The external and internal structure of the fish. §21

Bony fishes are the most numerous superorder of bony fishes. It owns 90% of modern fish. They are found in all oceans and seas, and in fresh water bodies of all continents. In appearance, they are diverse, which is associated with a variety of living conditions and lifestyles.

Skin. The body is covered with bony scales. Scales (if any) are always bony: cycloid or ctenoid. The location of the scales is tiled; caudal fin homocercal.

Skeleton. The spine is represented by amphicoelous vertebrae, divided into the trunk and tail sections. Bone skull. The skeleton of the pectoral fins has no basals and consists only of radials and skin rays; the pelvic fin skeleton consists only of skin rays.

There is no spiral valve of the bowel.

swim bladder performs a hydrostatic function, which is caused by a change in the volume of gases in the bubble and which leads to a change in the density of the fish.

Respiratory system. There are 4 complete gills, gill covers, and on the inside of which there is a row of rudimentary petals - false gills.

Circulatory organs. Most do not have an arterial cone, the abdominal aorta at the beginning has a swelling - an arterial bulb. The number of afferent and efferent branchial arteries is 4.

Nervous system and sense organs. The brain has a more primitive structure than that of cartilage. The forebrain is small, the midbrain and cerebellum are relatively large. Eyes - the lens is round, the cornea is flat. The organ of hearing is represented only by the inner ear. Taste organs are represented by taste buds. Lateral line - a channel running in the skin along the sides of the body.

excretory organs represented by long mesonephric buds.

Reproductive organs represented by paired testes and ovaries.

Bony fish - Teleostei (about 20 thousand living species) are united by 8-10 superorders, including 30-40 orders:

Detachment Clupeiformes - Herrings (herring, anchovies)

Detachment Salmoniformes– Salmon-like (trout, grayling, chum salmon)

Order Anguilliformes - Eels

Order Cypriniformcs - Carps (minnow, bream, carp, crucian carp)

Order Gadiformes - codfish (cod, pollack, haddock, navaga)

Order Gasterosteiformes - Sticklebacks

Order Mugiliformes - Mullets

Order Perciformes - Perciformes (Tunas, horse mackerels, sailboats, swordfish).

Detachment Pleuronectiformes - Flatfishes, etc.

26. Subclass Lobe-finned, or Choano-breathing fish - Sarcopterygii. Features of progressive and primitive organization.

Scales cosmoid or bony. Throughout life, preserving the notochord, surrounded by a dense connective tissue fibrous-elastic membrane. The upper and lower arches develop, and sometimes there are underdeveloped vertebral bodies in the caudal region. Among the integumentary bones or diphycercal. Paired fins with scaled fleshy lobe at the base. There is an arterial cone in the heart. The intestine has a spiral valve and opens into the cloaca. As outgrowths of the abdominal side of the initial part of the esophagus, one or two bubbles are formed that perform the function of the lungs. Known from the Lower Devonian.

27. Superorder Cross-finned fish -Crosopterygii as the oldest, almost completely extinct group of fish. Features of the structure and geographical distribution. Significance of lobe-finned fish for understanding the origin of extraterrestrial vertebrates.

Modern crossopterygi are coelacanths (coelocanths). Body length - 125-180 cm.

Predators. There is a degenerated lung in the body cavity. The brain skull is divided into two parts - the olfactory and the brain proper, movably connected to each other. The degree of ossification of the skull varies, integumentary ossifications are developed. There are no internal nostrils, they are capable of breathing atmospheric air. The coelocanths represent the branch of fish from which the amphibians originated. They are characterized by double breathing.

At the base of the fins there is a blade, inside which is the skeleton of the main part of the fin. Thus, the musculature of the limb is located, as in terrestrial vertebrates. The fin skeleton is elongated and resembles a five-fingered limb.

The body is covered with cosmoid scales - bone plates covered with cosmin (modified dentin) and a layer of enamel.

There are sprinklers.

They originally lived in fresh water, in which, probably, there was a lack of oxygen from time to time. In this regard, double breathing developed: with a lack of oxygen, the fish rose to the surface of the water and swallowed air. The clogging of reservoirs with growing and dead vegetation was, apparently, a prerequisite for the development of peculiar paired limbs, which, with the presence of muscles, could be used for rowing, support on a solid substrate. And this became a prerequisite for the transformation of fins into five-fingered limbs. Having arisen in fresh water bodies, lobe-finned fish subsequently switched to life in the sea.

Ecology of fish. The specificity of the aquatic environment and the living conditions of fish in the water. Fish migrations and their causes. Objects of food and methods of foraging. Reproduction and timing. Growth and age of the fish. Sexual dimorphism. Fertility. Caring for offspring.

Water as a living environment has a number of specific features that create unique conditions for existence. The mobility of water ensures to a large extent the passivity of the movement of fish and their food objects.

Temperature fluctuations are less than in the ground-air environment. The ability of water to dissolve gases, in particular oxygen, is inversely proportional to its temperature and salinity. The need for oxygen in fish increases as the water temperature rises.

Migrations. At all stages of life, fish need different environmental conditions. The conditions necessary for spawning are different from those suitable for wintering, etc. This leads to a search for conditions suitable for each life stage.

The spawning migrations of anadromous fish are the most complex and diverse; they are associated with the transition from seas to rivers (anadromous migrations) (salmon, sturgeon, herring, cyprinids) or, conversely, from rivers to seas (catadromous migrations) (eels). Semi-anadromous fish live in the pre-estuary desalinated parts of the seas, and for breeding they enter rivers (vobla, bream, carp, catfish).

Nutrition. The nature of food in fish is extremely diverse. Fish feed on almost all living creatures that live in the water: from the smallest planktonic plant and animal organisms to large vertebrates. The nature of food varies depending on the conditions of the reservoir, the time of year and the age of the fish. The nature of the food is varied. They feed on all living things that live in the water. Adaptation to the type of food is seen in the structure of the teeth and the structure of the oral apparatus. Methods for obtaining food are varied. In connection with the nature of nutrition, the structure of the oral apparatus in fish is different. In carnivores, the mouth is armed with sharp, recurved teeth that sit on the jaws; stingrays have teeth in the form of wide plates. Some fish have pharyngeal teeth that sit on the inner edges of the gill arches.

Reproduction. The vast majority of fish are dioecious. High fertility. Fish do not have a specific breeding season. Three groups of fish are distinguished according to spawning time: 1. Spawning in spring and early summer - sturgeon, carp, catfish, herring, pike, perch. 2. Spawners in autumn and winter - Atlantic salmon, river trout. 3. There is definitely no breeding juice - chum salmon, salmon.

Caring for offspring. The conditions in which the eggs are located after fertilization are different. Most fish do not express concern for offspring. Some place it in special facilities and guard it. Some fish carry eggs on their bodies or inside their bodies. American sea catfish hatch eggs in the mouth.

The last degree of complication of the process of reproduction in fish is expressed in live birth. To the greatest extent it is characteristic of cartilaginous fish. Among bony fish, this phenomenon is rare.

Height and age. The lifespan of fish is different. There are species that live more than a year: some gobies, anchovies. Beluga up to 100 years old. Some flounders are 50 years old. In fishing conditions, life expectancy decreases. The seasonal periodicity of growth is expressed. Age determination is made by scales and parts of the skeleton.

The class Bony fish includes the vast majority (more than 20,000) species of the entire superclass Pisces. Bony fish are common in a wide variety of water bodies. The variety of living conditions determines the richness of this group of species and their extreme diversity.

The class Osteichtyes includes all bony fishes; scales - cycloid or ctenoid, depending on the shape - smooth or serrated, respectively. In terms of the number of species and the variety of forms, bony fish are far superior to cartilaginous ones. Probably the most advanced is the Teleostei (bony fish) order, which includes herring, trout, salmon, carp, eel, flying fish, etc.

The main general features of the class are as follows.

The skeleton is always more or less bony. The bone skeleton arises in two ways. The initial type of ossification is the so-called skin, or integumentary, bones. Embryonally, they arise in the connective tissue layer of the skin, regardless of the cartilaginous elements of the skeleton, to which they are only adjacent. In connection with the indicated features of development, the integumentary bones, as a rule, have the form of plates. In addition to the integumentary bones in the skeleton of fish, there are chondral, or cartilaginous, bones. Embryonally, they arise as a result of the successive replacement of cartilage by bone substance, which is produced by osteoblasts. Histologically formed chondral bones do not differ significantly from integumentary bones. The ossification of the skeleton, which occurs through the appearance of chondral bones, does not introduce significant changes in the overall structure of the skeleton. The formation of integumentary ossification leads to the appearance of new elements of the skeleton, and, consequently, to its general complication.

The intergill septa in the respiratory apparatus are reduced, and the gill filaments sit directly on the gill arches. There is always a bony gill cover covering the gill apparatus from the outside.

The vast majority of species have a swim bladder.

In the vast majority of bony fish, fertilization is external, the eggs are small, devoid of horn-shaped membranes. Live birth occurs in an insignificant number of species. The classification of bony fish is extremely difficult; at present, there are several views on the taxonomy of this group. We take one of them as a basis and distinguish two subclasses:

1) Subclass Ray-finned fish (Actinopterygii) 2) Subclass Lobe-finned fish (Sarcopterygii).

17. External and internal structure of bony fish. External structure

Body sizes range from 1 cm (Philippine goby) to 17 m (herring king); blue marlin weighs up to 900 kg. The body shape is usually elongated and streamlined, although some bony fish are flattened in the dorsal-ventral direction or laterally, or vice versa are spherical. The translational movement in the water is carried out due to the wave-like movements of the body. Some fish at the same time "help" themselves with a caudal fin. Paired lateral, as well as dorsal and anal fins serve as stabilizer rudders. In some fish, individual fins have been transformed into suckers or copulatory organs. Outside, the body of bony fish is covered with scales: placoid (teeth laid “in the parquet”), ganoid (rhombic plates with a spike), cycloid (thin plates with a smooth edge) or ctenoid (plates with spines), periodically changing as the animal grows. Annual rings on it allow you to judge the age of the fish. Various types of scales Many fish have well-developed mucous glands on the skin, their secretions reduce the resistance to the oncoming flow of water. In some deep-sea fish, luminous organs develop on the skin, which serve to identify their species, consolidate the flock, lure prey, and scare away predators. The most complex of these organs are similar to a searchlight: they have luminous elements (such as phosphorescent bacteria), a mirror reflector, a diaphragm or lens, and an insulating black or red coating. The color of the fish is very diverse. Usually, fish have a bluish or greenish back (the color of the water) and silvery sides and belly (hardly visible against the background of a light "sky"). Many camouflage fish are covered with stripes and spots. The inhabitants of coral reefs, on the contrary, amaze with a riot of colors.

According to the latest scientific data, the ancestors of modern fish - jawless animals that resemble them in appearance - lived already in the early Cambrian, about 530 million years ago. It is conceivable that such creatures, found in 1999 in Yunnan Province, may be the progenitors of all vertebrates.

At the moment, cartilaginous fish, bone fish (lobe-finned and ray-finned) make up more than half of all living on the planet. In total, there are about 31 thousand species of a wide variety of shapes and sizes that live in salt and fresh water. The study of ancient creatures is engaged in a separate science - ichthyology. Let us dwell in more detail on the classes, their features and differences.

cartilaginous fish

The main feature of all representatives of the class is that their skeleton consists of cartilage, which over time, as a result of the deposition of minerals, can become quite hard. Previously, for this reason, they were considered prehistoric animals. However, many of them are characterized by live birth, sometimes even with the formation of a bile placenta - this is how cartilaginous fish differ radically from bone fish.

In addition, they have several more anatomical structural features. First, the absence of a swim bladder. Therefore, they have to move in order to sink to the bottom of the reservoir. Secondly, cartilaginous fish lack gill covers, and the gills open outwards with characteristic slits. Thirdly, they are all covered which is similar to the teeth of vertebrates. It consists of dentin and a layer of enamel covering it. Such scales are not restored when lost, however, with the growth of the fish, its number increases.

Life support systems in cartilaginous fish

The characterization of cartilaginous and bony fish will not be complete if we do not mention the main systems: circulatory, digestive and sexual, in which differences are observed. Cartilaginous have red blood (due to the presence of hemoglobin and red blood cells), which is produced by the spleen. The circulatory system itself in structure resembles that of cyclostomes. Kidneys stretch along the spine in the form of two dark red stripes. The intestines of cartilaginous fish consists of three sections, these are: the large and small intestines, and the rectum. The liver and pancreas are well developed. But the most important thing is that the classes Cartilaginous fish and Bony fish differ in the structure of the reproductive system. The first is characterized by the formation of an egg, which can be laid in the external environment or remain in the lower part of the oviduct. In the second case, the embryo begins to develop in the mother's body.

Classification of cartilaginous fish

All of the currently existing representatives of the class Cartilaginous fish are divided into three superorders.

Bony fish: general characteristics

For a long time, until the 21st century, cartilaginous fish, bony fish were considered as two classes. However, in the scientific community, a different point of view is becoming more widespread. So, the Canadian zoologist in his works defines lobe-finned and ray-finned fish in separate classes, and bone ones, respectively, in a superclass. These are the most diverse inhabitants of all types of reservoirs. Their mouth is formed by grasping jaws and teeth located on them, the gills are located on and the nostrils are paired.

Differences from cartilaginous fish

The most important difference between bony fish and cartilaginous fish is clear from the name - the skeleton. He's made of bones. In the internal cavity are located the circulatory, excretion, reproduction and digestion systems. The scales are also characteristic, one of three types: cycloid, ctenoid or ganoid.

The next difference is the presence located under the spine and filled with gases that secrete blood vessels. With an increase in its volume, the fish easily floats to the surface, with a decrease, it goes into the depths.

Differences have not only external signs of cartilaginous and bony fish, but also reproductive organs, as already mentioned. Most representatives of the second group are characterized by external fertilization occurring in the aquatic environment. This process is called spawning, it occurs at a certain time and is accompanied by characteristic behavior.

ray-finned fish

This is the numerically predominant class in the modern diversity of fish, there are more than 20 thousand species, which is about 95%. They inhabit all corners of the planet, from the Arctic seas to the hot equator, their sizes range from 8 mm to 11 meters, and the weight of individual individuals reaches more than two tons. The name, as you might guess, is associated with the structure of paired fins, in which there is no basal axis. The class, in turn, is divided into two groups: New-finned (the most prosperous species) and Bone-cartilaginous fish. The structure of the latter has distinctive features. They have a swim bladder, but at the same time, their skeleton mainly consists of a chord, it has only cartilaginous arches and is not dissected, there are no vertebral bodies as such. A distinctive feature is the rostrum and lower mouth. Many of them are commercial, in particular sturgeon (in the photo below - the catch of the beluga).

lobe-finned fish

A small class of fish whose skeleton is based on an elastic chord. They combine progressive and archaic features, all representatives belong to two modern superorders - the Crossopterygians and the Lungfishes. Both groups combine ancient fish. Lungfish live in fresh water bodies of Australia, South America and Africa. They have not only gills, but also lungs. This allows them to do without water for some time and feel free in oxygen-depleted water bodies. In total, 6 species are known: four African protopters (photo below), the Australian horned tooth and the South American flake.

Superorder Crossoptera

It is considered nearly extinct. Only one genus has survived to this day - Latimeria (pictured below), numbering two species. Moreover, both of them were discovered relatively recently, the first copy was caught in the Indian Ocean in 1938. It is believed that lobe-finned fish are inhabitants of fresh water bodies in which there was a lack of oxygen. In this regard, they developed musculature at the base of the fins and a dual mode of breathing (lungs and gills). This allowed some subsequently to move back to the seas, and freshwater eventually died out. There is an assumption that it was the lobe-finned fish that gave rise to the class Amphibians.

Thus, cartilaginous fish, bone fish have a number of individual characteristics. The main ones are observed in the structure of the skeleton (cartilaginous or bone), the presence or absence of a swim bladder, the type of scales, the reproductive system and the method of reproduction.

Representative of bony fish - perch (Perea fluviatilis)

External structure. The body of the perch is fusiform, somewhat laterally compressed. The pointed head imperceptibly passes into the body, and the latter, gradually narrowing, passes into the tail section, the anus is considered the anterior border of which. Immediately behind the anus, the genital opening opens on the urogenital papilla, and behind it the urinary opening. The pectoral fins, like all fish, are attached from the sides of the body immediately behind the gill openings, and the ventral fins are on the ventral side, and in the perch they are moved far forward and are located under the pectoral fins. Unpaired fins are represented by two dorsal fins, caudal and anal. Unlike the shark, all fins are supported by bony rays. Some of them are soft segmented (for example, the rays of the posterior dorsal and caudal fins), others are hard, non-segmented (for example, the rays of the anterior dorsal fin). In addition, unlike the shark, the paired fins are located not in the horizontal, but in the vertical plane, and the caudal fin is equally lobed. However, its internal structure is such that the axial skeleton at the base of the fin turns up. This type of caudal fin, which has an externally symmetrical and internally asymmetric structure, butsits the name of homocercal. The mouth is located at the end of the head and is bordered by bony jaws. Round eyes are devoid of eyelids. Anterior to the eyes on the dorsal side of the head are paired nostrils, with each nostril subdivided by a transverse leathery bridge into two parts: anterior and posterior. Behind the sides of the head are wide flat gill covers (operculum), under which the gills are located. Below the operculum are rays that support the gill membrane.

. I - ctenoid (perch); II - cycloid (carp fish): a - annual rings

The role of fins in swimming. Various movements of a swimming fish are made with the help of various fins. The caudal fin, together with the entire caudal section, serves as the main organ for the translational movement of the body, and also plays the role of a rudder. With the help of paired fins, the fish makes a turn. In addition, they serveto hold the body in its natural position; if they are cut off, then the fish floats helplessly belly up. The dorsal and ventral fins do not participate in active movement, but contribute to it, giving the body a certain stability.

Skin. The entire body of the perch, with the exception of the head, is covered with numerous bony scales, which overlap each other like tiles and are arranged in regular rows. Each scale is a more or less rounded thin plate, the main part of which is immersed in the skin, and the outer edge is covered with small teeth.chikami. Such scales are called ctenoid, in contrast to cycloid scales, which have a smooth, toothless outer edge (for example, scales of carp, roach, crucian carp). Along the entire body, from the head to the root of the caudal fin, an arched curved lateral line (linea lateralis) stretches, formed by a series of holes that pierce the scales. Numerous unicellular skin glands, like those of sharks and lampreys, secrete abundant mucus, which plays the role of a lubricant that weakens the friction of the body of the fish against the water when swimming.

1. Features of the external structure of bony fish on the example of river perch.

Fish are ancient primary aquatic vertebrates. Unlike non-cranial, they lead an active lifestyle. Features of their structure are associated with the aquatic environment. More than 20 thousand species of fish are known, which are combined into two classes: Cartilaginous and Bone. The most numerous and diverse are bony fish, more than 90% of which are a group of bony fish. These include herring-like, cod, carp-like, salmon-like, perch-like, pike-like, etc.

A typical representative is river perch. The shape of the body is streamlined, the head smoothly passes into the body, and the body into the tail. On the head is a mouth with lips, large eyes, nostrils and gill covers. There are fins: paired (pectoral and ventral) and unpaired - caudal, dorsal and anal. The skin is covered with bony scales. Scales lean on each other in a tiled manner. The skin glands secrete mucus that covers the scales and reduces the friction of the body against the water.

2. Features of the internal structure of bony fish on the example of river perch.material from the site

The skeleton of a river perch consists of a large number of bones. It distinguishes the skull, spine, skeleton of the shoulder and pelvic girdle, the skeleton of the fins. The skull consists of the braincase, jaw bones, gill arches and gill covers. The spine consists of the trunk and tail vertebrae. Ribs are attached to the trunk vertebrae. The digestive system includes a mouth with teeth, pharynx, esophagus, stomach, small intestine, where the ducts of the gallbladder, liver and pancreas open, the posterior intestine, anus. There is a swim bladder (an outgrowth of the anterior intestine), filled with a mixture of gases. It participates in gas exchange and is a hydrostatic organ. Fish breathe with gills, which consist of gill arches and gill filaments pierced by blood vessels. Perch have four pairs. The circulatory system is characterized by a two-chambered heart and one circle of blood circulation. Venous blood flows through the heart, which becomes arterial in the gills. The excretory system includes long trunk kidneys, ureters and bladder. The nervous system consists of the brain and spinal cord and nerves extending from them. The brain is protected by the bones of the cranium and consists of five sections: the medulla oblongata, the cerebellum, the midbrain, the intermediate section, and the small hemispheres of the forebrain with olfactory lobes. The organs of vision are the eyes, they have a flat cornea and a large crystal face. Eyelids are absent. The organs of smell in the nasal cavity, the organ of hearing - the inner ear, the organ of taste - in the oral cavity and on the lips. A well-marked lateral line stretches along the body - an organ that perceives the direction and strength of the flow of water, as well as sound vibrations. Tactile cells are scattered throughout the body. Bony fish are dioecious animals. Reproductive organs: paired testicles and ovaries, genital ducts. Fertilization is external. Development occurs with transformation (larva - fry - adult fish).