Bony fish (Osteichthyes) branched off from the common fish stem extremely early. Their fossil remains are found almost simultaneously with the remains of ancient cartilaginous fish already in the freshwater sediments of the Devonian. Bony fish are characterized by the following progressive structural features, which gave them an advantage over ancient cartilaginous fish.
Their lighter, stronger bony skeleton gave them an advantage in movement, as did an important new organ, the swim bladder. They developed a gill cover and a more advanced way of breathing. The primary bony fishes (Osteichthyes?5) already in the Devonian split into two groups.
One group - ray-finned, or ray-finned (Actinopterygii), evolved towards adaptation to life in open water bodies and was the ancestor of higher bony fish; cartilaginous ganoids, or sturgeons (Chondrostei), paleoniscids (Palaeoniscoidea), bony ganoids (Holstei) and bony fishes (Teleostei). They are characterized by the presence of a dorsal swim bladder, which serves as an important device for swimming, highly developed organs of vision and the cerebellum of the brain. The most advanced in this regard, the youngest group of bony fish (Teleostei) appeared only at the end of the Triassic and very quickly achieved complete dominance in all water bodies of the globe, both marine and freshwater (out of 20 thousand species of all fish, about 19.5 thousand belong to bony fish).
Another group of ancient bony fishes inhabited the coastal zones of freshwater bodies of water and were characterized by adaptation to life in coastal thickets; their fins are adapted to support the body at the bottom, there is a heavy scaly cover of complex ganoid or cosmoid scales, the organs of vision and the cerebellum are poorly developed, in addition to gills, they have developed abdominal swim bladders as additional respiratory organs. The presence of choanae was found in the skull, indicating the presence of pulmonary respiration, so they are currently combined into a general subclass of choanae (Choanichthyes, or Sarcopterygii).
This group of fish includes cross-finned fish (Crossopterygii) and lungfish (Dipnoi). Of the lobe-finned animals, one group (Rhipidistia) became extinct in the Permian period, and the other (Coelacantini) survived to the present day in the form of relicts (Latimeria). Lungfishes branched off from common ancestors with lobe-finned fish back in the Devonian and continue to exist in the form of relics to this day (Ceratodus - in Australia, Lepidosiren - in America and Protopterus - in Africa).
The African polypterus, or Polypterus, is very close in lifestyle to lobe-finned fish. However, many ichthyologists consider this similarity to be convergent and, based on the presence of ganoid scales in Polypterus, consider Polypterus to be related to fossil paleonistids. Together with cartilaginous ganoids, they are included in the group of ancient ray-finned fish (Paleopterygii). Recently, multifeathers have been classified as an independent subclass Brachiopterygii.
According to paleontological data, the ancient group of cross-finned fish (Rhipidistia) was the ancestor of the ancestors of terrestrial vertebrates, and the branch of primary tetrapods (Quadrupeda) was derived from this group of fish in the Devonian period. They had fleshy fins adapted for crawling along the bottom, and a skull structure very similar to the skull of the oldest fossil amphibians - stegocephalians.
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Good afternoon, my dear reader, today I will tell you about a sensation that occurred in the modern world of science, the culprit of which was an ancient animal living in the aquatic environment - the lobe-finned fish, nowadays caught by ordinary fishermen off the Comoros Islands of the Indian Ocean.
These ancient fish were thought to have gone extinct fifty million years ago!
But since this living fossil in the form of a fish was caught, it means it is alive and floating somewhere in the ocean today. Once you catch one fish, there must be more. But where to look for them?
Apparently, in the same area where she was caught - in the southwestern part of the Indian Ocean.
Scientists know that lobe-finned fish as a species appeared during the Devonian period of the Paleozoic era 405 million years ago, and became extinct in the Tertiary period of the Cenozoic era 70 million years ago. Huge fossil remains of these ancient creatures are still found throughout our planet, because lobe-finned fish gave rise to the first animals.
From a small museum in South Africa, Professor D. Smith was sent a letter with a photograph of an unusual aquatic creature, which said that this unusual fish
was caught by local fishermen, who had been catching and eating them for a long time.
Professor John Smith sat at the table and looked at the drawing he had just taken from the letter he had received. How to believe this? The drawing showed a strange fish, but what kind? It's impossible to make a mistake. 
What other fish do you see with a three-lobed tail and such strange pectoral and pelvic fins, more like flippers than the fins of ordinary fish?
Smith decided that modern lobe-finned fish should live among reefs, in the raging water of the surf and breakers. Her heavy, clumsy body, covered with strong scales, was very suitable for such a life.
From that moment the search for her began. Smith wrote to fishermen and local naturalists living on the southeast coast of Africa and Madagascar, asking and promising a large payment for the caught specimen of fish... 
And then he was informed that one lobe-finned fish, one and a half meters long and weighing 85 kilograms, had been caught in the Comoros Islands. So in 1955, eight more pieces were mined, one even with caviar. It turned out that local residents have long been familiar with this strange fish:
- she sometimes got caught in fishing nets,
- It was even possible to catch it with a fishing rod.
Only scientists did not know it, and when they learned about its existence, they did not immediately believe their eyes.
The fish was called coelacanth. Professor Smith gave it this name in honor of Miss Latimer, the curator of the museum, who sent him a letter with a drawing of a mysterious fish.
History of the origin of modern coelacanth
What is so special about this modern coelacanth fish?
The most ancient of terrestrial vertebrates are. Fish were the first vertebrates to appear on earth. Obviously, among the fish we need to look for the ancestors of amphibians - for example, frogs.
What is needed for a fish to live on land? She needs air breathing organs and limbs suitable for moving on land.
Have such strange fish ever lived on Earth? Of course they did, about four hundred million years ago.
Their swim bladder worked like lungs, but these fish also had gills - respiratory organs under water. Their pectoral and pelvic fins had a special structure: they had strong bone supports and were very different from the fins of crucian carp or bleak, because relying on them, the fish could crawl. 
But such a lobe-finned fish is more like a coelacanth, because it is one of the lobe-finned fish, and coelacanth is a coelacanth. This does not mean that the coelacanth, which has survived to this day, is the great-grandmother of newts and frogs. No!
The coelacanth has a swim bladder that is ossified and does not function like a lung. It can only breathe through gills and cannot survive even a day on land. The ancestor of frogs and newts must be sought among the long-extinct cross-legged birds, distant relatives of the coelacanth, that is, lobe-finned animals.
To transform into amphibians, fish had to leave the water. Why did they leave the water and get to land? Not in order to breathe air, because for this it was enough to pull your head out of the water.
Maybe they were fleeing from enemies who were bothering them in the aquatic environment? Hardly. Kistepers were predators and not small fish: on average a meter long. In fresh water in those days they had no enemies. So there was another reason. Most likely, they were driven out of the water by drought.
Structural features of lobe-finned fish
Resurrected from the depths of the water, the oldest lobe-finned fish, the coelacanth, has been preserved due to the fact that it lives deep under water, where it spends most of its life at a bottom depth of a thousand meters.
An adult individual can sometimes reach a length of five meters and a weight of several hundred kilograms, which is why it is inactive, although it is a fairly serious aquatic predator with large and sharp conical-shaped teeth.
The huge fish moves with the help of six large and strong paired fins, one dorsal fin and a powerful three-lobed tail, which have a certain mobility, at the base of which there are developed powerful muscles.
The fleshy skeleton of the fins has branched brushes of segments, reminiscent of animal paws when moving. It was the unusual structure of the fins that gave these fish such a unique name - lobe-finned fish.
The huge skull of the coelacanth fish is filled with a small amount of brain in the form of a fat-like substance,
and the scaly body is covered with bony plates having a round rhombic shape.
This unusual structure of lobe-finned fish also indicates that sexual maturity in these fish occurs quite late, when the female is over 20 years old, and the reproductive process is so rare that it occurs once every few years.
The lobe-finned fish coelacanth has a complexly developed reproductive system and reproduces in an ovoviviparous manner.
After internal fertilization, the female's pregnancy lasts approximately 13 months, where several embryos develop in the yellow sac in the oviduct. However, the female gives birth to only one small cub measuring 33 centimeters in size. 
Unlike modern representatives of these fish, ancient lungfishes were freshwater and had both gill and pulmonary respiration; this transitional form of existence gave them the opportunity to breathe easily both in water and on land.
The structural features of lobe-finned fish allow them to hide in the bottom shelters of the aquatic environment during the daytime, protecting themselves from bright sunlight during the day, leading a sedentary lifestyle.
However, in the dark hours of the night, these huge predators prey on smaller fish and squid. They themselves can also become victims of larger inhabitants of the deep waters, such as predatory sharks. 
The characteristics of lobe-finned fish indicate that these ancient ancestors of amphibians, lobe-finned fish, grow quite slowly and live quite long. Nowadays, this prehistoric representative of fish is a full-fledged inhabitant of the world's oceans.
Since the discovery of these fish, many specimens have been caught; today their population is about five hundred individuals, so catching them is carried out only for scientific purposes. People began to take care of these aquatic living fossils, took them under protection and included them in the World Red Book.
During the Devonian period
Geologists call the time of appearance and flourishing of lobe-finned fish the Devonian period. Life was not easy for the inhabitants of fresh waters then. Droughts replaced one another, rivers and lakes became shallow and dried up.
If the water in the shallowed lake deteriorated, then many cross-cutters could breathe atmospheric air. But if the lake dried up to the bottom, then the fish had a bad time:
- I had to crawl somewhere,
- look for new sources of water.
The fins of lobe-finned fish, similar to flippers, were weak and clumsy, but still suitable for crawling on land. Such an ancient animal could crawl out of a dry lake, crawl and get to the water.
As soon as I started to crawl out of the water, changes immediately appeared. Life on land required a different body structure and different habits. Only a few of the Kisteppers were able to adapt to this new, land-based life. The less volatile and less hardy ones died. Someone moved to the seas, since there was always water here. 
During the Devonian it was dry, and the first ancient amphibians, descended from lobe-finned fish, did not stay on land for long: they only crawled
- from lake to lake,
- from river to river.
The Carboniferous period (300 million years ago), which replaced the Devonian, was characterized by a humid climate. In the damp thickets of ferns and horsetails, among the vast swamps, the amphibious representative of the ancient lobe-finned fish did not feel bad at all.
Little by little he lost his scales, his skin became soft and slimy. The fins turned into five-fingered legs, and a thick tail appeared. Their tadpole larvae lived in water and breathed through gills. 
As in modern frogs and newts, a tadpole hatches from the eggs of amphibians. It has a tail and breathes through gills. He retained these features from his ancient ancestors.
What about coelacanth? This ancestor of amphibians is one of those that moved from fresh water to sea water. Such fish were not threatened by drought; they did not need to crawl onto land. They remained fish.
Although scientists believed that the ancient lobe-finned fish became extinct long ago, despite this, only one species of lobe-finned fish has survived to this day - the coelacanth. It is not in the direct line of ancestors of amphibians, and therefore reptiles, mammals, and, of course, humans.
She is only a distant relative of the transitional form of cross-steppers - the ancestors of amphibians. But to see even such distant relatives alive - isn’t it wonderful? That is why coelacanth turned out to be a huge event in the history of science. It's not every day you see such a living fossil.
And that’s all for today and thank you for your attention, my precious reader. I hope you enjoyed my article about the living fossil of the Paleozoic era, the lobe-finned fish coelacanth. Now you know almost everything about it, where it lives and what it looks like.
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Lobe-finned fish are one of the most ancient species of fish, which were considered extinct 70 million years ago. But in 1938, a sensation occurred - scientists accidentally learned that one of the oldest of the ancient lobe-finned fish was still alive on Earth. They called this living “fossil” fish, “resurrected” from the depths of the sea, coelacanth, studied, described and took it under protection.
Lobe-finned fish (Crossopterygii) - a superorder of lobe-finned fish - are the oldest group of fish. Until the beginning of the 20th century, lobe-finned fish were considered extinct in ancient times - 70 million years ago, but in 1938 an unusual fish was caught and scientists recognized it as an ancient lobe-finned fish. Coelacanth, as the fish was named, is the only representative of lobe-finned fish that has survived to this day. Coelacanth lives only in the area of the Comoros Islands at a depth of 400-1000 meters.
Lobe-finned fish appeared 406-360 million years ago and became extinct about 70 million years ago, scientists believe. Their fossils have been found in marine and fresh waters all over the planet. From the order of lobe-finned fishes, scientists distinguish 17 families. The fish had a length from 7 cm to 5 meters and were inactive. Lobe-finned fish had numerous conical teeth, which makes them serious predators.
Lobe-finned fish spent most of their time on the bottom, along which they moved with the help of fins.
The unusual structure of the fins gave the fish its name. As a result of moving along the bottom, these fish developed powerful muscles at the base of their fins. The skeleton of the fleshy fins consisted of several branched, brush-shaped segments, so scientists gave these “fossil” fish the name “lobe-finned.”
Modern scientists believe that the first amphibians came from freshwater lobe-finned animals, which came to land and gave rise to terrestrial vertebrates. This version of the emergence of living creatures from the sea onto land in the scientific world is not unambiguous and not indisputable, but the fact that a number of lobe-finned fish, for example, Tiktaalik, had a number of transitional characteristics that bring them closer to amphibians is a proven fact. Freshwater lobe-finned fish, for example, had double breathing: gill and pulmonary.
Science highly appreciated the merits of lobe-finned animals in the evolution of terrestrial animals: they ran along the bottom of the world's oceans, transformed, turned on their “second wind,” came ashore and gave us land animals a chance. But, having given land life to other creatures, they themselves, like dinosaurs, became extinct.
A real sensation was a live lobe-finned fish, which was accidentally caught in 1938 in South Africa at the mouth of the Halumne River at a depth of 70 m. The fish had a length of about 150 centimeters and weighed 57 kilograms. Professor J. Smith classified it as a coelacanth and in 1939 published a description of the new species. A new species of fish belonging to extinct “fossil” fish has been named coelacanth(Latimeria chalumnae), in honor of the museum curator Miss Courtenay-Latimer, who donated the first specimen of the fish to scientists. Later they found out that local fishermen had already caught lobe-finned fish and eaten them before. 
After the sensational discovery, everyone rushed to look for lobe-finned fish. And they found it! A population of 500 individuals of lobe-finned fish was discovered near the Comoros Islands. Nowadays, catching fish is allowed only for scientific purposes, and only about 200 specimens have been caught. People protect lobe-finned fish: it would be a crime to destroy a fish of ancient origin that was considered extinct and “resurrected.” Coelacanth is taken under protection and included in the International Red Book.
Coelacanths live at a depth of 180-220 m. Like their distant ancestors, coelacanths are convinced predators, and in confirmation of this they have many sharp teeth in the oral cavity. During the day they usually hide in shelters and at night they hunt for fish and squid. The coelacanths themselves can become victims of hunters who are “more predatory” than them - large sharks.
The largest specimens of these coelacanths caught are 1.8 m long and weigh 95 kg. Scientists report that coelacanths grow slowly, but fortunately live for a long time. These living “relics” are not much different from the Mesozoic fossil coelacanths - their extinct cousins. The fish have a powerful tail and strong mobile paired fins, but the skull is filled with a fat-like substance, and the brains occupy no more than 1/1000 of its volume.
Coelacanth has 7 fins, 6 of them are strong, strong, well developed, resembling limbs (paws). During movement, the coelacanth stands on these paired fins and, fingering them like paws, moves. However, coelacanths lead a sedentary lifestyle, spending almost all their time at the bottom of the sea.
Coelacanths are ovoviviparous. Their bright orange eggs are 9 cm in diameter and weigh up to 300 g. Pregnancy in coelacanths lasts about 13 months, and large eggs have a characteristic bright orange color. The body length of newborn cubs reaches 33 cm.
The coelacanth's body cavity contains a degenerated lung, but coelacanths completely lack internal nostrils and cannot breathe atmospheric oxygen. The entire body of these lobe-finned fish is covered with scales - bony plates of rhombic or round shape.
Scientists studying coelacanths, the descendants of the most ancient fish, have come to the conclusion that the ancient lobe-finned fish went in two directions in their development. The first way is the emergence of coelacanths. This line has survived to our time and appears before us in the guise of coelacanth. Other lobe-finned animals adapted to breathing in the air and crawled onto land on their strong, mobile fins; their descendants are probably terrestrial vertebrates.
These fish do not tolerate bright daylight and living outside the depths of the sea. However, in 1972, scientists managed to relocate a guest from the “past” to a research laboratory on the island of Madagascar. It was a small coelocanthus that weighed 10 kg and had a length of 90 cm. A unique living specimen of the lobe-finned fish lives in an aquarium in the capital of Denmark, Copenhagen. In 1986, Japanese scientists showed coelacanth on television. A unique film was shot: filming took place at a depth of more than 50m in the Indian Ocean near the Comoros Islands.
General characteristics of the FISH superclass
Ichthyology.. This is the largest in the number of species (more than 20 thousand) and the most ancient group of primarily aquatic chordates. Fish inhabited all types of marine, fresh and brackish water bodies. Their entire organization bears the imprint of adaptation to life in a dense aquatic environment. The main features of their organization are the following: The shape of the body is streamlined due to the smooth transition of its sections - head, body and tail - into each other and flattened laterally. The skin is rich in glands that secrete mucus abundantly and is covered with scales. The organs of movement and stabilization of the body position with the back up are unpaired and paired fins. The buoyancy of bony fishes is maintained by a hydrostatic organ - the swim bladder. The skeleton is cartilaginous or bone. The skull is fixedly connected to the spine. The spine has two sections: trunk and caudal. The limb girdles are not connected to the axial skeleton. The muscles are poorly differentiated and segmented. Body movements are monotonous, serpentine and predominantly in the horizontal plane. Captures food actively using the jaws. The anterior and middle parts of the intestine are highly differentiated. Digestive glands are developed: liver and pancreas. Respiratory system-gills. Circulatory system closed, has one circle of blood circulation and a two-chambered heart. The organs and tissues of fish are supplied with arterial blood. Excretory organs- paired trunk buds. The final product of nitrogen metabolism, excreted from the body, is ammonia or urea. central nervous system represented by the brain and spinal cord. The brain is differentiated into five sections. The structure of the sense organs - vision, smell, hearing - is adapted to functioning in the aquatic environment. A special lateral line organ has been developed, allowing fish to navigate water currents. Fish are dioecious; many are sexually dimorphic. Reproduction is only sexual. For most, fertilization is external, in water. Development with incomplete metamorphosis (with the larval stage).
The first remains of fish are known only from the Late Silurian. The Lower Devonian sediments contain clear remains of various groups of fish. The formation of the superclass of fish - in the beginning, middle of the Silurian. Fish appeared in fresh water bodies, and only then penetrated into the seas. The paucity of fossil remains of fish does not allow us to trace the origins of individual groups. For 400-450 million years, evolution proceeded in complex ways: numerous groups became extinct. Many stood far from each other. Fish separated from the primitive heteroscutaneous jawless fish around the beginning of the Silurian. Two groups evolved from unknown primitive gnathostomes: armored and maxillobranched. The armored class included small and medium-sized fish; their heads were covered with a shell made of bony plates. They lived in rivers. But at the beginning of the Devonian, marine ones appeared. They ate invertebrates. They became extinct by the end of the Devonian. Maxillobranchs had medium body sizes. They became extinct by the middle of the Permian period. Cartilaginous fish separated from some primitive maxillobranchs at the beginning of the Devonian. At the beginning of the Silurian, bony fish with fast currents separated from another group of primitive maxillobranchs, which contributed to the formation of a bony skeleton - the ability to support their fins on the ground. Teeth and body imprints of shark-like cartilaginous fish were discovered in Middle Devonian sediments. They lived in the seas and were small and medium in size. The body is covered with placoid scales, the skeleton is cartilaginous, there are more than 5 gill arches, the mouth is almost at the end of the muzzle. They became extinct by the end of the Carboniferous period. By the end of the Devonian, true shark fish became isolated. Covered with placoid scales, the skeleton of the fins differs; in males, the section of the ventral fin is transformed into a copulatory organ, cartilaginous vertebral bodies appear, the structure of the teeth becomes more complex, they lived in the seas, ate fish. There is a difference between sharks and rays. In the sediments of the Carboniferous period, the remains of marine bottom fish were found; they fed on mollusks, had a flattened body and large pectoral fins. The upper jaw is attached to the skull. The teeth were flattened and merged into bone plates. They were combined into the group of bradyodonts. They separated themselves from some primitive shark-like fish. In the Permian period, bradyodonts died out, but from the end of the Triassic there were remains of chimeras - descendants of bradiodonts. At the end of the Silurian, bony fish became isolated. Due to the lack of remains, the initial stages of evolution cannot be traced. In the Devonian, representatives of both subclasses emerged: lobe-finned and ray-finned, which had common ancestors. Lobe-finned had fleshy bases of paired fins, an internal skeleton with a central axis, into which the radial was attached from the sides. The tail is heterocercal. Some species develop internal nostrils. Ossification of the skull. Some forms retain the notochord. Lobe-finned fish were divided into 2 superorders: 1) Lobe-finned fish - predatory fish with well-developed teeth, inhabitants of fresh waters. They were divided into two orders: repidistiformes and coelocanthaceae. Repidistiformes - lung development occurs. They separated in the mid-Devonian from one of the freshwater groups of primitive amphibians. Repidistias became extinct due to fierce competition. Coelocanthaceae - moved to the seas. At the end of the Paleozoic they were a large group. Separated from the repidists. Choanae and fins with elongated blades were absent. The swim bladder is poorly developed. In the Triassic they began to fade away; in the Jura and Cretaceous they became less common. Not found in later layers. They were considered extinct. In 1938, an unknown fish was found off the coast of South Africa. John Smith identified it as a coelacanth - coelacanth halumne. They live near the Camoros Islands, at a depth of up to 300 meters, feed on fish, their numbers are small. From 1m. The notochord is well developed, the brain occupies 0.01 of the braincase. The bubble has been reduced. The intestine has a well-developed spiral valve. Ovoviviparous, low fertility. A relict species, preserved due to a combination of favorable conditions. 2) Lungfishes - known from the Middle Devonian, close to lobe-finned fishes - a lateral, highly specialized branch. Never been numerous. They feed on sedentary tunicates. The presence of lungs is found in the Paleozoic in all inland waters. By the end of the Paleozoic they began to die out. 3 genera have survived to this day. Subclass ray-finned - paired fins lack fleshy bases, the skeleton does not have an axis. The tail is hetero- or homocercal. No squamosal bone. The ancient forms retained the notochord. The notochord took on the appearance of a rosary. The skull was ossified. In young groups, several ossifications are formed. Formation occurs in rivers with fast currents. Ability for intense maneuverable swimming. They penetrated into different types of water bodies and are distributed throughout the seas. Fossils from the Middle Devonian – Europe, Asia. In the Permian period - everywhere. The diversity of fossil and modern groups of fish, their long and complex evolution, the incompleteness of the chronicle, and insufficient study of individual groups leads to the fact that the classification of fish is very complex and is still not sufficiently diverse.
16. General characteristics of cartilaginous fish. CARTILIATED FISHES (Chondrichthyes), the class includes two subclasses: elasmobranchi fishes (Elasmobranchii) and whole-headed fishes (Holocephali). The class unites about 800 species, divided into 12-15 orders. Cartilaginous fish are jawed animals; their jaws are formed by the bones of the first gill arch. The subclass elasmobranchs unites most of the modern cartilaginous fish and includes about 750 species of sharks and rays. In these fish, gill filaments in the form of plates are located on the leathery partitions between 5-7 pairs of gill slits (hence the name). There are no gill covers. Sharks have gill slits on the sides of their heads, while stingrays have gill slits on the ventral side. Many elasmobranchs have a small paired opening, which is a rudiment of another gill slits (squirt). Whole-headed fish have four pairs of gill slits and no squirter. Cartilaginous fish have a pronounced snout - rostrum. The skeleton is cartilaginous, scales, if present, are placoid. Sharks have an elongated body, torpedo- or spindle-shaped. The upper lobe of the powerful caudal fin is much more developed than the lower one, and the end of the spine extends into it (heterocercal fin). In sharks, teeth (modified placoid scales) are arranged in several rows and have the shape of sharp cones or flat triangular plates, smooth, jagged or multi-peaked. Stingrays have a strongly flattened body and a blunt, rounded snout. The pectoral fins are wide, attached at the edges to the body and head. The caudal peduncle is thin, the lobes of the caudal fin are often reduced. The anal fin is absent. Unlike sharks, which use an oscillating motion of their tail to swim, stingrays swim by flapping their pectoral fins like wings. Their teeth are spike-shaped or flattened, tightly adjacent to each other, forming a grater. The sense organs are represented by the organs of smell, vision, touch (lateral line); some species have electrical organs. All cartilaginous fish lack a swim bladder; the surface of the intestine is greatly enlarged due to the spiral valve. The heart has a conus arteriosus that increases the efficiency of blood circulation and metabolism associated with an active lifestyle. Elasmobranchs have a cloaca, which is absent in whole-headed animals. The skeleton is cartilaginous. Visceral skull, amphicoelous vertebrae. Cartilaginous fish are primarily marine animals, including inhabitants of deep water. Some species enter or live permanently in rivers. Cartilaginous fish are highly specialized animals, many are predators. Sharks are often indiscriminate in their choice of food, but some species have preferred prey items. In addition to fish, sharks eat bottom-dwelling invertebrates (crabs, sea urchins, gastropods and bivalves) and free-swimming ones (cephalopods, jellyfish). Most stingrays lead a bottom-dwelling lifestyle, spending a significant portion of their time lying on the bottom or partially buried in the sand. In this regard, their dorsal side has a dark protective color, and the ventral side is light. Their food consists of bottom invertebrates and small fish. Fertilization in all cartilaginous fish is internal. The copulatory organ of males is a pair of pterygopodia, each of which is a modified posterior part of the ventral fin. Cartilaginous fish reproduce by laying eggs, ovoviviparity, or viviparity. The eggs are often enclosed in a capsule and have outgrowths. During a live birth, the placenta is formed. Most often, the placenta is formed at the site where the yolk sac adheres to the wall of the uterus. Some spiny sharks (Squalus) and electric rays (Torpedo) additionally develop villi in the uterus - trophotenia, which supply the embryo with nutrients. For this purpose, in eagle rays and butterfly rays, long filaments are formed - trophonemes, which penetrate through the squirter of the embryo into its digestive tract. Sharks, as typical representatives of cartilaginous fish, have a reputation as bloodthirsty predators. The most dangerous for humans is the tiger shark (Galeocerdo cuvier), up to 6 m long, living in tropical and subtropical waters of all oceans.
17. Systematics of the superorder Sharks and the superorder Stingrays. Characteristics of the main representatives. Subclass Elasmobranhii. Superorder Sharks (Selachomorpha). About 20 families, 350 species. Torpedo-shaped body, heterocercal fin, gill slits on the sides of the head, chewing and cutting teeth. Representatives of the superorder are widespread in all seas and oceans. They mainly live in sea water, but some species can also live in fresh water. Most sharks are predators, but there are filter feeders; they feed on plankton, squid and small fish. Order Chlamydoselachiformes: frilled cheekbone, 6 gill slits (1 grows into a cloak), benthic, small in number, ovoviviparous, feed on mollusks and fish. Order Polybranchiformes (Hexanchiformes): large (4-8 m), 6-7 pairs of gill slits, live at great depths, feed on fish, ovoviviparous. Sevengill shark. Order Heterodontiformes: up to 1.5 m, massive head, 5 pairs of gill slits, teeth in the front part of the jaw are sharp and small, the rest are mottled, blunt, feed on crabs and mollusks, oviparous. Horned shark. Order Lamniformes: large, dangerous to humans, feed on large fish, are benthophagous, ovoviviparous. Sea fox. Order Carcarhiniformes: oviparous and ovoviviparous, from small to large. Whale shark. Order Squaliformes: there is a spine in front of each dorsal fin, up to 2 m, feed on fish, crustaceans, ovoviviparous. Katran. Order Sawtooth-like (Pristiophoriformes): found in the warm waters of the Pacific and Indian oceans, the snout is a long xiphoid process, on the sides there are large teeth, slow, bottom. Sawtooth shark. Order Squatiniformes: bottom-dwelling, flattened in the dorso-ventral direction, blunt snout, pectoral and pelvic fins enlarged, up to 2.5 m, ovoviviparous, oviparous. Angelfish. Tiger shark: reaches a length of 5 m, but larger individuals are also found. Until the shark reaches two meters in length, transverse stripes similar to those of a tiger are noticeable on its sides. These stripes camouflage these fish from their larger relatives. Then the stripes fade and fade. Adult tiger sharks are gray. Eats fish, including smaller sharks, dolphins, shellfish, turtles, sea snakes, but also carrion. The shark gives birth to 30–80 cm baby sharks. The female, ready to produce offspring, loses her appetite to avoid cannibalism. During the breeding season, female sharks gather in schools to protect their offspring from males. On average, a tiger shark gives birth to 10 to 25 pups. The tiger shark is an ovoviviparous fish. This means that embryos develop in eggs, but are released from the egg shells while still in the mother’s body. Development period - 9 months. Superorder Stingrays (Batomorpha). The body is flattened in the dorsoventral direction. The pectoral and ventral fins are highly developed. 5 pairs of gill slits are located on the ventral side. The squirts are better developed than those of sharks. Bottom-dwelling, sedentary. The caudal fin is poorly developed. The teeth are blunt and form a grater for grinding mollusk shells. Most stingrays live in seawater, but there are also several freshwater species. The upper side of stingrays is adapted in color to a particular living space and can vary from light sand to black. On the upper side there are eyes and holes into which water enters for breathing. Order Sawfish (Pristiformes): up to 6 m, body slightly flattened, snout long, sword-shaped, with teeth along the edges, found in shallow waters in the (sub)tropics, feed on small schooling fish, ovoviviparous. Order Rhinobatiformes: up to 5 m, use the tail to move, benthic, ovoviviparous. Order Rhomboids (Rajiformes): the body is strongly flattened, has the shape of a diamond, bottom-dwelling, feeds on fish. Order Myliobatiformes: up to 7 m, diamond-shaped, less often oval, sometimes with a poisonous needle on the tail shaft. Giant manta ray. Order Torpediniformes: can create current discharges of 60-300V with a force of 5A, are inactive. Manta, or giant sea devil (Manta birostris) is the largest of the rays, the body width of some individuals reaches 7 m (in most cases 4-4.5 meters). Manta rays are found in tropical waters of all oceans. The oral cavity of manta rays is very wide and located on the front edge of the head. On the sides of the mouth there are two blades that direct the flow of water into the mouth. Like other stag rays, mantas have a developed filtering apparatus, consisting of gill plates on which food is filtered - planktonic crustaceans and small fish. Mantas move beautifully in the water, flapping their “wings” - their pelvic fins - with ease and grace. Sometimes observed lying on the surface of the water. The female manta bears a single, but very large calf, about 125 cm wide and weighing 10 kg. The ability of sea devils to jump out of the water is well known. Sea devil meat is quite tasty, and the liver contains a lot of fat.
18) Cartilaginous fish (Chondrichthyes) have a cartilaginous skeleton that retains strength due to the fact that it is impregnated with calcium salts. The notochord remains throughout life, but is partially reduced. The skull fuses with the jaws (in whole-headed animals) or forms 1–2 articulations with them (in elasmobranchs). There are caudal and paired ventral and pectoral fins. The mouth is located on the ventral side and is armed with jaws with teeth covered with enamel. There are two nostrils in front of the mouth. On the outside, the body of these animals is covered with rough placoid scales formed by dentin. Each scale consists of a basal plate, a neck and a crown. In structure it is similar to the teeth of higher vertebrates; Most likely, the teeth are derivatives of placoid scales. The respiratory system begins with 5–7 pairs of gill slits. Elasmobranch fish never have an operculum. In the intestine, a spiral valve stretches along its entire length, increasing the absorption surface. The swim bladder is absent; Cartilaginous fish are forced to constantly move to avoid drowning. There is a high concentration of nitrogen-containing substances (in particular, urea) in the blood. The arterial cone of a two-chambered heart is capable of independent contraction and provides an additional impulse of blood. The sense organs are represented by the organs of smell, vision, touch (lateral line); some species have electrical organs. Fertilization in almost all cartilaginous fish is internal. Many of them have a cloaca; in males, several ventral fins form the male copulatory organ. Cartilaginous fish are viviparous or lay eggs.
19. General characteristics of the class of bony fish.
Type Chordata Chordata Subtype Vertebrates Vertebrata Group Jawed Gnathostomata Overhead. Pisces Pisces cl The bony fish Osteichthyes includes an overwhelming majority (about 20,000) species of fish. Bony fish are common in a wide variety of water bodies. The diversity of life conditions determines the richness of this group in species and their extreme diversity. Skeleton always osseous to one degree or another. Integumentary bones have the form of plates (embryonically they arise in the connective tissue layer of the skin, regardless of the cartilaginous elements of the skeleton). Ossification of the skeleton, chondral bones (cartilaginous). Interbranchial septa in the respiratory apparatus they are reduced, and the gill filaments sit directly on the gill arches. Always available bony gill cover, covering the outside of the gill apparatus. The vast majority of species have swim bladder. Embryonically, it arises as an outgrowth of the dorsal wall of the intestine. In primitive groups it retains a lifelong connection with the digestive tube. Characteristic simplification of the structure of the skeleton of paired fins: in chest And belly. Melt. There are no basalia, and in the abdomen there are also no radials. Tail. float homocercal. Cloaca is missing. swim bladder- an important hydrostatic organ: a change in the volume of gases in it changes the density of the fish’s body, this has adaptive significance when fish move from one water horizon to another. In the vast majority of bony fish external fertilization, the caviar is small, devoid of horn-like shells. Live birth occurs in a small number of species. Spiral valve in the intestine and conus arteriosus hearts only among ancient groups. Body covered bone scales. Classification is extremely difficult; nowadays there are several views on the taxonomy of this group. 2 subclasses: Ray-finned and Lobe-finned.
20) System of the subclass Lobe-finned fish. Features of the organization and lifestyle of lobe-finned and lungfishes. Lobe-finned(lat. Sarcopterygii) or Choanaceae- subclass of bony fish. An ancient group that has survived to this day. . Known since the Early Devonian (300-400 million years ago), they combine both archaic and progressive features. The basis of the axial skeleton is the elastic chord. There are no vertebral bodies, but there are upper and lower arches, the body is covered with cosmoid scales (Cosmoid scales are a bone plate, externally covered with cosmin (a modification of dentin, even more dense). By origin, cosmoid scales are a complex of fused and highly modified placoid scales.) , in the intestine there is a spiral valve, in the heart there is a conus arteriosus. At the same time, they are characterized by progressive features: lung sacs, through nostrils, fleshy lobes on paired fins. The lobe-finned superorders include the lungfish and lobe-finned. Lobe-finned fish(unlike ray-finned fish) switched to living in inland waters, in them the outgrowth of the esophagus turns into a lung, the leading analyzer is the sense of smell, and in comparison with other fish the brain changes. Musculoskeletal system. The movement is carried out using the lateral bends of the body. With the help of fins they can crawl along the bottom and crawl into another body of water. Breath. Gills and lungs. Ventilation mechanism: oropharyngeal and via gill covers. Circulatory system. Since there are lungs, a second (pulmonary, pulmonary) circulation appears. Digestion. Diverse ways to eat. There are 3 openings: genital, anal, excretory. Reproduction. Internal fertilization, a small number of eggs, can develop in the mother's body. Nervous system. The forebrain is well developed, a new cortex appears in it, and choanae (internal nostrils) appear. Moluscods-n/neg. Lungfishes. Active predators - n/neg. Lobster-finned. n/neg Lungfish. a group of freshwater fish that combines primitive characteristics with features of high specialization for life in oxygenated reservoirs. Most of the skeleton in modern representatives remains cartilaginous. The caudal plane merges with the dorsal and anal planks (dificercal). The paired limbs have a wide, fleshy blade, but are built like biserial fins. The most remarkable feature of lungfishes is the presence, in addition to gills, of pulmonary respiration. One or two pulmonary bladders that open on the abdominal side of the esophagus function as air respiratory organs. The nostrils are through, lead into the oral cavity and serve for pulmonary breathing. Blood enters the lungs through special vessels extending from the fourth pair of gill arteries. These vessels are apparently homologous to the pulmonary arteries. From the “lungs” there are special vessels that carry blood to the heart: they can be considered homologues of the pulmonary veins. The atrium has a small septum that partially divides it into left and right halves. The left side receives blood from the pulmonary veins, the right side receives all the rest of the blood from the Cuvier ducts and the posterior vena cava. It should be emphasized that the vena cava is absent in ray-finned animals and this vessel is characteristic of terrestrial vertebrates. The vena cava arises by splitting the right cardinal vein. The progressive features of lungfish also include the strong development of the forebrain. Finally, the genitourinary system is close to that of cartilaginous fish and amphibians. 1 negative Horntoothed. n/neg. Whalefin. - an ancient and almost extinct group of fish. These are predators: their mouth is armed with numerous sharp teeth. A degenerated lung surrounded by fat was found in the body cavity. Coelocanths do not have internal nostrils, and, unlike Mesozoic lobe-fins, they are not capable of breathing atmospheric oxygen. The body is covered with scales, which are thick bone plates of a round or rhombic shape, covered on top with a layer of modified dentin and a thin layer of enamel. They originally lived in fresh water bodies, in which they probably periodically experienced a lack of oxygen: in connection with this, double breathing developed. The contamination of reservoirs with dead vegetation was apparently a prerequisite for the development of peculiar paired limbs, which had muscles on the limb itself and could be used not only for rowing, but also for support on a solid substrate.
Bony fishes are the largest class of vertebrates, numbering about 20,000 species. The most ancient representatives of this class descended from cartilaginous fish at the end of the Silurian. Currently, 99% of the class belong to the so-called bony fishes, which first appeared in the mid-Triassic, but their evolution was slow for a long time and only at the end of the Cretaceous period it accelerated sharply and reached an amazing flowering in the Tertiary period. They inhabit a wide variety of bodies of water (rivers, seas and oceans down to the greatest depths; they are found in Arctic waters). Thus, bony fish are the vertebrates most adapted to living in an aquatic environment. In addition to bony fish, the class includes several dozen more species of ancient bony fish that have retained some of the features of cartilaginous fish.
general characteristics
Most species in this class are adapted for fast swimming, and their body shape is similar to that of sharks. Less fast-swimming fish have a taller body (for example, many species of carp fish). Species that lead a sedentary lifestyle on the bottom (for example, flounder) have the same flattened body shape as stingrays (Fig. 81).
Rice. 81. Bony fish:
1 - herring (family Herring); 2 - salmon (family Salmonidae); 3 - carp (family Cyprinidae); 4- catfish (family Catfish); 5- pike (family Pike); 6- eel (family Acne);
7 - pike perch (family Perch); 8 - river goby (family Goby); 9 - flounder (Flounder family)
Veils. The body length of fish varies - from several centimeters to several meters. Unlike cartilaginous and ancient bony fishes, teleosts have many small species that have mastered small biotopes that are inaccessible to larger species. The skin of the vast majority of bony fish is covered with small, bony, relatively thin scales that overlap each other in a tiled manner. They protect fish well from mechanical damage and provide sufficient body flexibility. There are cycloid scales with a rounded upper edge and ctenoid scales with small teeth on the upper edge. The number of scales in longitudinal and transverse rows for each species is more or less constant and is taken into account when determining the species of fish. In cold weather, the growth of fish and scales slows down or stops, so annual rings form on the scales, by counting which you can determine the age of the fish. In a number of species, the skin is bare and devoid of scales. There are many glands in the skin; the mucus they secrete reduces, like in other fish-like creatures, friction when swimming, protects against bacteria, etc. In the lower layers of the epidermis there are various pigment cells, thanks to which fish are hardly noticeable against the background of their environment. In some species, body color can change in accordance with changes in the color of the substrate. Such changes are carried out under the influence of nerve impulses.
Nervous system. The size of the brain in relation to the size of the body is somewhat larger than that of cartilaginous fish. The forebrain is relatively small compared to other parts, but its striatum is large and, through their connections with other parts of the central nervous system, influences the implementation of some rather complex forms of behavior. There are no nerve cells in the roof of the forebrain. The diencephalon and the pineal and pituitary glands separated from it are well developed. The midbrain is larger than other parts of the brain; in its upper part there are two well-developed optic lobes. The cerebellum of well-swimming fish is large. The size and structure of the medulla oblongata and spinal cord have increased in size and complexity. The subordination of the latter to the brain has increased compared to what is observed in cartilaginous fish (Fig. 82).
Rice. 82. Perch brain:
1 - olfactory capsule; 2 - olfactory lobes; 3 - forebrain; 4 - midbrain; 5 - cerebellum; 6 - medulla oblongata; 7 - spinal cord; 8 - orbital branch of the trigeminal nerve; 9 - auditory nerve; 10 - vagus nerve
Sense organs. There have been some complications in the sense organs. Seismosensory organs are located in the canals of the lateral walls of the body and form a dense network on the head. The round sac of the labyrinth is more developed, and contrary to the long-held opinion that bony fish perceive only rough environmental shocks, numerous experiments have proven that they respond to a variety of sound vibrations and use them to communicate within the population. The ability to perceive various chemical irritations is very well expressed. Many species perceive even slight changes in temperature in the water around them. The vision of bony fish is designed, like that of other fish, for close range; The lens is spherical, unable to change its curvature, the sharpness of the image is achieved by moving it using the contraction of a special muscle - the falciform process.
Skeleton. During the evolution of the class under consideration, the skeleton gradually ossified. The notochord was preserved only among the lower representatives of the class, the number of which is insignificant. When studying the skeleton, you need to keep in mind that some bones arise as a result of the replacement of cartilage with bone tissue, while others develop in the connective tissue layer of the skin. The former are called the main bones, the latter - the integumentary bones.
The brain section of the skull is a box that protects the brain and sense organs: smell, vision, balance and hearing (Fig. 83).
Rice. 83. Diagram of the arrangement of bones in the skull of a bony fish. The visceral skeleton is separated from the cranium. The operculum is not drawn. The main bones and cartilage are covered with dots, the integumentary bones are white:
/ - angular; 2 - articular; 3 - main occipital; 4 - main wedge-shaped; 5 - copula; 6 - dental; 7 - lateral olfactory; 8 - external pterygoid; 9 - internal pterygoid; 10 - lateral occipital; 11 - frontal; 12 - pendants; 13 - hyoid; 14 - ossified ligament; 15 - lateral wedge-shaped; 16 - middle olfactory; 17 - posterior pterygoid; 18- maxillary; 19 - nasal; 20 - oculocuneiform; 21 - parietal; 22 - palatal; 23 - premaxillary; 24 - parasphenoid; 25 - square; 26 - upper occipital; 27 - additional; 28 - opener; 29-33 - ear bones; I-V - gill arches
The roof of the skull is formed by paired nasal, frontal, and parietal bones. The latter are adjacent to the superior occipital bone, which, together with the paired lateral occipital bones and the basioccipital bone, forms the posterior part of the skull. The bottom of the skull consists (from front to back) of the vomer, the parasphenoid (a wide, long bone very characteristic of a fish skull), and the sphenoid bone. The front part of the skull is occupied by a capsule protecting the olfactory organs; On the sides there are bones surrounding the eyes, and a row of bones (usually 5) protecting the organs of hearing and balance.
The visceral part of the skull consists of a number of bony gill arches, which support and protect the gill apparatus and the anterior part of the digestive system. Each of the mentioned arches includes several bones. Most fish have 5 arches to which the gills are attached (on each side). Below, the gill arches are connected to each other, and the anterior one is connected to the hyoid arch, which consists of several bones. The upper of these bones, the hyomandibular bone (hyomandibular bone), is attached to the medulla of the skull in the area of the auditory region and is connected through the quadrate bone to the bones surrounding the oral cavity. Thus, the hyoid arch serves to connect the branchial arches with the rest of the visceral region, and its upper bone with the medulla of the skull.
The edges of the mouth and the entire oral cavity are reinforced by a number of bones. The maxillary row of bones is represented (on each side) by the premaxillary and maxillary bones. Next comes a series of bones: the palatine, several pterygoids and the quadrate. The quadrate bone is adjacent to the suspension (hyomandibular) at the top, and to the lower jaw at the bottom. The latter consists of several bones: the dental (the largest), the angular and the articular, connecting to the quadrate. In ancient fish (which still had a cartilaginous skeleton), all arches of the visceral part of the skull bore gills, and later the anterior ones of these arches turned into hyoid arches and jaw rows of bones.
The spinal column consists of a large number of biconcave (amphicoelous) vertebrae, in the spaces between which remains of the notochord are preserved. A long spinous process extends upward and somewhat backward from each vertebra. The bases of these processes are separated, and they form a canal through which the spinal cord passes. Two short transverse processes extend from the lower side of the vertebral bodies, to which long curved ribs are attached in the trunk region. They end freely in the muscles and form the frame of the side walls of the body. In the caudal part of the body, only the lower spinous processes extend downward from the vertebrae.
Organs of locomotion. In bony fish, as in cartilaginous fish, they are represented by unpaired (dorsal, anal, caudal) and paired (pectoral and ventral) fins. The fin blades are supported by bony rays. Some rays are soft, consisting of a number of bony sections, others are hard, solid, the ends of which are pointed in many species. The rays of the dorsal and anal fins rest on bones - basalia (fin supports), lying in the muscles at the edge of the body. Paired fins rest on limb girdles lying between the muscles: pectoral - on the shoulder (or anterior) girdle, consisting of several bones, the upper of which is attached to the skull (Fig. 84), abdominal - on the pelvic (or posterior) girdle, consisting of usually made from a pair of bones.
Rice. 84. Belt of forelimbs and pectoral fin of ray-finned fish:
/ - primary belt; 2 - blade; 3 - coracoid; 4 - basal elements; 5 - radials; 6 - skin rays
The rays of the caudal fin rest on the back of the vertebral column. In lower bony fish (as in cartilaginous fish), the caudal fin is heterocercal, the upper lobe of which is much larger than the lower lobe. In bony fishes, the caudal fin is homocercal, since both its blades are approximately equal.
The gradual ossification of the skeleton was of great adaptive importance in the evolution of fish, since it contributed to the development of strong support for muscles and reliable protection of the central nervous system and internal organs. Since the bone skeleton can include a large number of small bones, this was an important condition for the emergence of many species with a small body size.
The bony skeleton has a greater mass than the cartilaginous one, which could make it difficult for the fish in question to swim. Therefore, the latter developed, by branching from the anterior part of the intestine, a swim bladder lying above the intestine and filled with a mixture of gases (nitrogen, oxygen and carbon dioxide), due to which the body weight of the fish was significantly reduced. In primitive species of bony fish (open-vesical fish), the bladder remains connected to the intestinal tube throughout life. In most species (closevesical), which appeared later, it is completely separated from the intestine. The walls of the bladder contain dense plexuses of capillaries, which ensure its filling with gases. The volume of gases in a closed space, as is known, can greatly decrease during compression and, conversely, increase sharply when compression decreases. The increase and decrease in the volume of the bladder occurs due to the work of the muscles surrounding the abdominal cavity. Therefore, the swim bladder not only reduces body weight, but also plays a hydrostatic role, that is, it facilitates the rise of the fish upward when it expands and the dive when it contracts. The swim bladder was reduced in a number of fish species that lead a sedentary lifestyle on the bottom, and in those species that, having strong muscles, are able to quickly move upward or deeper. The presence of a bubble in the latter could cause, during a rapid rise, a strong expansion of it and inversion of the insides, as has been proven by many observations. In some fish, the swim bladder, connected by a series of bones (Weberian apparatus) to the labyrinth, helps transmit some sound waves to the latter.
Digestive system. Most bony fish have some peculiarities. There is no spiral fold; the intestinal surface increases due to its elongation. In addition, pyloric processes extend from the initial part of the intestine in many higher bony fishes, which also increase the surface of the intestine. Excreta is removed through the anus; there is no cloaca. The structure of the system under consideration varies depending on the nature of the power supply. Predators that attack other fish and larger invertebrates have a wide mouth, usually lined with large, sharp teeth; the stomach is large, sharply separated from the esophagus and the beginning of the intestine, the total length of the intestine is much shorter than in herbivorous species. In the latter, and especially in species that feed on small invertebrates and organic remains, the teeth are small or absent; the stomach is almost indistinct or absent. Cyprinids and some other fish have special pharyngeal teeth in their pharynx for mechanical processing of food. The liver is well developed, although it does not reach the same size as in many cartilaginous fish. The pancreas is represented by separate lobules located in the liver or in the walls of the initial part of the intestine, i.e., it does not yet have a compact shape, but is better developed than in cartilaginous fish.
The study of the composition of food of different fish, especially commercial fish, is of great practical importance, since if there is information about the qualitative and quantitative composition of the organic world of certain water bodies, it allows us to find out which species and in what quantity can live in each of them, with what combination of species the food supply reservoirs can be fully used without prejudice to its subsequent restoration, etc. These issues are specially studied in courses on fish farming.
Respiratory system. The main organs of the respiratory system are the gills, consisting of many petals attached at their proximal ends to the gill arches, in contrast to the gill plates of cartilaginous fish, attached on one side to the interbranch septa. Consequently, the surface area of the gills of bony fishes is much larger than that of cartilaginous fishes. The mechanism of inhalation and exhalation is also more advanced. A fairly significant portion of gas exchange (on average about 10%) occurs through the skin. The swim bladder and some parts of the intestine can take part in gas exchange.
Circulatory system. The heart consists of an atrium and a ventricle. There is only one circulation. Teleost fish do not have an arterial cone, and the arterial vessel extending from the ventricle begins with the aortic bulb. The number of erythrocytes is significantly greater than in cartilaginous fish, which increases the intensity of dissimilation processes. The spleen is well developed (Fig. 85).
Rice. 85. Opened perch (female):
/ - gills; 2 - heart; 3 - liver; 4 - swim bladder; 5 - spleen; 6 - ovary; 7 - stomach; 8 - pyloric appendages; 9 - intestine; 10 - bladder; 11 - anal opening; 12 - urogenital opening; 13 - rakers of the gill arch
Excretory system. In the excretory system, a special role is played by the trunk buds, located in the form of two long dark red narrow ribbons along the spinal column. The distal ends of the ureters (Wolffian canals) join and open outward through a common opening at the back of the anus. The bladder arises from the distal part of the fused ureters.
Reproduction. The reproductive system of bony fishes is simplified compared to cartilaginous and ancient bony fishes, but is capable of producing a large number of gametes. Two elongated testes (often called milts) are located under the kidneys on the sides of the swim bladder. The seed does not exit through the Wolffian canal, but through a short tube formed by the membrane of the testis. Both vas deferens open outward through a common genital opening behind the anus and urinary openings or a common genitourinary opening. During the breeding season, the ovaries (usually two of them) are voluminous sacs filled with eggs, which come out not through the Müllerian canals (they are reduced), but through short tubes coming from the gonads and opening outward with an independent opening or into the common urogenital opening. Consequently, mature eggs do not enter the body cavity, but quickly exit the body of the female. Fertilization in the vast majority of bony fish species is external. Internal fertilization, as well as viviparity, is characteristic of relatively few representatives of this class. The eggs are spawned on aquatic plants and, less frequently, on other underwater substrates, and in a minority of species, in the water column. Due to external fertilization, a mass of gametes, zygotes and fry die. Therefore, the fertility of bony fish is very high. For example, carp produces more than 1 million eggs, pike - about 1 million, halibut - 2-3.5 million, cod - up to 1 million. The maturation of the gonads depends on various factors - internal and external. Pituitary hormones have an accelerating effect on the maturation of the gonads.
Fertilization of eggs can be done under artificial conditions by mixing eggs and fish seed in the presence of a small amount of water. Currently, this technique is well developed and is successfully used on a large scale in so-called fish hatcheries. Fertilized eggs develop in favorable conditions, usually to the stage of fry, capable of obtaining food in natural reservoirs where they are released. Such measures contribute to the restoration of valuable commercial fish, the number of which has sharply decreased due to pollution of water bodies, difficulty in migrating fish to their breeding grounds, and their increased fishing.
The growth rate of fish is influenced by various living conditions: nutrition, temperature, composition of substances dissolved in water, etc. Growth, depending on changes in living conditions, is uneven. It is known, for example, that it slows down in cold weather, which can be seen in the annual rings of fish scales. Studies of fish growth in different water bodies are of great theoretical and practical importance, since thanks to them it is possible to find out what conditions favor it, what conditions, on the contrary, delay it, how stocks of commercial fish are restored, etc.
The lifespan of fish is different: some live less than a year (some types of anchovy, etc.), others - several years (Pacific salmon - chum salmon, pink salmon, etc.), others - several dozen years and even about 100 years (large sturgeon, pike, carp, etc.).
Fish-like creatures (jawless and fish) have adaptations (that arose over a long period of evolution) for moving in water, obtaining food, saving from predators, etc.
Based on these adaptations, they developed regular movements characteristic of different periods of their life - migration. The shortest and most frequent of them are daily migrations. They depend on the time of day. Longer seasonal migrations depend on the season of the year. These, in particular, include wintering migrations, when fish go to depth and, in a sedentary state, without feeding, wait out the unfavorable season for them. For example, anchovy, which feeds and breeds in the Sea of Azov, winters in the Black Sea, since the water there is not subject to such strong cooling as in the shallow Sea of Azov.
Many fish make long, long-distance migrations in some species, called feeding migrations, to places where there are sufficient quantities of the organisms on which they feed. For example, after the end of the breeding season in the Atlantic Ocean, cod migrates to the Barents Sea and some other northern seas.
Spawning migrations are widespread among fish, ensuring their reproduction, sometimes in very distant places from the areas where they live, feed and grow for a long time. These species include migratory fish that live in the seas, but breed in rivers flowing into these seas. Thus, very valuable sturgeon fish (sturgeon, stellate sturgeon, beluga, etc.) live in the Caspian, Azov and Black seas before the onset of the breeding season, and for spawning they go to the upper reaches of rivers flowing into these seas. After this, they return to the seas, where they live until the next breeding season. The fry, which develop from eggs laid and fertilized in rivers, are carried by the current to the seas, where they grow for a long time.
Such fish reproduce several times during their life. But there are fish that live for several years in the oceans and seas, but reproduce only once in their lives. These include Pacific salmon (chum salmon, pink salmon, Chinook salmon, etc.), which for reproduction go to the Far Eastern rivers of Russia, the rivers of North America, Japan, Korea, China, in which they spawn. During spawning migrations, fish, as a rule, do not feed and die as a result. Unlike the mentioned fish, the freshwater eel, which lives for a long time (up to 20 years or more) in the rivers of Europe, never reproduces there, but makes long migrations (7000-8000 km) to the Sargasso Sea, where it spawns and then dies. The eel fry are picked up by the Gulf Stream and after 2 years they reach the shores of Europe and then enter the rivers.
There is also a group of semi-anadromous fish that live in desalinated parts of the seas and reproduce in the lower reaches of rivers flowing into these seas. These include populations of roach, carp, and bream living in the north of the Caspian Sea.
Migrations are also known in many invertebrate animals that have fairly efficient methods of movement. In vertebrates they are the most complex and prolonged due to the high development of their nervous, motor and other organ systems. Migrations are carried out by hereditarily fixed instincts, developed as a result of long-term natural selection. Thanks to migrations, animals comprehensively use different parts of their habitats. Migration studies are of great importance for nature conservation and the appropriate use of commercial animal species.
Practical significance of fish. Bony fish are sources of protein and a number of other substances necessary for adequate human nutrition. World population during the 20th century. and especially in recent decades has increased greatly. In this regard, the production of fish (as well as aquatic mollusks, crustaceans and other invertebrates) increased sharply. In pre-revolutionary Russia, fish was caught mainly in rivers, other freshwater bodies and in the southern seas of the country.
The development of pond fish farming plays a significant role in increasing fish production. In ponds, fish feed on insect larvae (mainly chironomid larvae), crustaceans, worms, etc. In order to increase the fish productivity of ponds, fish are fed with cakes, legumes, etc. Most often, various races of carp are grown in ponds. Together with carp, crucian carp, tench and other species of fish that are not competitors in nutrition can be bred in ponds. In properly organized pond farms, there are several types of reservoirs (for breeding, raising fry, feeding commercial fish, wintering, etc.). In such farms you can get 15-20 centners of fish or more from 1 hectare. Pond fish farming is one of the profitable branches of livestock farming.
Systematic review
Currently existing bony fish belong to two subclasses - ray-finned and lobe-finned fish.
