecosystems: lakes, rivers and seas. In addition, there are many intermediate fish habitats that we do not stop at. Our main focus now is on geographic zones with temperate climates.

Lakes

Lakes can be classified different ways. Here we rely on their ability to reproduce organic matter. Oligotrophic lakes are nutrient-poor, relatively deep, and contain few living organisms. Eutrophic lakes, rich in nutrients and quite shallow, are the source of rich organic life.

The productivity of a lake is determined primarily by its basin, that is, the place of drainage or precipitation collection, as well as climate. As a rule, most oligotrophic lakes are located in areas with insignificant ancient rock deposits, and the majority of eutrophic lakes are located in regions rich in limestone. Lakes in densely populated parts of the Western world are becoming increasingly eutrophic, constantly receiving nutrients from municipal and farm runoff. This ever-increasing influx of nutrients, as we will soon see, poses a serious threat to salmonids, although at present such conditions suit so-called eutrophic species, mainly the numerous cyprionids.

Life in the lake

The life of animals and vegetation in the lake largely depends on the availability of food in it. Both the number and diversity of living organisms differ significantly in eutrophic and oligotrophic lakes. However, both of these types of lakes have common biotic features.

Plankton - This is a large group of tiny organisms floating in water, whose movement is more or less dependent on the current. This applies to a greater extent to plant species (phytoplankton), while animal species (zooplankton) are more active swimmers. The bulk of zooplankton lives in the free waters of the lake, which are called the pelagic zone. Some of them, such as copepods and cladocerans, perform vertical diurnal migrations, rising to the surface of the water at night and returning to the depths during the day. This migration phenomenon has not yet been explained, but is probably related to sunlight. As we will see, plankton is the main food for almost all juvenile fish, as well as for many species of adult fish.

Nekton usually involves swimming organisms, particularly the strongest of them, which can change the direction of their swimming at will. Mainly, of course, these are fish, as well as some other organisms, such as crustaceans and waterfowl, which are also classified as nekton.

Benthos - This is a group of organisms that live or rest on the bottom. They live in bottom sediments or are connected to the bottom by some other conditions of their life or nutrition. In the coastal zone of lakes, the environment is very diverse, intense and requires special adaptation. For example, species living on areas of steep, wind-exposed, rocky bottoms must be able to withstand mechanical pressure. Like many river animals, they often have quite flat body, and sometimes claws, suckers or rough pads on the limbs. In contrast, individuals living in a calm lagoon with a clay or muddy bottom can be quite fragile. They only need to inhale enough oxygen to compensate for the lack of it that often occurs in such places. Thanks to photosynthesis, such protected environments are usually highly productive in terms of vegetation. Its benthos is often very diverse and includes worms, mollusks, crustaceans and insects at various stages of development.

The coastal zone of the lake is richest in species diversity. As you move deeper, the number of species decreases due to greater depletion of habitat.

In a eutrophic lake, benthos consists mainly of root vegetation in the coastal zone. The shallows of this zone are inhabited by heliophytes - light-loving vegetation with long stems, with their upper parts directed towards the surface. Next to them there are rooted plants with floating leaves, whose flowers barely reach the surface of the water. Next are the bottom root plants, completely hidden under water. This deep-sea vegetation is usually not characteristic of eutrophic lakes, but is of great importance for oligotrophic reservoirs.

Food chains in the lake

The main food producers in lakes are green algae. Using their chlorophyll, they produce nutrients through photosynthesis from solar energy, carbon dioxide and water. In a certain sense, they feed themselves, but still depend on external feeding. Among other things, they need bacteria to decompose dead matter and thus provide them with basic food supplies. Therefore, bacteria should be considered as the basis of the food web in lakes.

Green algae represent the first cell of this network. They are followed by herbivores - the main consumers who have to choose between living and dead plant materials. We hardly know what they prefer. Herbivorous organisms living at depths where there is not enough sunlight to grow green algae must naturally feed on dead matter that falls there from the surface. They may also constitute the main diet of herbivores in the coastal zone.

Food chains in a temperate lake climate zone. These chains do not necessarily lead from primary consumers to final consumers. Due to their close interconnections, they often form complex food chain in their environment.

A detritus
b mayfly larvae
With coastal algae
d phytoplankton
e coastal plants
f shellfish
g rotifers
h cyclops
i Daphnia
j water donkey
k bloodworm
l freshwater snails
m horseleech
n mayfly
O perch fry
R trout
q perch
r pike

The third cell of the food web consists of carnivores that eat herbivores. Other animals feed on them, mainly fish, which represent the fourth cell, etc. Any simple sequence of organisms within this network is already a food chain, but the diet of most organisms covers several food chains, which are intertwined in a complex way, sometimes into a very intricate food web. This pattern can also change over time: for example, when young, most fish feed on zooplankton, then switch to bottom dwellers, and some, like carp, can feed on algae as adults.

Where do the fish live in the lake?

Fish occupy almost all habitat niches, or biotopes, of the lake, but the main number of species and individuals are located in the coastal zone. Naturally, plankton-eating fish such as whitefish, which live mainly in pelagic waters, are much less attached to the coastal zone than, for example, trout, whose main source of food is located there.

The picture shows a “fictional” lake, on which the most likely habitats of fish are marked: (a) the confluence of a stream, river, (b) a swampy shore, (c) a cape, (d) the source of a stream, river, (e) overhanging trees, (f) boulders at the bottom.

As in the sea, the habitat of fish in a lake is determined by many factors. Water temperature is often of great importance. This forces fish such as pike, which are relatively well adapted to cold water, remain in shallow waters in the spring and fall, but move to cooler, deeper waters in the summer. They say that perch loves warmth and stays in the warmest places or layers of water in all seasons, even if the temperature difference is only a few tenths of a degree.

It is stated that trout live mainly in the coastal zone, and we are likely to find them there at any time of the year, unless, of course, our definition of this zone is too narrow.

Flowing reservoirs

Depending on the size and volume, water flows are divided into streams, rivers and rivers. In terms of speed of water flow, they are classified into backwaters, rapids, waterfalls, etc. A backwater is an area of ​​more or less standing water between streams or fast streams. We also distinguish upstream stream or waterfall, meaning its beginning, and the bottom
flow - end.

The area from which water flows into a river is called catchment area. Watershed - these are the elevations separating different catchment areas. The volume of water flowing per unit time through any section of a waterway is known as water consumption. It is usually measured in cubic meters (thousands of liters) per second. Water flow per unit of catchment area is called river flow, usually measured in liters per second per square kilometer. Water level - this is the height of the water surface in relation to a specific mark and is measured with a special instrument with a centimeter scale.

Life in the water stream

As mentioned above, in lakes the role of the primary producer belongs to plankton. However, the water flow does not create the most favorable conditions for the existence of these drifting organisms. The plankton found here is usually carried by water from lakes or slow-moving (standing) bodies of water.

In fast-flowing water streams, green vegetation mainly consists of mosses, lichens and algae covering the rocks at the bottom. Only in calm areas of streams or rivers can you find more developed aquatic plants that influence primary reproduction.

Despite this, the process may be even more intense than in any other known ecosystem. The reason for this phenomenon lies in the fact that the flow of water constantly brings the substances necessary for these organisms and carries away their decay products. This efficient exchange allows these organisms to produce much more than would otherwise be expected.

At the same time, water flow creates extreme and stressful conditions to which various organisms often have to adapt. The flattened bodies and claws that allow insect larvae to cling to the rough surface of stones are of much greater importance here than in their counterparts living along the shores of lakes. Many river insect larvae, such as stoneflies, have flattened bodies, although it is not known whether this is due to adaptation to water pressure or the need to hide in cracks to escape the flow of water.

Temperate rivers originate high in the mountains and flow into the seas, where fresh water mixes with salt water. (1) The cold and oxygenated water of the source flows down often along a rather rocky bed. Animals have adapted to these conditions: they swim well, like salmon and trout, skillfully use areas of calm water, like a goby, etc. (2) Downstream, the depth increases and the strength of the flow weakens, there is still enough oxygen in the water, and rocky The bottom is covered in some places with sand and gravel.
(3) In the lower half of the river the bottom is mostly sand and gravel and the flow is much slower. Perch and eel are often found here. (4) In its lower course, the river rather resembles a pond, where muddy water flows slowly along the muddy bottom. There is a wide variety of plant and animal life all around. Most fish move slowly and have high profile bodies, such as carp and the most famous predator - pike.

Other adaptive changes in animals that are at risk of being swept away by fast currents include a reduction in the size of protruding body parts, such as in mayfly larvae. Some types of articulated animals are held in place by secretions secreted by salivary glands. The danger of being washed away by water can also be reduced by using weight or load - for example, some larvae make “houses” for themselves out of sand and pieces of gravel. Fish also adapt to the strong pressure of the water flow, so species living in rapids usually have the most streamlined body shapes.

Organic demolition

The drift of living and dead organic materials in a stream of water is known as organic drift. It is a mixture of insects and their larvae that have fallen to the surface of the water, plankton washed away from lakes, organisms carried away from the bottom, etc. These organic substances are partially consumed by a certain type of organisms called filterers. They obtain food from drifting fauna, using various catching devices for this. Quite simple in some species, in others they can be quite complex, for example, networks with such small cells that they can even trap bacteria! The greatest drift of organic matter usually occurs from lakes and other bodies of water with slow-moving water. There are also the maximum number of filter feeders and, accordingly, more crustacean predators that feed on them. Thus, drift, filter feeders and predators “work together” to form a food chain as efficient as a factory. The particles of nutrients contained in the water, as a rule, are too small to interest the fish, are retained by filter feeders, and when they come off the bottom, they accumulate in predators.

On the diagram of the river section and its sections with different course The places where fish usually gather are marked: (a) deep pool, (b) weak surface current, (c) calm surface area, (d) fast bottom current, (e) shallow with a fast current, (f) beginning of a stream with a calm current.

Since this process occurs mainly at the outlets of lakes, these areas of water flows are very productive and are popular with fish and, naturally, anglers. In fact, many river fish use this drift as well as filter feeders. Instead of chasing prey, they choose a strategically advantageous place in the stream and grab everything that floats past. This behavior in the water flow is characteristic, for example, of young salmon, river and rainbow trout, as well as, to some extent, grayling and char.

Fish habitats in water streams

Most species of freshwater fish can be found in water streams. Many of them live in both lakes and rivers. Moreover, all these fish live in their own specific territory.

Some fish that live in fast (flowing) streams are anatomically adapted to them. As a rule, they have a fairly streamlined body. Salmonids, such as trout and grayling, are adapted to fast current in many respects, although grayling usually prefers quieter places than trout, which resemble salmon in its habits. Other species, for example, gobies and catfish, stick to the bottom and seek refuge behind or under rocks. Carp and pike usually live in calmer areas of rivers and streams.

The habitats of fish in running water are not determined by any strict rules, since the species themselves and their ability to adapt create a lot of variation. Possible trout habitats in sections of the river with different flow rates are shown below.

Food chains in the sea resemble similar connections in continental lakes, but are more dependent on plant photosynthesis. Here, numerous food chains also intertwine and form a complex food pyramid. Zooplankton is of great importance for nutrition.

A detritus
b brown seaweed
With phytoplankton
d mussels
e scallop
f bivalves
g sea ​​snails
h- P zooplankton
O crabs
R sea ​​stars
q flounder
r shrimp
s herring
t bulls
And cod
v shark

Sea

Thanks to the vast area of ​​the world's oceans and its average depth, which is approximately 3800 meters, marine organisms have a much larger living space than their continental counterparts, which are usually limited to their habitat. Yet the marine fauna is comparatively poor in species: the seas are home to about 160,000 of the million known animal species on earth, two-thirds of which are insects that you won’t find in the sea.

Like lakes, seas have different zones.
Pelagic zone open water space is practically divided into two zones, or regions. Neritic(coastal) zone, including the waters of the continental shelf to depths of approximately 200 meters, beyond which the oceanic the zone, roughly speaking, corresponds to the coastal zone of lakes. Greatest variety environment characteristic specifically of the neritic zone with its shores, areas overgrown with seaweed, estuaries, shallows and coral reefs of the southern seas, etc., as well as numerous species and varieties of fish.

Life of the sea

Animals and plants found exclusively in the pelagic zone - among them approximately 200 species of animals and almost all microscopic algae - are classified by biologists as holopelagic species Organisms that live primarily in the pelagic zone but spend some stages of their lives on the bottom of the benthic zones are called meropelagine. This group includes about 1,000 species of animals, such as jellyfish.

Between meropelagic animals and real ones benthic species have many transitional forms. For example, adult herring live in pelagic conditions, but the eggs they lay mature on the bottom. Cod lay their eggs in pelagic waters but lead a benthic life. Even flounder and other flat fish initially develop in the pelagic zone. This is practically where most benthic marine animals go through the embryonic stage of their development.

Marine organisms, like lake organisms, are divided into plankton and nekton. Almost all primary reproduction in the sea depends on phytoplankton (algae). The most important type phytoplankton, in addition to diatoms, are flagellates. They also live in lakes and provide one of the main types of microscopic food for crustaceans, which, in turn, feed on herring. Flagellates are famous for appearing in huge numbers, especially in tropical seas, where their brown-red shells color large areas of the water and form the so-called “red current”.

The main marine zooplankton are crustaceans such as copepods Calanus finmarchicus. It is probably the main type of animal food on earth, living in almost all oceans, from their surface to depths of 3000 meters. In addition, this krill is an unsurpassed filter feeder of microscopic algae, and is therefore of paramount importance as a source of nutrition in the sea. Marine nekton consists of fish, cephalopods (squid, octopus, cuttlefish), mammals and birds.

The various habitats of marine animals along this coastline have been created by the movement of wind and water. Among them, three main types can be distinguished. (1) Consisting of rocks, large stones and gravel Rocky coast, which is hit by waves. It provides different habitat niches for plants, fish and other animals, depending on the depth.

(2) On shallow beaches subject to the constant influence of tides, animal life must be adapted to the harsh conditions associated with long dry periods or winds blowing from land.

(3) Further afield, near the mouth of the river, the environment is more sheltered and the beaches are often covered with sand or clay with some rocks interspersed.

While the number of pelagic species of marine animals is only about 3000, benthic species number approximately
150,000. They live mainly in coastal areas at depths of up to 200 meters. The diversity of life forms in the seas of the Arctic and Antarctic is much poorer than in tropical seas. This distribution of species is largely determined by temperature, which in turn depends on geographical latitude and large ocean currents.

Fish habitats in the sea

Marine organisms appear to have an unlimited ability to adapt to their environment. Fish are found at almost all depths, although the number of their species and individuals is much greater in coastal waters. This zone provides them with a wide range of environments from coastal areas, seagrass beds and estuaries to offshore shallows. Specific habitats sea ​​fish depend, in particular, on the depth, salinity of water, current and structure of the bottom (substrate). The most striking examples This is the flounder, whose body has adapted to the bottom lifestyle, or mackerel and tuna, whose torpedo-shaped bodies allow them to develop high speed and dive to great depths. In general, the habitats of marine animals in the coastal zone can be divided into coastal waters and waters surrounding islands and reefs in the open sea. A typical example of the first option is shown in the accompanying illustration.

Fish are one of the most amazing aquatic animals. What features allowed them to adapt to life in these conditions? From our article you will learn about the external structure of fish and their diversity.

Habitat

It’s not for nothing that they say about confident people: “They feel like a fish in water.” These animals are not able to absorb oxygen from the air. Therefore, this environment is comfortable for them. The only exception is a small group of lungfish. They have both gills and lungs. The latter allow them to survive unfavorable periods of drying out water bodies and lack of oxygen.

Fish live in fresh and salt water. It depends on their type. Thus, gobies feel great even with an increase in salt concentration of 60%, and the carp dies.

Fish are also adapted to different temperatures. This indicator is also individual. Californian lucania prefers to live in water with a temperature of + 50. And dalia, which lives in small streams in Chukotka, freezes and thaws along with the water.

Features of the external structure of fish

Cartilaginous fish lack gill covers and swim bladders. The respiratory organs open outwards with independent openings. The skeleton of cartilaginous fish does not ossify. Ducts of the reproductive, digestive and excretory system open into one hole - the cloaca.

Sharks

The mere mention of these fish becomes scary. Indeed, most sharks lead a predatory lifestyle. Although the whale and basking sharks, which are the largest representatives of the class, are quite harmless. The basis of their diet is planktonic organisms.

The body of sharks has a streamlined shape. Special meaning It has a caudal fin for movement. In most species it is variegated. It is also called heterocercal. In this case, the upper blade is much larger than the lower one.

There is a mouth on the elongated crescent-shaped head. It is surrounded by a large number of teeth arranged in several rows. As some of them wear off, others grow from the inside.

Is it true that sharks are fish without scales? It's not like that at all. Although at first glance her skin seems completely bare. Shark scales are called placoid scales. It is the most ancient in origin. In composition, shape and chemical structure, placoid scales resemble teeth. This is a plate with a spike protruding outward. Shark scales have a wide base and a flattened shape. The plates fit so tightly to each other that the skin appears bare. In fact, it protects the body of sharks like iron chain mail.

Placoid scales also perform additional functions. It significantly reduces water resistance, which allows sharks to reach speeds of up to 80 km/h. It also allows for virtually silent movements. This is very important during hunting and attack.

Stingrays

These fish have both a tail and scales. But their appearance is very unusual. Their body is flattened in the dorso-ventral direction. The pectoral fins of fish are fused to the head, resembling wings. We're talking about stingrays.

Most of them live in the seas, but inhabitants of fresh water bodies are also known. Depending on their habitat, the color of stingrays varies from yellowish to black. The eyes are located on the upper side of the body. There are also sprinklers here. They represent the first pair of gill slits, which open the arches of the respiratory organs.

The characteristic body shape is interconnected with their bottom-dwelling lifestyle. Stingrays swim due to the wave-like movements of their wide pectoral fins. But they spend most of their time at the bottom. Here they bury themselves in the sand or wait for prey. The diet of these fish consists of small invertebrates, fish or plankton.

Bony fish

This class is much more numerous. Its representatives are more than 20 thousand species. They live in all types of reservoirs: from small rivers to ocean expanses.

These fish have more progressive structural features. These include the presence of a fully ossified skeleton and a swim bladder, which holds the body in the water column. The respiratory organs of bony fishes are protected by gill covers. The latter not only protect them, but also take part in the implementation of respiratory movements.

Fish without scales: is it possible?

The skin of fish contains numerous glands. They perform a protective function. The substances they secrete prevent the penetration of pathogenic microorganisms and reduce water friction during swimming. In some species, mucus contains toxic substances.

The body of bony fishes is also covered with scales, which are derivatives of the skin. It looks like translucent flat plates. The individual scales overlap each other like tiles. With its front edge, each plate goes deep into the skin, and the back one covers the scales of the next row. The growth of these structures is similar to the formation of tree rings. The growth of the plates occurs in the spring and stops in the winter.

Do all fish have scales? Absolutely. But in some it completely covers the body, while in others it is located on the body in separate rows. The latter traditionally includes cartilaginous fish and some bony fish. For example, beluga, sterlet, sturgeon and stellate sturgeon have sharp scales located along the body in several strands.

Features of covers

All features of the external structure of fish allow them to better adapt to life in the aquatic environment. Not only the speed of movement, but also the color of the integument allows them to hide from predators. In many fish it is protective. For example, the dorsal side of the perch is darker than the ventral side. This makes the fish less noticeable against the bottom. The belly of the perch is silver. This makes it invisible against the background of the water surface for prey, which is located below. Transverse stripes provide perch with excellent camouflage among algae thickets.

Other species have variegated and bright colors. It is called warning because its owners are almost always poisonous. Flounder has the ability to change its color depending on environmental conditions.

What is the lateral line in fish?

A thin stripe is clearly visible to the naked eye on both sides of the body. It stretches from the gill slits to the base of the tail. This structure is called the lateral line. It consists of receptors called neuromasts. The latter are formed by a group of hair cells.

The lateral line in fish is the organ for sensing vibrations and movements in the environment. With its help, fish determine the direction and speed of the current. A similar structure is found in all larvae and some adult species of amphibians, cephalopods and crustaceans. Fish use it as a landmark in space, which is especially important during hunting.

Unusual species

Despite a large number of general structural features, there are a number of aquatic inhabitants that are in no way similar to representatives of this class. One of them is the blob fish. For most of her life, she has a normal appearance: tail, scales, fins... However, when she rises to the surface of the water, her body begins to swell and turn into a gelatinous creature, similar to a monster with a huge nose.

In the coral ocean reefs you can find body fish. It has the shape of a cube. You can add bright yellow with black dots to this unusual look. So far, scientists cannot explain why, during the process of evolutionary changes, the classic flat shape of the body changed to a cubic one.

Flat head with a vermiform appendage on which the eyes are located blue color, a huge mouth, bright stripes on the skin... Such an organism really exists. It's called frog fish. It was discovered in Indonesian waters not so long ago - in 2009.

And how can we not talk about the stargazer fish! You definitely won't confuse her with anyone. The Stargazer can be recognized by its two bulging eyes and wide mouth, which is located on top of its head. He burrows into the sand, tracking his prey. At first glance, this is an absolutely harmless fish. In fact, its spines, located above its dorsal fins, contain poisonous substances and are capable of generating small amounts of electrical current.

So, the features of the external structure of fish that help them adapt to life in water include:

• Streamlined body shape. It consists of a head, body and tail. In benthic species that lead a sedentary lifestyle, the body is flattened in the dorsoventral direction.
• A large number of glands that secrete mucus.
• Scales that cover the body of a fish completely or form longitudinal stripes.
• In cartilaginous fish, the respiratory organs open outward through gill slits. In bones, they are closed with covers that protect the respiratory organs and are involved in respiratory movements.
• The presence of several types of fins: paired and unpaired. The first group includes abdominal and thoracic. The dorsal, caudal and anal are unpaired. They provide all types of movements, maneuverability and stable position in the water column.

The littoral zone is a place where there are almost no fish, since it is not yet a “full-fledged” body of water, but the border between the coast and the tidal zone. Therefore, only some fish risk entering the littoral zone. These include, in particular, mudskipper, which stores water behind its cheeks and can get out even further than the littoral zone, climbing trees and intertwined roots. During high tide, jumpers often sit on tree branches, clinging tightly to them with their fused ventral fins. There are 10-12 species of these fish, which have a head resembling that of a hippopotamus, with bulging frog eyes.

They travel overland in search of earthworms and other living creatures - slider fish, oblong, reaching 15 cm in length. California gillicht gobies live without water in a damp, cool place for several days. Eels can crawl on the ground and outside the littoral zone, moving to other bodies of water if necessary. Some fish, for example, sphinx blennies, can sit in the littoral zone for a short time when thrown out by the tide, waiting new wave. Protoptera, lepidosirene and cattail, can live for some time without water in the littoral zone due to the presence of special lungs. Some polyfins can crawl out to the littoral zone and “travel” along it. Juvenile flag-tailed shorebirds prefer to stay in the pools formed by the tide. Only at the border of the littoral zone and the continental shelf is there constant water; there are small fish such as blennies, small catfish, greenfinches, needle fish, some coral fish, as well as lungfish and some cartilaginous ganoid fish.

Shallow water zone, or continental shelf

Shallow water area, or continental shelf- habitat of important commercial fish: sturgeon, sprat, anchovy and many others. Herring, mackerel, tuna and other fish often come here during times of abundance of food. Among small fish of temperate waters, the first place in terms of total mass is occupied by anchovies, followed by predators: cod, sharks. In this zone, young fish of many species live their childhood. Grunion silverside fish, living in schools in the shallow waters of Mexico and California, breed in the littoral zone, burying their eggs in the sand at the water's edge during high tides. At low tide, the eggs develop in the warm, wet sand. In other species of silverside eggs, the eggs have thread-like appendages with which they are attached to some substrate.

They are found among fish of the continental shelf and sucker fish, in which fused pelvic fins form a suction cup, allowing them to cling to coastal stones even during strong waves. Many fish that have no particular commercial value also live on the continental shelf: blennies, greenfinches, and cockerels.

In Australia, dangerous fish also live in the continental shelf zone: for example, sand and great white shark. In other places in shallow waters there are sharks: hammerhead shark, herring shark, blue shark, but there are also safe types, like leopard and cat sharks.

Coral Reefs: A Zone of Super-Rich Seas

Coral reefs are an area where all the brightest, strangest and funniest fish are gathered in one heap. Only on one Big barrier reef you can find one and a half thousand species of fish of the most diverse shapes and colors, from clownfish to ragpickers.

Formed Coral reefs many millions of years in small areas warm waters near the Antilles and Sunda Islands, not far from Australia, Africa, Madagascar, Sri Lanka. Tiny skeletons of coral polyps gradually layered on top of each other to form coral islands.

The reef zone is home to many planktivores and herbivorous fish, which attract many predators, and among them a large proportion are cartilaginous fish.

The entire community of animals and plants of coral reefs is divided into several environmental groups. Thus, parrot fish, whose teeth are very similar to an arched beak, which is extremely convenient for biting off pieces of coral and algae, are destructors, that is, destroyers of corals. Among other destructors it is widely known Starfish"crown of thorns"

Let's now talk about the simplest of all types of relationships between fish - predator-prey relationships. There are a lot of predators here on the reefs! This is especially true for sharks. The most common are the so-called reef sharks. There are sand sharks, white sharks, spiny sharks, and herring sharks. There is even a carpet shark, which, like scorpionfish and monkfish, flat and disguised by growths! "Sea Shadows" are always ready to grab a wounded or unwary fish. Stingrays include stingrays, a variety of electric rays and sawfish. But next to these dangerous fish swim their harmless relatives - manta rays (as discussed in Chapter 3, they can only harm a person if they accidentally fly into a boat).

There are also bony predators. These include barracudas, moray eels, scorpionfish, anglerfish, and groupers - there is no room to list them! They can send most of their “neighbors” on the reef to a better world - except for the larger fish.

I did not talk separately about the fauna of the bottom zone, since it is similar in fauna to the reef zone. However, there are also some interesting fish. For example, a common bug from the order Percopsidae. A curious way is how it buries itself in the sand: swimming head first near the bottom, it abruptly goes into reverse and, sticking its tail into the sand, quickly sinks completely into it, working with its fins. There are also many unusual species eels.

Of the 40-41 thousand species of vertebrate animals existing on earth, fish are the richest group in species: v it has over 20 thousand living representatives. Such a multitude of species is explained, first of all, by the fact that fish are one of the oldest animals on earth - they appeared 400 million years ago, that is, when there were no birds, amphibians, or mammals on the globe. . During this period, fish have adapted to live in a wide variety of conditions: they live in the World Ocean, at depths of up to 10,000 m, and in high-mountain lakes, at an altitude of up to 6,000 m; some of them can live in mountain rivers, where water speed reaches 2 m/ s, and others - in standing reservoirs.

Of the 20 thousand species of fish, 11.6 thousand are marine, 8.3 thousand are freshwater, and the rest are anadromous. All fish belonging to a number of fish, based on their similarity and relationship, are divided according to the scheme developed by the Soviet academician L. S. Berg into two classes: cartilaginous and bony. Each class consists of subclasses, subclasses of superorders, superorders of orders, orders of families, families of genera, and genera of species.

Each species has characteristics that reflect its adaptability to certain conditions. All individuals of a species can interbreed and produce offspring. Each species in the process of development has adapted to known conditions of reproduction and nutrition, temperature and gas regimes and other factors of the aquatic environment.

The body shape is very diverse, which is caused by the adaptation of fish to various, sometimes very peculiar, conditions of the aquatic environment (Fig. 1.). The most common shapes are: torpedo-shaped, arrow-shaped, ribbon-shaped, acne-shaped, flat and spherical.

The body of the fish is covered with skin, which has upper layer- epidermis and lower - corium. The epidermis consists of a large number of epithelial cells; This layer contains mucus-secreting, pigment, luminous and poison-secreting glands. The corium, or skin itself, is a connective tissue penetrated by blood vessels and nerves. There are also clusters of large pigment cells and guanine crystals, which give the skin of fish a silvery color.

Most fish have a body covered with scales. It is not found in fish that swim at low speeds. The scales provide a smooth surface of the body and prevent skin folds on the sides.

Freshwater fish have bony scales. Based on the nature of the surface, two types of bone scales are distinguished: cycloid with a smooth posterior edge (cyprinid, herring) and ctenoid, the posterior edge of which is armed with spines (perch). Age is determined by the annual rings of bone scales bony fish(Fig. 2).

The age of a fish is also determined by the bones (bones operculum, jaw bone, large integumentary bone of the shoulder girdle-cleistrum, sections of hard and soft rays of fins, etc.) and otoliths (calcareous formations in the ear capsule), where, as on scales, layers are formed corresponding to the annual life cycles.

The sturgeon's body is covered special kind scales are bugs; they are located on the body in longitudinal rows and have a conical shape.

The skeleton of fish can be cartilaginous (sturgeon and lampreys) and bony (all other fish).

Fish fins are: paired - pectoral, ventral and unpaired - dorsal, anal, caudal. The dorsal fin can be one (in cyprinids), two (in perch) and three (in cod). The adipose fin, without bony rays, is a soft skin growth on the back of the back (in salmonids). The fins ensure the balance of the fish's body and its movement in different directions. The caudal fin creates driving force and acts as a rudder, providing maneuverability of the fish when turning. The dorsal and anal fins maintain the normal position of the fish's body, i.e., they act as a keel. The paired fins maintain balance and act as rudders for turns and depth (Fig. 3).

The respiratory organ is the gills, which are located on both sides of the head and covered with covers. When breathing, the fish swallows water with its mouth and pushes it out through the gills. Blood from the heart enters the gills, enriched with oxygen, and is distributed throughout the circulatory system. Carp, crucian carp, catfish, eel, loach and other fish that inhabit lake bodies of water, where there is often a lack of oxygen, are able to breathe through the skin. In some fish, the swim bladder, intestines and special accessory organs are capable of using oxygen atmospheric air. Thus, a snakehead, basking in shallow water, can breathe air through the epibranchial organ. The circulatory system of fish consists of the heart and blood vessels. Their heart is two-chambered (has only an atrium and a ventricle), and directs venous blood through the abdominal aorta to the gills. The most powerful blood vessels run along the spine. Fish have only one circulation. The digestive organs of fish are the mouth, pharynx, esophagus, stomach, liver, intestines, ending in the anus.

The shape of the mouth of fish is varied. Fish that feed on plankton have an upper mouth, bottom feeders have a lower mouth, predatory fish- terminal mouth. Many fish have teeth. Cyprinid fish have pharyngeal teeth. Behind the mouth of fish there is an oral cavity, where food initially enters, then it is sent to the pharynx, esophagus, stomach, where it begins to be digested under the influence of gastric juice. Partially digested food enters the small intestine, where the ducts of the pancreas and liver empty. The latter secretes bile, which accumulates in the gallbladder. Carp fish do not have a stomach, and food is digested in the intestines. Undigested food remains are excreted into the hind intestine and removed through the anus.

The excretory system of fish serves to remove metabolic products and ensure the water-salt composition of the body. The main excretory organs in fish are paired trunk kidneys with their excretory ducts - ureters, through which urine enters the bladder. To some extent, the skin, gills and intestines take part in excretion (removal of metabolic end products from the body).

The nervous system is divided into the central nervous system, which includes the brain and spinal cord, and the peripheral nervous system, which includes the nerves that extend from the brain and spinal cord. Nerve fibers extend from the brain, the endings of which reach the surface of the skin and form, in most fish, a pronounced lateral line running from the head to the beginning of the rays of the caudal fin. The lateral line serves to orient the fish: determining the strength and direction of the current, the presence of underwater objects, etc.

The organs of vision - two eyes - are located on the sides of the head. The lens is round, does not change shape and almost touches the flat cornea, so fish are myopic: most of them can distinguish objects at a distance of up to 1 m, and see a maximum of 1 at no more than 10-15 m.

The nostrils are located in front of each eye and lead into the blind olfactory sac.

The hearing organ of fish is also an organ of balance; it is located in the back of the skull, a cartilaginous or bone chamber: it consists of upper and lower sacs in which otoliths are located - pebbles consisting of calcium compounds.

Taste organs in the form of microscopic taste cells are located in the lining of the oral cavity and on the entire surface of the body. Fish have a well-developed sense of touch.

The reproductive organs in females are the ovaries (ovaries), in males - the testes (milts). Inside the ovary there are eggs, which in various fish have different sizes and color. The roe of most fish is edible and highly valuable. food product. The caviar of sturgeon and salmon fish has the highest nutritional quality.

The hydrostatic organ that ensures the buoyancy of fish is the swim bladder, filled with a mixture of gases and located above the insides. Some bottom-dwelling fish do not have a swim bladder.

The temperature sense of fish is associated with receptors located in the skin. The simplest reaction of fish to changes in water temperature is to move to places where the temperature is more favorable for them. Fish do not have thermoregulation mechanisms; their body temperature is not constant and corresponds to the water temperature or differs very slightly from it.

Fish and the external environment

Not only do they live in water different kinds fish, not only different types of fish, but also thousands of living creatures, plants and microscopic organisms. The bodies of water where fish live differ from each other. physical and chemical properties. All these factors influence the biological processes occurring in water and, consequently, the life of fish.

The relationship of fish with the external environment is combined into two groups of factors: abiotic and biotic.

Biotic factors include the world of animal and plant organisms that surround fish in water and act on it. This also includes intraspecific and interspecific relationships of fish.

Physical and Chemical properties water (temperature, salinity, gas content, etc.) acting on fish are called abiotic factors. Abiotic factors also include the size of the reservoir and its depth.

Without knowledge and study of these factors, it is impossible to successfully engage in fish farming.

An anthropogenic factor is the impact of human economic activity on a reservoir. Reclamation helps to increase the productivity of reservoirs, while pollution and water withdrawal reduce their productivity or turn them into dead reservoirs.

Abiotic factors of water bodies

The aquatic environment where fish live has certain physical and chemical properties, changes in which affect biological processes, occurring in water, and, consequently, on the life of fish and other living organisms and plants.

Water temperature. Different types of fish live at different temperatures. Thus, in the mountains of California, the lucan fish lives in warm springs at a water temperature of +50 ° C and above, and crucian carp spends the winter hibernating at the bottom of a frozen reservoir.

Water temperature is an important factor for the life of fish. It affects the timing of spawning, egg development, growth rate, gas exchange, and digestion.

Oxygen consumption is directly dependent on water temperature: when it decreases, oxygen consumption decreases, and when it increases, it increases. Water temperature also affects fish nutrition. When it increases, the speed of food digestion in fish increases, and vice versa. Thus, carp feeds most intensively at a water temperature of +23...+29°C, and at +15...+17°C it reduces its feeding by three to four times. Therefore, in pond farms the water temperature is constantly monitored. In fish farming, pools are widely used under thermal and nuclear power plants, underground thermal waters, warm sea ​​currents and etc.

The fish of our reservoirs and seas are divided into heat-loving (carp, sturgeon, catfish, eels) and cold-loving (cod and salmon). The water bodies of Kazakhstan are mainly inhabited by heat-loving fish, with the exception of new fish being bred, such as trout and whitefish, which are classified as cold-loving fish. Certain species - crucian carp, pike, roach, marinka and others - can withstand water temperature fluctuations from 20 to 25°C.

Heat-loving fish (carp, bream, roach, catfish, etc.) in winter concentrate in areas of the deep zone specific for each species; they show passivity, their feeding slows down or completely stops.

Pisces that lead active image life and in winter (salmon, whitefish, pike perch, etc.) are cold-loving.

The distribution of commercial fish in large bodies of water usually depends on the temperature in different areas of that body of water. It is used for fishing and commercial exploration.

Salinity of water also affects fish, although most of them can withstand its vibrations. The salinity of water is determined in parts per thousand: 1 ppm is equal to 1 g of dissolved salts in 1 liter of sea water, and it is denoted by the sign ‰. Certain types of fish can withstand water salinity up to 70‰, i.e. 70 g/l.

Based on their habitat and in relation to the salinity of the water, fish are usually divided into four groups: marine, freshwater, anadromous and brackish-water.

Marine fish include fish that live in the oceans and coastal sea waters. Freshwater fish live constantly in fresh water. Migratory fish move either from sea water to fresh water (salmon, herring, sturgeon) or from fresh water to sea water (some eels) to reproduce. Brackish-water fish live in desalinated areas of the seas and in inland seas with low salinity.

For fish living in lake reservoirs, ponds and rivers, it is important presence of gases dissolved in water- oxygen, hydrogen sulfide and others chemical elements, as well as the smell, color and taste of water.

An important indicator for the life of fish is amount of dissolved oxygen in water. For carp fish it should be 5-8, for salmon - 8-11 mg/l. When the oxygen concentration decreases to 3 mg/l, the carp feels bad and eats worse, and at 1.2-0.6 mg/l it can die. When the lake becomes shallow, when the water temperature rises and when it is overgrown with vegetation, the oxygen regime worsens. In shallow reservoirs, when their surface is covered with a dense layer of ice and snow in winter, the access to atmospheric oxygen stops and after some time, usually in March (if an ice hole is not made), the death, or so-called “death” of fish begins from oxygen starvation.

Carbon dioxide plays an important role in the life of a reservoir, is formed as a result of biochemical processes (decomposition of organic matter, etc.), it combines with water and forms carbonic acid, which, interacting with bases, produces bicarbonates and carbonates. The carbon dioxide content in water depends on the time of year and the depth of the reservoir. In summer, when aquatic plants absorb carbon dioxide, there is very little of it in the water. High concentrations of carbon dioxide are harmful to fish. When the free carbon dioxide content is 30 mg/l, the fish feed less intensively and their growth slows down.

Hydrogen sulfide is formed in water in the absence of oxygen and causes the death of fish, and its strength depends on the temperature of the water. At high temperature In water, fish quickly die from hydrogen sulfide.

When water bodies become overgrown and aquatic vegetation rots, the concentration of dissolved organic substances in the water increases and the color of the water changes. In swampy bodies of water (brown color of water), fish cannot live at all.

Transparency- one of the important indicators of the physical properties of water. In clean lakes, plant photosynthesis occurs at a depth of 10-20 m, in reservoirs with low-transparent water - at a depth of 4-5 m, and in ponds at summer time transparency does not exceed 40-60 cm.

The degree of water transparency depends on a number of factors: in rivers - mainly on the amount of suspended particles and, to a lesser extent, on dissolved and colloidal substances; in stagnant bodies of water - ponds and lakes - mainly from the course of biochemical processes, for example, from water blooms. In any case, the decrease in water transparency is associated with the presence of tiny suspended mineral and organic particles in it. When they get into the gills of fish, they make it difficult for them to breathe.

Pure water is a chemically neutral compound with both acidic and alkaline properties. Hydrogen and hydroxyl ions are present in it in equal quantities. Based on this property clean water, in pond farms the concentration of hydrogen ions is determined; for this purpose, the pH of the water is established. When the pH is 7, this corresponds to a neutral state of water, less than 7 is acidic, and above 7 is alkaline.

In most fresh water bodies the pH is 6.5-8.5. In summer, with intense photosynthesis, an increase in pH to 9 or higher is observed. In winter, when carbon dioxide accumulates under the ice, lower values ​​are observed; The pH also changes throughout the day.

In pond and lake commercial fish farming, regular monitoring of water quality is established: water pH, color, transparency and its temperature are determined. Each fish farm has its own laboratory equipped for hydrochemical analysis of water. necessary devices and reagents.

Biotic factors of water bodies

Biotic factors are of great importance for the life of fish. In each body of water, sometimes dozens of species of fish co-exist, which differ from each other in the nature of their diet, location in the reservoir and other characteristics. There are intraspecific and interspecific relationships between fish, as well as relationships between fish and other aquatic animals and plants.

Intraspecific connections of fish are aimed at ensuring the existence of the species through the formation of single-species groups: schools, elementary populations, aggregations, etc.

Many fish lead pack mentality life (Atlantic herring, anchovy, etc.), and most fish gather in schools only during a certain period (during the spawning or feeding period). Schools are formed from fish of similar biological condition and age and are united by unity of behavior. Schooling is an adaptation of fish to search for food, find migration routes, and protect themselves from predators. A school of fish is often called a school. However, there are certain species that do not gather in schools (catfish, many sharks, lumpfish, etc.).

An elementary population represents a group of fish, mainly of the same age, similar in physiological state (fatness, degree of puberty, amount of hemoglobin in the blood, etc.), and is preserved for life. They are called elementary because they do not fall into any intraspecific biological groups.

A herd, or population, is a single-species, different-aged, self-reproducing group of fish that inhabits a certain area and is tied to certain breeding, feeding and wintering places.

An aggregation is a temporary association of several schools and elementary populations of fish, formed as a result of a number of reasons. These include clusters:

spawning, arising for reproduction, consisting almost exclusively of sexually mature individuals;

migratory, occurring along the routes of fish movement for spawning, feeding or wintering;

feeding, formed at fish feeding areas and caused mainly by the concentration of food objects;

wintering, occurring in wintering areas of fish.

Colonies are formed as temporary protective groups of fish, usually consisting of individuals of the same sex. They are formed at breeding sites to protect egg laying from enemies.

The nature of the reservoir and the number of fish in it affect their growth and development. So, in small bodies of water where there are a lot of fish, they are smaller than in large bodies of water. This can be seen in the example of carp, bream and other fish species, which have become larger in the Bukhtarma, Kapchagai, Chardara and other reservoirs than they were before in the former lake. Zaisan, Balkhash-Ili basin and in lake reservoirs of the Kzyl-Orda region.

An increase in the number of fish of one species often leads to a decrease in the number of fish of another species. So, in reservoirs where there is a lot of bream, the number of carp is reduced, and vice versa.

Between certain types There is competition among fish for food. If there are predatory fish in the reservoir, peaceful and smaller fish serve as food for them. With an excessive increase in the number of predatory fish, the number of fish that serve as food for them decreases and at the same time the breed quality of the predatory fish deteriorates, they are forced to switch to cannibalism, that is, they eat individuals of their own species and even their descendants.

The diet of fish varies depending on their species, age, and time of year.

Feed For fish, planktonic and benthic organisms serve.

Plankton from the Greek planktos - soaring - is a collection of plant and animal organisms living in water. They are completely devoid of organs of movement, or have weak organs of movement that cannot resist the movement of water. Plankton is divided into three groups: zooplankton - animal organisms represented by various invertebrates; phytoplankton - plant organisms, represented by a variety of algae, and a special place is occupied by bacterioplankton (Fig. 4 and 5).

Planktonic organisms are usually small in size and have low density, which helps them float in the water column. Freshwater plankton consists mainly of protozoa, rotifers, cladocerans, copepods, green algae, blue-green algae, and diatoms. Many of the planktonic organisms are food for juvenile fish, and some are also eaten by adult planktivorous fish. Zooplankton has high nutritional qualities. Thus, in daphnia the dry matter of the body contains 58% protein and 6.5% fat, and in cyclops it contains 66.8% protein and 19.8% fat.

The population of the bottom of the reservoir is called benthos, from the Greek benthos- depth (Fig. 6 and 7). Benthic organisms are represented by diverse and numerous plants (phyto-benthos) and animals (zoobenthos).

By nature of nutrition fish of inland waters are divided into:

1. Herbivores, who eat mainly aquatic flora (grass carp, silver carp, roach, rudd, etc.).

2. Animal eaters that eat invertebrates (roach, bream, whitefish, etc.). They are divided into two subgroups:

planktivores that feed on protozoa, diatoms and some algae (phytoplankton), some coelenterates, mollusks, eggs and larvae of invertebrates, etc.;

benthophages that feed on organisms living on the ground and in the soil of the bottom of reservoirs.

3. Ichthyophages, or predators, that feed on fish and vertebrates (frogs, waterfowl, etc.).

However, this division is conditional.

Many fish have a mixed diet. For example, carp is omnivorous, feeding on both plant and animal food.

Fish are different by the nature of egg laying during the spawning period. The following ecological groups are distinguished here;

lithophiles- reproduce on rocky soil, usually in rivers, on currents (sturgeon, salmon, etc.);

phytophiles- reproduce among plants, lay eggs on vegetating or dead plants (carp, carp, bream, pike, etc.);

psammophiles- lay eggs on the sand, sometimes attaching them to the roots of plants (peled, vendace, gudgeon, etc.);

pelagophiles- spawn eggs into the water column, where they develop (carp, silver carp, herring, etc.);

ostracophiles- lay eggs inside

the mantle cavity of mollusks and sometimes under the shells of crabs and other animals (gorchaki).

Fish are in complex relationships with each other; life and their growth depend on the state of the reservoirs, on the biological and biochemical processes occurring in the water. For artificial breeding fish in reservoirs and to organize commercial fish farming, it is necessary to thoroughly study the existing reservoirs and ponds and know the biology of fish. Fish farming activities carried out without knowledge can only cause harm. Therefore, fishery enterprises, state farms, and collective farms must have experienced fish breeders and ichthyologists.

Every self-respecting fisherman knows for sure that in the world of fish there is huge variety. In terms of their structure, these living creatures belong to chordates, but the types of fish range from small to large, from marine to river, and so on. In this article we will talk about what types of fish are, where they live and what is typical different types. We hope you find this information useful!

A little about fish

Fish are aquatic vertebrate gnathostomes that breathe through gills. They can live in almost any body of water: salty and fresh, from streams to oceans. As mentioned above, fish belong to the chordate type, since they have an internal skeleton along the axis, the so-called chord.

Waterfowl species worldwide numbered more than 34 million a few years ago. In science there is a special section devoted to the study of fish. It's called ichthyology.

Types of fish

As you know, types of fish are a huge section in ichthyology. Yes, of course, scientists spend a lot of time studying these animals. Pisces are classified as mentioned above, but each fish has its own characteristics.

Physiology and anatomy of fish

All creatures included in the phylum chordate fish are covered with skin and scales (except for the rarest cases). The skin consists of two parts: the epidermis and the dermis. The epidermis produces a secretion that allows the skin to be protected. The dermis, the inner skin layer, plays a major role in the formation of scales.

Bony fish, unlike others, have a variety of types of scales. The types of fish, or more precisely, whether the fish belongs to one type or another, determine the characteristics of the scaly covering. So, sturgeons have ganoid scales. It is formed from bone plates coated with ganoin. The scales of bony fish living in our time are called elasmoid and are divided into round and serrated. The scales are arranged in such a way that the front plates overlap the rear ones. Not so long ago, scientists found that thanks to the comb surface of the jagged scales, waterfowl have increased hydrodynamic properties.

The coloration of fish has a huge range of colors; moreover, some colors are “warning”, which allows the body to be safe when near a predator. Also, colors can be pale, sandy, or sandy. It all depends on the habitat, the characteristics of the reservoirs. What types of fish, their environment, and colors.

The musculoskeletal system of a fish is its system of tissues and bones. It turns out that they previously had a third pair of gills, but then the organs evolved into jaws. Fish swim directly with the help of paired and unpaired fins. Moreover, thanks to their fins, they perform complex maneuvers.

The fins of bony aquatic animals have bony rays, while primitive ones have cartilaginous rays. Most fish use the caudal fin as their main propulsion mechanism. The spine in fish is formed thanks to individual unfused vertebrae. The process of swimming of fish occurs due to the contraction of muscles that are attached to the spine by tendons.

The musculature of fish has “slow” and “fast” muscles. They have a very developed sense of touch and smell, which helps them to perfectly navigate the environment where they are and avoid unfavorable places. Most chordates have a 2-chambered heart, a circulatory system, and a closed circulatory system. Blood circulates through the gills and body tissues from the heart.

Feeding in these living creatures occurs as follows: fish capture food, holding it with their teeth. Food from the mouth goes to the throat, then to the stomach, where it is processed by enzymes from the gastric juice. Fish have a wide choice of food. They can eat plankton, crumbs, worms, other fry, and some even large representatives of the class. But in general, fish are herbivores, predators and deritophages. What is most interesting is that many are able to change their type of nutrition, for example, at the beginning of life they eat earthworms and plankton, and in adulthood they feed on small or large representatives of the aquatic environment.

Fish have problems with pressure, for example, their pressure may be lower than the pressure of the environment, but due to the fact that these living creatures have a high urea content, this pressure is regulated.

Conclusion

Thus, we can conclude that the types of fish are very diverse, and each of them is characterized by a different structure, size, nutrition, and behavior. They are all different, and fishermen need to know everything about them before catching fish!