Features of the structure of the internal organs of fish. Internal organs of fish. Fish brain

127. Draw a diagram of the external structure of the fish. Label its main parts.

128. List the structural features of fish associated with an aquatic lifestyle.
1) Streamlined torpedo-shaped body, flattened in the lateral or dorsal-abdominal (in benthic fish) directions. The skull is motionlessly connected to the spine, which has only two sections - the trunk and the caudal.
2) Bony fish have a special hydrostatic organ - a swim bladder. As a result of changes in its volume, the buoyancy of the fish changes.
In cartilaginous fish, body buoyancy is achieved by the accumulation of fat reserves in the liver, and less often in other organs.
3) The skin is covered with placoid or bony scales, rich in glands that abundantly secrete mucus, which reduces friction of the body with water and performs a protective function.
4) Respiratory organs - gills.
5) Two-chamber heart (with venous blood), consisting of an atrium and a ventricle; one circle of blood circulation. Organs and tissues are supplied with arterial blood rich in oxygen. The life activity of fish depends on water temperature.
6) Body buds.
7) The sensory organs of fish are adapted to function in the aquatic environment. The flat cornea and almost spherical lens allow fish to see only close objects. The sense of smell is well developed, allowing it to stay in a flock and detect food. The organ of hearing and balance is represented only by the inner ear. The lateral line organ allows one to navigate water currents, perceive the approach or distance of a predator, prey or school partner, and avoid collisions with underwater objects.
8) For the majority - external fertilization.

129. Fill out the table.

Fish organ systems.

130. Look at the drawing. Write the names of the sections of the fish skeleton indicated by numbers.

1) skull bones
2) spine
3) rays of the caudal fin
4) ribs
5) rays of the pectoral fin
6) gill cover

131. In the drawing, use colored pencils to color the organs of the fish’s digestive system and write their names.

132. Draw and label the parts of the circulatory system of a fish. What is the significance of the circulatory system?

The circulatory system of fish ensures the movement of blood, which delivers oxygen and nutrients to the organs and removes metabolic products from them.

133. Study the table “Superclass Pisces. The structure of the perch." Look at the drawing. Write the names of the internal organs of the fish, indicated by numbers.

1) kidney
2) swim bladder
3) bladder
4) ovary
5) intestines
6) stomach
7) liver
8) heart
9) gills.

134. Look at the drawing. Write the names of the parts of the fish's brain and parts of the nervous system indicated by numbers.

1) brain
2) spinal cord
3) nerve
4) forebrain
5) midbrain
6) cerebellum
7) medulla oblongata

135. Explain how the structure and location of the nervous system of fish differs from the nervous system of hydra and beetle.
Fish have a much more developed nervous system than hydra and beetle. There is a spinal and cephalic brain, consisting of sections. The spinal cord is located in the spine. Hydra has a diffuse nervous system, that is, it consists of cells scattered in the upper layer of the body. The beetle has a ventral nerve cord, with an expanded ologopharyngeal ring and a suprapharyngeal ganglion at the head end of the body, but there is no brain as such.

136. Complete laboratory work “External structure of fish.”
1. Consider the features of the external structure of the fish. Describe the shape of its body, the color of its back and abdomen.
The fish has a streamlined, oblong body shape. The color of the abdomen is silver, the back is darker.
2. Draw a drawing of the fish’s body and label its sections.
See question #127.
3. Examine the fins. How are they located? How many are there? Label the names of the fins in the picture.
The fish has paired fins: ventral, anal, pectoral and unpaired: caudal and dorsal.
4. Examine the fish's head. What sense organs are located on it?
On the head of the fish there are eyes, taste buds in the mouth and on the surface of the skin, and nostrils. In the head section there are 2 openings of the inner ear; at the border between the head and the body there are gill covers.
5. Examine the scales of the fish under a magnifying glass. Calculate the annual growth lines and determine the age of the fish.
The scales are bony, translucent, covered with mucus. The number of lines on the scales corresponds to the age of the fish.
6. Write down the features of the external structure of the fish associated with the aquatic lifestyle.
see question No. 128

Pisces class- this is the largest group of modern vertebrates, which unites more than 25 thousand species. Fish are inhabitants of the aquatic environment; they breathe through gills and move with the help of fins. Fish are distributed in different parts of the planet: from high mountain reservoirs to ocean depths, from polar waters to equatorial ones. These animals inhabit the salty waters of the seas and are found in brackish lagoons and the mouths of large rivers. They live in freshwater rivers, streams, lakes and swamps.

External structure of fish

The main elements of the external body structure of a fish are: head, operculum, pectoral fin, ventral fin, body, dorsal fins, lateral line, caudal fin, tail and anal fin, this can be seen in the figure below.

Internal structure of fish

Fish organ systems
	1. Skull (consists of the braincase, jaws, gill arches and gill covers) 2. Skeleton of the body (consists of vertebrae with arches and ribs) 3. Skeleton of fins (paired - pectoral and abdominal, unpaired - dorsal, anal, caudal)	1. Brain protection, food capture, gill protection 2. Protection of internal organs 3. Movement, maintaining balance
Musculature	Wide muscle bands divided into segments	Movement
Nervous system	1. Brain (divisions - forebrain, middle, medulla oblongata, cerebellum) 2. Spinal cord (along the spine)	1. Movement control, unconditioned and conditioned reflexes 2. Implementation of the simplest reflexes, conduction of nerve impulses 3. Perception and conduction of signals
Sense organs	3. Hearing organ 4. Touch and taste cells (on the body) 5. Lateral line	2. Smell 4. Touch, taste 5. Feeling the direction and strength of the current, the depth of immersion
Digestive system	1. Digestive tract (mouth, pharynx, esophagus, stomach, intestines, anus) 2. Digestive glands (pancreas, liver)	1. Capturing, chopping, moving food 2. secretion of juices that promote food digestion
swim bladder	Filled with a mixture of gases	Adjusts immersion depth
Respiratory system	Gill filaments and gill arches	Carry out gas exchange
Circulatory system (closed)	Heart (two-chambered) Arteries Capillaries	Supplying all body cells with oxygen and nutrients, removing waste products
Excretory system	Kidneys (two), ureters, bladder	Isolation of decomposition products
Reproduction system	Females have two ovaries and oviducts; In males: testes (two) and vas deferens

Topic 6. ANATOMICAL FEATURES OF CARTILAGE GANOIDS (CARTILAGE-BONEY FISHES)

Material and equipment. A representative of the sturgeon family and skeletal elements of sturgeons fixed in formalin (alcohol) and opened (one for 2-3 students).

Tables: General location of internal organs, digestive system, circulatory system; Genitourinary system of male and female; Brain; Skeleton.

Dissecting tools: tweezers, dissecting needle, stationery pins (one set for 2-3 students).

Paraffin baths (one for 2-3 students).

Introductory remarks. Cartilaginous ganoids (order Acipenseriformes) retain a number of primitive features in their structure. Externally, this can be seen in the structure: rostrum and squirter; paired fins horizontally located in relation to the body; heterocercal caudal fin; the anus, which is located near the ventral fins. Of the internal organs, a primitive structure can be observed in: the cartilaginous axial skull; the jaw arch, represented by the palatoquadrate and Meckel's cartilages; conus arteriosus in the heart and spiral valve in the intestine. These features bring cartilaginous ganoids closer to elasmobranchs (Elasmobranchii).

At the same time, they have characteristics that make them classified as bony fish. The skeleton of cartilaginous fish contains ossifications of the integumentary bones of the skull and vomer; parasphenoid and secondary jaws; operculum; collarbone

The combination of cartilaginous and bone elements in the skeleton determined the first name of these fish - cartilaginous. The presence of remains of ganoid scales and fulcra on the upper lobe of the tail (evidence of antiquity of origin) determined the second name - cartilaginous ganoids.

Exercise. Considering the difficulty of obtaining material, the lesson is carried out on an opened fixed fish of the Sturgeon family. The main attention is paid to the topography of the internal organs. From organ systems, organs that are accessible to the naked eye and do not require dissection are considered. A detailed introduction to the anatomy of this group of fish is given in the lecture course. When performing work, it is necessary to consider the external and internal structure of the fish

When studying the external structure, you need to pay attention to the shape of the body, snout, antennae, position and character of the mouth, nasal openings, eyes, gill cover and gill membranes, squirts, fins, type of caudal fin, bony bugs and ganoid scales; anal and genital openings

When studying the internal structure, you need to pay attention to the location of the internal organs.

Digestive system: oral cavity; pharynx; esophagus; stomach; mid and hindgut; spiral valve; liver; gallbladder; pancreas; pyloric gland

Respiratory organs: gill cover; gill slits; gill arches; gill filaments and stamens.

Cardiovascular system: heart (atrium and ventricle); venous sinus, conus arteriosus; spleen.

Genitourinary system: kidneys; ureters; ovaries; oviducts; testes; vas deferens.

Nervous system and sensory organs: forebrain with olfactory lobes; diencephalon, midbrain; cerebellum, medulla oblongata; lymphoid organ, organs of touch; sense of smell; vision and lateral line.

On finished preparations and drawings, you need to examine the skeleton of the head (cerebral and visceral); axial skeleton, skeleton of paired fins and their belts; skeleton of unpaired fins.

External building. Sturgeons have a torpedo-shaped body. Like all fish, it is divided into the head, body and tail. The head has the shape of a cone. Snout shape(rostrum) can be conical, blunt, pointed, xiphoid, rounded or spatulate. This is a species characteristic. On the underside of the snout in front of the mouth there are two pairs of antennae, or tentacles(ciri). Their shape varies among different species of sturgeon. In sterlet and thorn they are fringed, in stellate sturgeon they are without fringes, and in kaluga they are flattened laterally, without leaf-like appendages. Antennae are a species characteristic.

The mouth (stoma) of all sturgeons is lower. In representatives of the genus Acipenser it is in the form of a small transverse slit, and in belugas (genus Huso) it is a large semilunar one. The mouth is surrounded by fleshy lips in the form of ridges on the upper and lower jaws. It is retractable, and if you pull the upper jaw, the oral funnel extends along with the jaw apparatus. This has adaptive significance for the absorption of food from the bottom. On the sides of the head are located nasal openings, or nostrils(naris), behind them eyes(oculus).

The operculum covers the gill apparatus on the sides of the head. It is bordered by a gill membrane, which in sturgeons is attached to the intergill space isthmus, and in belugas it forms a free fold.

The spiraculum, in the form of a small pin hole, is located behind the eyes, on the upper edge of the gill cover. It is absent in shovelnoses and pseudoshovellings.

Five longitudinal rows run along the sturgeon's body bone bugs. One row is located on the back, two on the sides and two on the ventral side of the body. The number of bugs and their sizes are an important systematic feature. So, the sterlet has 57-71 side bugs, the Russian sturgeon has 24-50. Between the rows of bugs there are bone plates of various shapes and sizes. In the Siberian sturgeon, the plates between the dorsal and lateral bugs are small, star-shaped, while in the Russian sturgeon they are larger; in sterlet - in the form of sharp conical shields.

The pectoral fins are located behind the gill cover, almost horizontal to the body. The first ray of the fin has the appearance of a bony spine, the degree of development of which varies in different species. It is highly developed in the Atlantic and Amur sturgeon, and weakly in the Sakhalin sturgeon. The remaining rays of the fins (lepidotrichia) are bony and of dermal origin.

The pelvic fins are somewhat shifted back towards the caudal region, just like the pectoral fins, they consist of lepidotrichia.

The dorsal fin is carried back to the caudal fin and is located above the anal fin.

The anal fin is located behind the anus.

The caudal fin is heterocercal, epibate. Its upper blade is covered with ganoid scales, and along the upper edge of the blade there are fulcra.

The anal (anus) and genital (foramen genitale) openings are located between the ventral fins, one after the other.

Internal structure. On an opened fish, you can see the arrangement of organs in the body in their natural state (Fig. 23). To do this, place the fish in the bath on its side with the ventral side facing you and lift the flap of skin upward, attaching it to the paraffin with pins.

Figure 23 – General topography of the internal organs of the sterlet:

1 - heart; 2 - abdomen; 3 - liver; 4 – gallbladder; 5 6 7 – pyloric gland; 8 - duodenum; 9 – spiral valve; 10 – rectum; 11 – anus; 12 - pancreas; 13 – swim bladder; 14 – spleen; 15 – testes; 1 6 – genital duct; 17 - genital opening.

Internal organs are placed in the pericardial and abdominal cavities. The pericardial cavity lies closer to the head and is separated from the abdominal transverse septum. It contains heart(cor).

In the anterior abdominal cavity a multi-lobed liver(hepar), covering stomach(gaster) from the front and sides so that only its back is visible. Differentiated into sections departs from the stomach intestines. In its front part there is pyloric gland(glandula pyloriс) bean-shaped, to which is adjacent a Y-shaped large spleen (lien).

On the dorsal side of the body above the digestive tract lies swim bladder. It can be seen by retracting the anterior loop of intestine. In the depths of the abdominal cavity along the spine stretch oblong kidneys(ren). A significant part of the body cavity in adult fish is occupied by gonads.

Having examined the topography of the internal organs, we move on to a more detailed acquaintance with individual organs. Using tweezers and a dissecting needle, we consistently examine the internal structure of sturgeons.

Digestive system. The retractable, toothless (only larvae have teeth) mouth of sturgeon leads into oropharyngeal cavity(cavum oropharyngeus), consisting of an anterior - oral and posterior - gill cavities. Followed by esophagus(oesophagus) (Fig. 24), the beginning of which can be seen by turning away the stomach and liver. The esophagus passes into stomach(gaster), consisting of two sections: anterior - cardiac (gaster cardium) and posterior - pyloric (gaster pylorus). The pylorus leads to the midgut. Located at the border of the pyloric region and the beginning of the midgut pyloric gland(glandula pylorica). It is believed that it consists of numerous pyloric appendages connected by connective tissue and blood vessels into one organ, opening into the intestine with a wide opening.

Figure 24 – General view of the digestive organs of sterlet:

1 – esophagus; 2 – cardiac part of the stomach; 3 – pyloric part of the stomach; 4 – pyloric gland; 5 - duodenum; 6 – spiral intestine with a spiral valve; 7 – rectum; 8 - liver; 9 – gallbladder; 10 - pancreas; 11 – swim bladder; 12 – opening of the swim bladder; 13 – spleen.

Anterior midgut - duodenum(duodenum). In the posterior part of the midgut - spiral colon(colon) there is a spiral valve with 7-8 turns. It is formed by a rounded fold of the mucous membrane of the intestinal tube. Next is rectum(rectum), or short section ending anus(anus).

Of the digestive glands in the anterior part of the abdominal cavity there is a multilobular liver(hepar). In its anterior lobe is located gallbladder(vesica fellea), which opens through the bile duct into the duodenum at the base of the pyloric gland.

Pancreas(pancreas) is not always differentiated from the lobes of the liver, so it is often called hepatopancreas. In large sturgeons, the pancreas can be separate and located in the form of two longitudinal lobes at the junction of the pyloric stomach with the duodenum.

Respiratory system. The respiratory organs of cartilaginous ganoids, like those of other fish, are gills of ectodermal origin. The gill cavity is covered on the outside operculum. Under the operculum lie the gills. Each gill consists of gill arch(arcus branchialis), along the outer edge of which they are located in two rows gill filaments(fulum branchialis), separated from each other by gill septa. Unlike elasmobranchs, in which the gill septa extend to the edges of the gill openings, in cartilaginous ganoids they are reduced and do not reach the edge of the gill filaments.

From the inner side of the gill arches extend gill rakers, arranged, like the petals, in two rows. On the inner surface of the operculum you can see the opercular gill (branchia opercularis) - the semi-branch of the hyoid arch.

The cardiovascular system. On an opened representative of sturgeon you can see heart(cor), which is located in the pericardial cavity, is enclosed in the pericardial sac and consists of four sections. Anterior section - conus arteriosus(conus arteriosus) (Fig. 25), from which the abdominal aorta(aorta ventralis). The second part of the heart is thick-walled ventricle(ventriculus), the outer surface of which, like the surface of the arterial cone, is covered with vesicular extensions. This lymphoid gland, typical for sturgeon. Located under the ventricle atrium(atrium), communicating with the most posterior part of the heart - venous sinus(sinus venosus), having the appearance of a thin-walled sac.

Figure 25 – Sturgeon heart:

A– in section; b- side view; 1 – arterial cone; 2 – ventricle; 3 – atrium; 4 – venous sinus; 5 – lymphoid gland.

The hematopoietic organ visible on the dissected fish is spleen(lien) - a large organ that goes around the loop of the duodenum on the right and left and underlies it, which can be seen by lifting the intestine.

Genitourinary system. The genitourinary system of sturgeons retains the structural features of cartilaginous fish and bears new ones - bony ones. Like cartilaginous animals, they have oviducts with funnels opening into the body cavity (Fig. 26). They are similar to teleosts due to external fertilization, high fertility and the absence of a cloaca.

Figure 26 – Male genitals ( A) and females ( b) sterlet:

1 – testes; 2 – ovary; 3 – oviduct funnel; 4 – oviduct; 5 – vas deferens; 6 - urogenital canal.

Kidneys(ren) in the form of paired flat elongated bodies lie on the sides of the spine, merging behind the swim bladder. They are penetrated by blood vessels that form the renal portal system.

Ureters(ureter) and deferent ducts(vas deferens) serve as the primary renal ducts. Starting at the anterior edge of the kidney with separate tubules, they form a common duct. It is joined to it at the level of the posterior end of the swim bladder oviduct funnel, formed in sturgeon fish by the mesonephric canal. Through this funnel and the outlet channel, the whole liquid is discharged out.

Ovaries(ovarium) - paired gonads of the female - are located on the sides of the body cavity and attached to its dorsal wall by mesenteries. The excretory ducts of the ovaries are oviducts(oviductus), lying on the outside of the gonads in the form of wide tubes. They open into the body cavity with wide funnels at the level of the lower half of the gonad. The oviducts open externally through a common opening behind the anus.

Testes(testis) - paired sex glands of males - are also located on the sides of the body cavity. In contrast to the granular structure of the ovary, the testes have a lobular structure. They come from the testes seminiferous tubules(vas efferens), flowing into the upper part of the kidney.

Nervous system and sensory organs. Using a prepared specimen of the sturgeon brain and using tables, the general topography of the nervous system in the cranial region is examined. The brain of cartilaginous ganoids consists of five sections (Fig. 27).

Figure 27 – Sterlet brain:

A- view from above; b– bottom view; 1 – forebrain; 2 – diencephalon; 3 – pineal gland; 4 – funnel of the diencephalon; 5 – pituitary gland; 6 – midbrain; 7 – cerebellum; 8 - medulla; 9 - nerves.

Forebrain(telencephalon) small, not divided into hemispheres. Paired olfactory lobes extend from it in front, the posterior upper section is covered with a roof diencephalon(diencephalon). The pineal organ extends forward from the diencephalon on a peduncle, or pineal gland(epiphysis). At the bottom of the infundibulum of the lower part of the diencephalon is the inferior medullary gland, or pituitary(hypophysis). Behind the diencephalon is a poorly differentiated midbrain(mesencephalon) with the optic lobes, which are adjacent to the back cerebellum(cerebellum), which is a thickened anterior wall of the medulla oblongata and its rhomboid fossa. The last part of the brain is medulla(myelencephalon) passes into the dorsal. The roof of the medulla oblongata is covered on top by a pear-shaped lymphoid organ.

In different species of sturgeon, parts of the brain are developed differently, which is associated with their lifestyle and the activity of individual sense organs. The sterlet brain is characterized by a strong development of the olfactory sacs and olfactory nerves. Accordingly, the forebrain, where the olfactory centers are concentrated, is also significantly developed. The midbrain and cerebellum are well developed. The stellate sturgeon has a well-developed forebrain and diencephalon, while the optic lobes in the midbrain are less developed than the sterlet.

The main sense organs that allow sturgeon to navigate in the environment are the organs of the lateral line system and the organs of smell, while the organs of vision are poorly developed. The organs of the lateral line system are represented by canals and pits, or follicles. Side channel(canalis lateralis) runs in the lateral rows of beetles along the entire body. It opens to the surface through holes in the spaces between the bugs. On the head, the skin sensory organs are very complex and are represented by sensory channels, tubercles and pits (Fig. 28).

Figure 28 – Diagram of the location of the skin sensory organs of the lateral line on the head of a sterlet, etc.:

1 – sensory canals with neuromasts immersed in them; 2 – sensory tubercles; 3 – lateral line of the body; 4 - sensory fossae.

The sturgeon's olfactory organ, in the form of paired nasal openings, is located in front of the eyes. The olfactory sacs are well developed. On the outside, the olfactory sac is covered with a leathery film with two openings - the nostrils.

The organs of vision - the eyes - have a structure typical of fish.

The organs of touch are the antennae, on which taste buds are located.

Skeleton of fish. It is reviewed using medications and tables. The skeleton of sturgeon, like all fish, is divided into sections: the skeleton of the head, the body, the skeleton of paired fins and their belts, and unpaired fins.

Skeleton of the head. Like other fish, it is represented by two sections of the skull: axial (brainbox) and visceral (skeleton of the oral and gill apparatus) (Fig. 29).

Figure 29 – Cartilaginous skull of a sterlet:

A– cerebral; b– visceral; 1 – rostrum; 2 – olfactory department; 3 – orbital section; 4 – auditory department; 5 – occipital region; 6 – parasphenoid; 7 – pterygoid bone; 8 – maxillary-premaxillary bone; 9 – dentary bone; 10 – symplecticum; 11 – hyomandibular; 12 - skeleton of the gill apparatus.

Brain skull, or neurocranium, in sturgeons is completely cartilaginous; only in older fish does small ossification appear in it. It looks like a box in which several departments are distinguished.

Front of the skull - rostral section, or rostrum, is characterized by the presence of a highly developed unpaired conical shape of the rostral cartilage. Behind the base of the rostrum there are olfactory capsules - olfactory department(ethmoidal – pars ethmoidales). Behind it there are extensive recesses in the side walls of the skull - the orbit, or orbits(orbita), components orbital region(pars orbitalis). Goes for the eye sockets auditory, or temporal, department(pars otica, s. temporalis), the cartilaginous walls of which contain auditory capsules. The auditory section is short and passes into the occipital region, where the spine grows. At the base of the skull lies an unpaired integumentary ossification - parasphenoid(parasphenoideum), which in front abuts against unpaired vomer(vomer). In sturgeons, the base of the skull is wide; in the area of ​​the orbits the skull is expanded - the type of skull is platybasal.

The top of the skull is covered with a large number of dermal bones, forming a continuous shell with openings for the eyes and nostrils. In their development and structure, these skin bones are the same overgrown scales as the bugs located on the back and sides of sturgeons. Some of these bones in their location can be compared with the most permanent integumentary bones of the skull of higher fish (frontal - frontale; parietal - parietale, etc.).

The visceral skull (splanchnocranium) is represented in sturgeons by movable, dissected cartilaginous arches. Front arc – maxillary(arcus mandibularis) consists of the upper and lower jaws. They form a retractable mouth apparatus. The upper jaw is formed by a pair palatopterygoquadrate cartilage(cartilago palato-pterygoquardata). On the underside of the upper jaw lies integumentary pterygoid bone(pterygoideum). The anterior part of the maxilla is covered by the secondary maxilla - maxillopremaxillary bone(maxillo-praemaxillare). The lower jaw (mandibula) is represented Meckel's cartilage(cartilago Meckeli) and secondary jaws – integumentary dental bones(dentale). In old sturgeons, the inner side of Meckel's cartilage bears additional integumentary bones - lamellar(splenial) and corner(angulare).

Located behind the jaw arch sublingual, or hyoid, arch(arcus hyoideus). It consists of the upper section - hyomandibular cartilage(hyomandibulare), or pendant, and symplecticum(symplecticum). Part of the hyomandibular cartilage ossifies. Its lower end movably articulates with the symplecticum, and its anterior end articulates with the posterior end of the upper jaw. Thus, sturgeon fish have a clearly defined hyostyly.

Behind the hyoid arc there are five pairs gill arches. The first three are divided into four skeletal segments, the fourth and fifth arches are incomplete. The upper ends of the branchial arches are suspended from the base of the axial skull by double pharyngobranchial cartilages; the lower ones - to unpaired cartilages - copulas connecting the gill arches on the ventral side.

The operculum of sturgeons bears ossifications. The largest - axillary bone(suboperculum); Below it there are two smaller ossifications: superior and inferior.

Axial skeleton of the body. The basis of the axial skeleton of the body of cartilaginous ganoids is chord, or dorsal string (chorda dorsalis) (Fig. 30). On the outside, it is covered with a tight-fitting connective tissue sheath. There are no vertebral bodies. The cartilaginous upper and lower arches of the vertebrae are located on the shell of the chord. Superior caudal arches(arcus superior caudalis), or Basidorsalia(basidorsale), the right and left sides, merging, surround the spinal cord and form a tapering outgrowth above it, which ossifies and serves as the site of attachment of the unpaired dorsal spinous process(processus spinosus dorsalis). Between the bases of the upper caudal arches lie small intercalary cartilages - superior cranial arches(arcus superior cranialis), or interdorsals(interdorsale). On the ventral side of the notochord there is lower posterior arch, or, basiventralia(arcus ventralis posterior, s. basi ventrale). Between the lower posterior arches there are small cartilages on the sides - lower anterior arches(arcus ventralis anterior), or intercalated plates – interventralia(interventrale).

Figure 30 – Spine of sturgeon:

A- side view; b– cross section; 1 – superior caudal arch; 2 – neural canal; 3 – chord; 4 – hemal channel; 5 – ribs; 6 – lower posterior arch; 7 – superior cranial arches; 8 - dorsal spinous process.

In the trunk, the lower arches of the vertebrae form transverse processes(processus transversus), to which they are attached ribs(costa), well developed in the anterior part of the body. Their middle part is ossified, and the ends are cartilaginous. There are also small hemal processes covering the dorsal aorta, which close in the caudal part, forming hemal channel(canalis haemalis).

Skeleton of paired fins(Fig. 31). The pectoral fin girdle is represented by cartilage, in which one can distinguish: the ventral part – coracoid region(pars. coracoidea), dorsal part – scapular region(pars. scapularis) and mesocoracoid(mesocoracoideum). Above the scapular region lies a small suprascapular cartilage(cartilago suprascapularis). These are elements of the primary belt. On the outside it is covered with secondary cutaneous ossifications. The coracoid part of the primary girdle is covered by a steam room collarbone(clavicula) – a powerful covering bone. The middle part of the cartilaginous girdle covers the outside and front cleithrum(cleithrum). The upper part of the scapular region and the suprascapular cartilage of the girdle are covered supraclythrum(supracleithrum) and posterior cleithrum(postcleithrum). The supracleitrum is attached at its upper end to the outer roof of the skull.

Figure 31 – Skeleton of paired fins of a sterlet:

A– pectoral fin, right from the inside; b– pectoral fin, left from the outside; V– ventral fin; 1 – coracoid section; 2 – collarbone; 3 – cleithrum; 4 – supracleitrum; 5 – suprascapular cartilage; 6 – subcleitrum; 7 – scapular section; 8 – cartilaginous rays; 9 – lepidotrichia; 10 – mesocoracoid; 11 – basipterygium.

The pectoral fin skeleton consists of an internal and external skeleton. The internal skeleton is formed by a small (usually 8) number of cartilaginous rays, some of which are directly attached to the girdle, and some sit on a small main cartilage lying at the posterior edge of the fin. The external skeleton of the fin consists of bony, dissected skin rays - lepidotrichia, attached to the distal ends of the cartilaginous rays of the internal skeleton of the fin. The first ray of the pectoral fin is well developed and serves as an element by which the age of the fish is determined.

The pelvic girdle of sturgeons is not connected to the axial skeleton of the body. It is represented by two large spatulate cartilages - basipterygia(basipterygium). The cartilaginous rays of the internal skeleton of the ventral fin are attached to their distal ends.

The internal skeleton of the ventral fin, like the pectoral fin, consists of cartilaginous radial rays (not more than 10) in old fish, which are partially ossified. The exoskeleton is also represented by lepidotrichia.

Skeleton of unpaired fins. The internal skeleton of the dorsal and anal fins consists of cartilaginous dissected rays(radialia) (Fig. 32). Their bases are connected by connective tissue to the spinous processes of the vertebrae. The external skeleton of the fins is represented by lepidotrichia - skin bone rays. The number of lepidotrichia exceeds the number of radials.

The caudal fin is heterocercal. Its internal skeleton is made up of a thinning chord entering the upper lobe. The exoskeleton of the upper fin blade is presented fulcrs(fulcrum) and laterally with ganoid scales. The internal skeleton of the lower lobe of the caudal fin consists of weakly defined radials, and the external skeleton consists of lepidotrichia.

Figure 32 – Skeleton of the dorsal and anal fins of the sterlet:

1 – cartilaginous rays; 2 – lepidotrichia; 3 – chord.

Self-test questions:

1. What external signs are characteristic of sturgeon fish?

2. What are sturgeon bugs?

3. What mouth position is typical for sturgeon?

4. What are fulcra and where are they found?

5. Name the parts of the sturgeon heart.

6. Name all the organs of the digestive system.

7. Which glands are classified as digestive?

8. Name the hematopoietic organs of sturgeon.

9. What are the structural features of the sturgeon genitourinary system?

10. Describe the structure of the respiratory organs.

11. Name the sensory organs of sturgeon.

12. Describe the skeleton of the skull.

13. Describe the skeleton of the torso.

14. Describe the skeleton of paired and unpaired fins.

15. What structural features make cartilaginous ganoids similar to cartilaginous fish?

Topic 7. ANATOMICAL FEATURES OF BONE FISH
(TOPOGRAPHY OF INTERNAL ORGANS)

Material and equipment. Fresh fish (pike, carp, burbot, perch) and ready-made preparations (digestive system, injected circulatory system, brain of bony fish) - one for 2-3 students.

Tables: General location of internal organs; Digestive system of perch and carp; Circulatory system of bony fish; Excretory organs; Reproductive organs of male and female; Brain.

Dissecting instrument (scalpel, scissors, tweezers, dissecting needle) – one set for 2-3 students.

Bath – one for 2-3 students.

Introductory remarks. Bony fish (Teleostei), in contrast to cartilaginous ganoids, acquire a number of progressive features in their structure. Their skeleton is completely bone; the body is covered with bone scales; the spiral valve in the intestine disappears. Many species develop pyloric appendages, which increase the total absorptive surface of the intestine. The arterial conus of the heart (with the exception of some primitive forms) is replaced by the aortic bulb. The anus is moved away from the base of the ventral fins. Paired fins (especially pectoral fins) are located in a vertical plane.

During laboratory classes, it is recommended to study the features of the external and internal structure of representatives of four orders of bony fish, located at different levels of evolutionary development of the perch (Perca fluviatilis L.) from the order Perciformes; burbot (Lota lota L) from the order Gadiformes, carp (Cyprinus carpio L.) from the order Cypriniformes and pike (Esox lucius L.) from the order Esociformes. The main object of study is perch; other species are considered from a comparative perspective.

Exercise. Based on knowledge of the external characteristics of fish, it is recommended to independently consider the features of the external structure of the above species of fish and fill out the table. 1.

Table 1

Having filled out the table, you can begin opening the fish, for which you need the following

1. Using scissors, make a short transverse incision in the abdominal wall in front of the anus.

2. Carefully insert the blunt end of the scissors into the incision and make an incision along the abdominal side of the body to the head up to the mouth. In this case, you need to press the scissors from the bottom up without pushing their ends deep, so as not to damage the internal organs.

3. From the beginning of the longitudinal incision (at the anus), make another incision - upward towards the lateral line.

4. Raising the side wall of the body, cut forward along the spine to the gill cover, separating the side wall of the body.

5. Cut off the gill cover.

6. Carefully, using tweezers, a scalpel and needles, free the preparation from pieces of muscle and films that interfere with examination.

7. Consistently consider the structure of various systems of internal organs in the following order:

respiratory organs: four pairs of gills;

digestive system: oral cavity, pharyngeal teeth and grinder (in carp), pharynx, esophagus, stomach, intestines, pyloric outgrowths (in burbot and perch), liver, gall bladder, pancreas, anus;

circulatory system: heart (atrium and ventricle), aortic bulb, venous sinus, abdominal and dorsal aorta;

excretory organs: kidneys, ureters, bladder;

reproductive organs: testes, ovaries, genital ducts, genital opening;

swim bladder;

central nervous system: forebrain, diencephalon, midbrain, cerebellum and medulla oblongata.

Having examined the general location and structure of organ systems in dissected fish, you should fill out the table. 2, and then move on to studying organ systems using ready-made preparations and tables. This is especially true for the peripheral circulatory and central nervous systems.

General topography of internal organs. Under the operculum lie four pairs of gill arches (arcus branhialis) (Fig. 33). Behind them, in the pericardial cavity, the walls of which are lined with pericardium, there is a two-chambered heart (cor). The pericardium covers the parts of the heart from the outside and is called here the epicardium.

table 2

In the abdominal part of the pericardial cavity lies a muscular ventricle(ventriculus), dark red edges protrude from under it on both sides atria(atrium). In carp, the atrium almost completely covers the ventricle.

Figure 33 – General topography of the internal organs of bony fish:

A- pike; b– perch; V– carp; 1 – gill; 2 – false gill; 3 - heart; 4 - liver; 5 - stomach; 6 - intestines; 7 – pyloric appendages; 8 – anus; 9 – spleen; 10 - pancreas; 11 – gonad; 12 – genital opening; 13 – swim bladder; 14 – kidney; 15 – head kidney; 16 – bladder; 17 - urinary opening.

Adjacent to the posterior part of the atrium is a thin-walled venous sinus(sinus venosus). Stretch forward from the heart abdominal aorta(aorta ventralis), at the base of which there is an extension - aortic bulb(bulbusaortae).

The pericardial cavity is followed by the abdominal cavity, separated by a thin transverse septum. It contains all the internal organs of the body. In perch and burbot they occupy a relatively small volume, which is associated with the higher organization of these fish.

In the anterior part of the abdominal cavity there is liver(hepar). In perch it is single-lobed and occupies the left front part of the cavity.

The pike liver is also single-lobed and lies in the left abdominal part of the anterior cavity. The large liver of burbot with a large reserve of fat, like all cod fish, occupies a significant part of the abdominal cavity. The liver of carp is large. Two of its blades are visible on the surface of the intestine in the anterior part of the cavity and one, large one, in the middle part of the intestine under the gonad. On the inside of the liver of all fish is visible gallbladder(vesica fellea).

Covers the liver stomach(gaster), isolated in the form of a blind outgrowth in perch and burbot. In carp and pike, it looks like an elastic tube, externally indistinguishable from the esophagus. The intestines begin from the stomach. Directly near the stomach of perch and burbot, blind outgrowths extend from the intestines - pyloric appendages(appendix pylorica). In one of the intestinal loops under the stomach lies a dark brown spleen(lien). Pancreas(pancreas) in a dispersed state is scattered throughout the mesentery (in carp also in the liver); Only in pike it is formed and lies along the bile duct. At the back of the body cavity are the genital organs - testes(testis) or ovaries(ovarium). The degree of their development depends on the time of year and the age of the fish. Located deepest of all organs under the spine swim bladder(vesica pneumatica), which is a protrusion of the upper wall of the anterior part of the digestive tube. Perch and burbot have a single swim bladder, attached with the upper wall to the spine. In adult fish, the swim bladder has no connection with the esophagus.

By opening the swim bladder, you can find gas glands, or red body (corpus ruber), in the form of small lobes on the ventral wall of the anterior part. The central part of the gas glands is occupied by a plexus of blood vessels, and the edges are formed by the substance of the gland. Gases enter the swim bladder through the gas gland. The release of gases in closed-vesical fish occurs with the help of an oval lying on the dorsal side of the back of the swim bladder. An oval is a hole in the inner shell of the swim bladder, equipped with muscles at the edges, due to which the size of the hole changes. The pike's swim bladder, in the form of a long sac, is located near the spine and is tightly connected to it.

Pike belongs to the open-bladder fish, and its swim bladder is connected to the esophagus through a small air channel(ductus pneumaticus), located in the front of the swim bladder and serves to remove gases. The carp swim bladder lies freely in the body cavity and consists of two sections: anterior and posterior. The carp's air duct extends from the front of the hindquarters. The supply of gases, as in all open-vesical fish, occurs through the gas gland, located on the ventral side inside the front part of the swim bladder.

Above the swim bladder, dark red buds (ren) stretch along the spine, the anterior ends of which form the head bud, which is especially well developed in carp. Its anterior part goes under the shoulder girdle and descends almost to the level of the upper edge of the pectoral fin, located dorsal to the pericardial cavity.

Respiratory system. In bony fishes, the respiratory organs are gills of ectodermal origin. Teleosts have 4 gill arches with 4 complete gills and one semi-gill on the inside of the operculum. Unlike cartilaginous ganoids, which retain the interbranchial septum, teleost fish completely lose it.

Each gill (branchia) consists of two parts: the upper, shorter, and the lower, longer. At the base of the gill lies a bone gill arch(arcus branchialis) (Fig. 34). In cross section it has U-shape. On the inside of each gill arch there are whitish gill rakers directed towards the adjacent gill arch. Bright red gill filaments(filum branchialis) sit along the posterior edge of the gill arch. This is where gas exchange occurs. The gill filaments are located on the gill arch in two rows, and their free edge hangs into the gill cavity. false gill(pseudobranchia) in all fish under consideration lies on the inside of the gill cover. In perch, the gill filaments are clearly visible in it; in pike and carp it looks like a reddish translucent spot.

Figure 34 – Gill apparatus of bony fish:

1 – first gill arch; 2 – gill rakers; 3 - gill filaments.

Digestive system. In bony fishes, the digestive tract begins mouth opening(rima oris). The mouth of perch, burbot and pike is armed teeth(dens), in carp it is toothless.

The perch's teeth are small, sitting on both jaws and the front of the palate, where they are connected to the vomer, premaxillary and palatine bones. Burbot and pike have large teeth, and in pike the largest teeth are on the lower jaw, and smaller ones are on the intermaxillary bones of the upper jaw; the teeth on the vomer, premaxillary palatine bones and on the tongue have the appearance of a grater. The teeth of predatory fish perform the function of holding food.

The mouth opening leads to oral cavity(cavum orale), which without a clear boundary passes into throat(pharynx). In the oropharyngeal cavity, on the inside of the gill arches there are gill rakers. The gill rakers form a filtering apparatus that prevents food particles from exiting the pharynx through the gill cavity to the outside. In fish that feed on plankton, they are long, thick, in predators they are short, sparse, and hard. The nature and number of gill rakers is an important systematic feature for many species. In the species under consideration, the nature of the gill rakers is correspondingly different. In perch, burbot and pike, the gill rakers are sparse, short, hard, with teeth on the surface; in carp - elastic with dissected edges.

The pharyngeal teeth are located in the posterior part of the oropharyngeal cavity. Perch, burbot and pike have upper and lower pharyngeal teeth. In cyprinids, the upper pharyngeal teeth are absent, but the lower pharyngeal teeth are well developed; The function of the upper pharyngeal teeth in them is performed by a horny formation - a millstone located on the roof of the oropharyngeal cavity above the pharyngeal teeth. The number and structure of pharyngeal teeth is an important systematic feature of the carp family (Fig. 35). The pharyngeal teeth of carp look like three rows of large white tubercles with a chewing surface.

Figure 35 – Pharyngeal apparatus in carp fish:

1 – millstone; 2 - pharyngeal bones.

The pharynx becomes short esophagus(oesophagus), followed by stomach(gaster). In perch and burbot, the stomach is isolated in the form of a blind outgrowth; in pike, it is externally a direct continuation of the esophagus (Fig. 36). The stomach walls of predators are thick, muscular and elastic; a stomach filled with food can stretch greatly. Carp have no stomach.

Figure 36 – Part of the digestive tract and swim bladder of fish:

A– perch; b– carp; V– pike; G– burbot; 1 - stomach; 2 – pyloric appendages; 3 – spleen; 4 - intestines; 5 – gallbladder; 6 - liver; 7 – swim bladder; 8 - air channel.

Intestines(intestinum) of perch, burbot and pike is poorly differentiated into the duodenum (duodenum), small (intestinum) and rectum (rectum). The carp intestine is a histologically homogeneous tube, which is conventionally divided into anterior (slightly expanded), middle and posterior sections. In perch and burbot, at the beginning of the intestine there are blind outgrowths - pyloric appendages(appendix pylorica). The rectum of predators and the hind intestine of carp end anus(anus), lying on the ventral side of the body in front of the urinary and genital openings.

The digestive glands - the liver and pancreas - flow through their ducts into the anterior part of the intestine. Liver(hepar) is located in the anterior abdominal cavity. In perch and pike it is single-lobed and large. It is especially large and pale-colored in burbot due to its high fat content. The carp liver consists of two lobes with processes. The left lobe lies to the left of the initial section of the intestine. It has a small outgrowth lying in a loop of intestine. The right lobe is located to the right of the anterior intestine and occupies the entire right side of the anterior part of the body cavity. It has a long process that lies along the ventral side of the swim bladder almost to the posterior end of the body cavity. The same process on the left side in the form of a blade enters the loop of the hind and middle intestines. In carp, the liver includes pancreatic tissue and is called the hepatopancreas. On the inside of the liver (in carp between the two lobes) there is gallbladder(vesica fellea). The bile duct drains bile into the anterior intestine.

Pancreas(pancreas) of perch, burbot and carp is scattered in the form of small fat-like inclusions in the liver, near the gallbladder and its ducts, the spleen, and also along the intestinal walls. Only in pike is it isolated and lies along the bile duct.

Circulatory system. Heart(cor) is located in the lower anterior part of the body cavity. It consists of three departments: venous sinus(sinus venosus), venous blood collects in it; atria(atrium) and ventricle(ventriculus) (Fig. 37). Blood in the heart

Figure 37 – Circulatory system of bony fish:

1 – ventricle; 2 – atrium; 3 – aortic bulb; 4 – abdominal aorta; 5 – roots of the aorta; 6 – afferent branchial arteries; 7 – efferent branchial arteries; 8 – anterior cardinal veins; 9 – duct of Cuvier; 10 – dorsal aorta; 11 – left posterior cardinal vein; 12 – renal portal system; 13 – tail vein; 14 – right posterior cardinal vein; 15 – subintestinal vein; 16 – portal system of the liver; 17 – hepatic vein (vessels with venous blood are painted black).

fish only venous. Unlike cartilaginous fish, teleost fish do not have a fourth section, the conus arteriosus. A large vessel departs directly from the ventricle - abdominal aorta(aorta ventralis), forming an expansion at the very beginning - aortic bulb(bulbus aortae). The aortic bulb is not a part of the heart and does not bear striated muscles. Four pairs of afferent gill arteries (arteria branchialis efferentia) depart from the abdominal aorta, which break up into capillaries in the gill filaments. Here gas exchange occurs, and oxygenated arterial blood is collected through the capillary system into the efferent branchial arteries (arteria branchialis afferentia). The latter on the dorsal side flow into the paired roots of the dorsal aorta. The roots of the aorta (radix aortae) enter the opening in the parasphenoid bone and merge there. A head circle of blood circulation is formed. In the posterior part of the head, the roots of the aorta also merge, forming the unpaired dorsal aorta (aorta dorsalis) - a large vessel running along the spine and directly adjacent to it. It is clearly visible on the opened fish after removing the entrails.

Venous blood from the caudal region passes through the azygos caudal vein (vena caudalis), which bifurcates into the kidneys. Only in the left kidney does a portal system form, which is also clearly visible on fresh fish. This bud has a darker color. From the kidneys, blood flows forward through the posterior cardinal veins (vena cardinalis posterior). The posterior cardinal veins at the level of the heart merge with the anterior cardinal veins (vena cardinalis anterior), which carry blood from the head. By the fusion of the anterior and posterior cardinal veins, the ducts of Cuvier (ductus cuvieri) are formed, which flow into the venous sinus. From the intestine, blood through the portal vein of the liver (vena porta hepatis) enters the liver, where it breaks down into a system of capillaries, forming the portal system of the liver. Next, the blood enters the venous sinus through the hepatic vein (vena hepatica). Bony fish have one closed blood circulation.

The hematopoietic organ of bony fishes is spleen(lien), lying in one of the intestinal loops and having a dark burgundy color.

Excretory organs. Unlike cartilaginous ganoids, the excretory system (kidneys, ureter) of bony fishes is not connected with the reproductive organs (Fig. 38).

Figure 38 – Excretory canals of the genitourinary system of pike:

1 – kidneys; 2 – ureter; 3 – external opening of the ureter; 4 – genital opening; 5 – anus; 6 – bladder; 7 – vas deferens; 8 - intestines; 9 – testis.

Kidneys(ren) of bony fishes, the mesonephric (trunk) lie on the sides of the spine above the swim bladder. The anterior, somewhat widened ends form the head bud, which is well defined in perch and carp. In the posterior part, the right and left kidneys merge. Along the inner edge of the kidneys there are ureters(ureter), which in the posterior section merge together and flow into the unpaired duct bladder(vesica urinaria). An unpaired duct departs from the latter, opening outward next to the genital opening.

Reproductive organs. In males they are represented by testes, in females by ovaries and are located on the sides of the swim bladder (see Fig. 38). The degree of their development depends on the time of year and the age of the fish. Testes(testis) – long dense paired formations. Along their upper edge there are vas deferens(ductus spermaticus), opening outwards with a small common genital opening. Ovaries(ovarium) in burbot, pike and carp are paired. Perch has an unpaired ovary. The posterior elongated sections of the ovaries pass into oviducts(oviductus), opening with an unpaired genital opening.

Central nervous system and sensory organs. The brain of teleosts is represented by five sections typical for most vertebrates (Fig. 39).

Figure 39 – Brain of bony fish:

A– pike (top view); b– pike (bottom view); c – carp; G– perch; 1 – forebrain hemispheres; 2 – olfactory bulbs; 3 – lower lobes of the diencephalon; 4 – pineal gland; 5 – cross; 6 – optic lobes of the midbrain; 7 – cerebellum; 8 - medulla; 9 – rhomboid lobule of the medulla oblongata; 10 - head nerves.

The forebrain (telencephalon) is small in size compared to other parts. The roof of the cerebral hemispheres is epithelial and does not contain nerve cells. The mass of the forebrain consists of the striatum. Adjacent to the anterior edge of the brain are small oblong-oval olfactory bulbs(bulbus olfactorius), the olfactory nerves come from them. In carp, unlike pike and perch, the olfactory bulbs are adjacent directly to the olfactory capsules.

The diencephalon is covered by the midbrain hanging above it. In the posterior part of the diencephalon there is a small club-shaped outgrowth - the pineal gland (epiphysis).

The midbrain (mesencephalon) is well developed. In its dorsal part there are two large oval optic lobes (lobus opticus). These are the visual centers where the fibers of the optic nerve end. In carp, the optic lobes reach significant development.

Directly behind the optic lobes lies cerebellum(cerebellum) round in shape, large in size. It adjoins the medulla oblongata with its posterior edge.

The anterior part of the medulla oblongata (myelencephalon) extends under the cerebellum, and at the back it gradually passes into the spinal cord. Most of the brain nerves arise from the medulla oblongata. At its bottom lies the respiratory center.

On the lower surface of the brain there are large optic nerves that go to the base of the skull and form cross, or chiasmus. On the lower side of the diencephalon, adjacent to the posterior edge of the chiasm, lies a small rounded outgrowth - pituitary(hypophysis).

Bony fish distinguish smells, taste, hear, see and perceive environmental fluctuations.

The olfactory organs are represented by paired sacs that open outward through the nasal openings (Fig. 40). The bottom of the bags is folded with olfactory cells. The olfactory nerve extends from the olfactory sacs to the forebrain.

Figure 40 – Nasal cavity of a fish:

1 – anterior nasal opening; 2 – fold of skin; 3 – posterior nasal opening; 4 – folds of the mucous membrane with the olfactory epithelium.

The hearing organ consists of two parts: oval pouch(utriculus) with three extending from it in mutually perpendicular planes semicircular canals(canalis semicircularis) and located under it round pouch(sacculus). The round pouch is usually equipped with a blind pouch-shaped outgrowth - snail(lagena). The largest otolith (sagetta) is located in the round sac. On the medial side, branches of the auditory nerve approach the round sac. All parts of the labyrinth are filled with endolymph; between the wall of the labyrinth and the wall of the cavity in which it lies, there is perilymph.

Taste organs in the form of microscopic sensitive buds are scattered both in the oral cavity and throughout the body of bony fish. They are located in sensory pits lined with long supporting cells, between which sensory cells lie. They are especially developed in bottom fish, located on the outer surface of the head, antennae and belly.

The organs of vision are represented by paired spherical eyes. The eye consists of several layers: outer - sclera(sclera), passing in the anterior part into cornea(cornea); vascular(chorioidea), passing on the outside into iris(iris), which surrounds a large spherical lens(lens). The inner layer of the eye wall is lined retina(retina). The sclera is lined on the inside silver shell(argentea) – cells containing guanine crystals. At the base of the eye, at the entry point of the optic nerve, is located, characteristic of fish eyes vascular gland(glandula chorioidea).

Seismosensory organs are represented by a system of channels passing inside the walls of the body, with branches to the surface, the ends of which either have holes or are covered with a membrane. The bottom of the canals is lined with sensitive cells that perceive vibrations in the aquatic environment. The main channel is the lateral line of the fish. Some of the channels of the seismosensory system are concentrated on the head of the fish. In all bony fishes, the arrangement of the canals on the head is very similar. In some, they open outward with a series of holes (pike) or channels (perch) (Fig. 41). In other fish, the canals run deep into the integumentary bones and are not externally visible.

Figure 41 – Diagram of the seismosensory system on the head of pike (a) and perch (b):

1 – postorbital canal; 2 – supraorbital canal; 3 – infraorbital canal; 4 – hyomandibular canal.

Self-test questions:

1. What type of scales do pike, carp, burbot, and perch have?

2. Describe the structure of the teeth of pike, burbot and perch.

3. What are pharyngeal teeth and burrs?

4. What are gill rakers, where are they located, what is their function?

5. Name the sections of the digestive tract of perch, burbot, pike and carp. What glands are associated with the digestive tract?

6. Which species of the fish considered have a stomach and which do not?

7. Which of the above fish are open-vesical and which are closed-vesical?

8. Describe the structure of the circulatory system of bony fish.

9. In what part of the body is the heart located in fish and what parts does it consist of?

10. The structure of the excretory system of bony fish.

11. Reproductive organs of bony fish. Which fish have an unpaired ovary?

12. What sections are distinguished in the brain of bony fish?

13. Where is the pituitary gland located?

Characteristic features of chordates:

• three-layer structure;
• secondary body cavity;
• the appearance of a chord;
• conquest of all habitats (water, land and air).

During evolution, organs improved:

• movements;
• reproduction;
• breathing;
• blood circulation;
• digestion;
• feelings;
• nervous (regulating and controlling the work of all organs);
• body coverings changed.

Biological meaning of all living things:

They live in freshwater bodies of water; in sea water.

Life expectancy ranges from several months to 100 years.

Dimensions - from 10 mm to 9 meters. (Fish grow all their lives!).

Weight - from a few grams to 2 tons.

Fish are the most ancient proto-aquatic vertebrates. They are able to live only in water; most species are good swimmers. The class of fish in the process of evolution was formed in the aquatic environment, and the characteristic structural features of these animals are associated with it. The main type of translational movement is lateral wave-like movements due to contractions of the muscles of the tail or the whole body. The pectoral and ventral paired fins serve as stabilizers, used to raise and lower the body, turn stops, slow smooth movement, and maintain balance. The unpaired dorsal and caudal fins act as a keel, giving stability to the fish's body. The mucous layer on the surface of the skin reduces friction and promotes rapid movement, and also protects the body from pathogens of bacterial and fungal diseases.

External structure of fish

Side line

The lateral line organs are well developed. The lateral line perceives the direction and strength of water flow.

Thanks to this, even when blinded, it does not bump into obstacles and is able to catch moving prey.

Internal structure

Skeleton

The skeleton is the support for well-developed striated muscles. Some muscle segments were partially rebuilt, forming muscle groups in the head, jaws, gill covers, pectoral fins, etc. (ocular, epibranchial and hypobranchial muscles, muscles of paired fins).

swim bladder

Above the intestines there is a thin-walled sac - a swim bladder, filled with a mixture of oxygen, nitrogen and carbon dioxide. The bladder formed from an outgrowth of the intestine. The main function of the swim bladder is hydrostatic. By changing the pressure of gases in the swim bladder, the fish can change the depth of its dive.

If the volume of the swim bladder does not change, the fish is at the same depth, as if hanging in the water column. When the volume of the bubble increases, the fish rises. When lowering, the reverse process occurs. The swim bladder of some fish can participate in gas exchange (as an additional respiratory organ), serve as a resonator when producing various sounds, etc.

Body cavity

Organ system

Digestive

The digestive system begins with the mouth. Perch and other predatory bony fish have numerous small, sharp teeth on their jaws and many bones in their mouths that help them capture and hold prey. There is no muscular tongue. Through the pharynx into the esophagus, food enters the large stomach, where it begins to be digested under the influence of hydrochloric acid and pepsin. Partially digested food enters the small intestine, where the ducts of the pancreas and liver empty. The latter secretes bile, which accumulates in the gallbladder.

At the beginning of the small intestine, blind processes flow into it, due to which the glandular and absorptive surface of the intestine increases. Undigested residues are excreted into the hindgut and removed through the anus.

Respiratory

The respiratory organs—gills—are located on four gill arches in the form of a row of bright red gill filaments, covered on the outside with numerous thin folds that increase the relative surface of the gills.

Water enters the fish's mouth, is filtered through the gill slits, washes the gills, and is thrown out from under the gill cover. Gas exchange occurs in numerous gill capillaries, in which blood flows towards the water washing the gills. Fish are able to absorb 46-82% of oxygen dissolved in water.

Opposite each row of gill filaments are whitish gill rakers, which are of great importance for the nutrition of fish: in some they form a filtering apparatus with a corresponding structure, in others they help retain prey in the oral cavity.

Blood

The circulatory system consists of a two-chambered heart and blood vessels. The heart has an atrium and a ventricle.

excretory

The excretory system is represented by two dark red ribbon-like buds, lying below the spinal column almost along the entire body cavity.

The kidneys filter waste products from the blood in the form of urine, which passes through two ureters into the bladder, which opens outward behind the anus. A significant part of the toxic decomposition products (ammonia, urea, etc.) are excreted from the body through the gill filaments of fish.

Nervous

The nervous system looks like a hollow tube thickened in front. Its anterior end forms the brain, which has five sections: the forebrain, diencephalon, midbrain, cerebellum and medulla oblongata.

The centers of different sense organs are located in different parts of the brain. The cavity inside the spinal cord is called the spinal canal.

Sense organs

Taste buds, or taste buds, are located in the mucous membrane of the oral cavity, on the head, antennae, elongated fin rays, and scattered over the entire surface of the body. Tactile corpuscles and thermoreceptors are scattered in the superficial layers of the skin. Receptors of electromagnetic sense are concentrated mainly on the head of fish.

Two large eyes are located on the sides of the head. The lens is round, does not change shape and almost touches the flattened cornea (therefore fish are myopic and see no further than 10-15 meters). In most bony fishes, the retina contains rods and cones. This allows them to adapt to changing light conditions. Most bony fish have color vision.

The hearing organs are represented only by the inner ear, or membranous labyrinth, located on the right and left in the bones of the back of the skull. Sound orientation is very important for aquatic animals. The speed of sound propagation in water is almost 4 times greater than in air (and is close to the sound permeability of fish body tissues). Therefore, even a relatively simple organ of hearing allows fish to perceive sound waves. The hearing organs are anatomically connected to the balance organs.

From the head to the caudal fin, a series of holes stretches along the body—the lateral line. The holes are connected to a channel immersed in the skin, which branches strongly on the head and forms a complex network. The lateral line is a characteristic sensory organ: thanks to it, fish perceive water vibrations, the direction and strength of the current, and waves that are reflected from various objects. With the help of this organ, fish navigate in water flows, perceive the direction of movement of prey or predators, and do not bump into solid objects in barely transparent water.

Reproduction

Fish breed in water. Most species lay eggs, fertilization is external, sometimes internal, and in these cases viviparity is observed. The development of fertilized eggs lasts from several hours to several months. The larvae that emerge from the eggs have a remnant of the yolk sac with a supply of nutrients. At first they are inactive and feed only on these substances, and then they begin to actively feed on various microscopic aquatic organisms. After a few weeks, the larva develops into a small fish covered with scales and resembling an adult fish.

Fish spawn at different times of the year. Most freshwater fish lay their eggs among aquatic plants in shallow water. The fertility of fish, on average, is much higher than the fertility of terrestrial vertebrates; this is associated with a large loss of eggs and fry.

Anatomy of fish: structure, shape, color

Digestive system in bony fishes the structure is a little more complicated than in cartilaginous fishes. This is primarily due to differences in the diet of some and others. The digestive system of fish is divided into three parts: the anterior (mouth, pharynx and esophagus), middle (stomach, small intestine, liver and pancreas, digestive glands) and posterior (large intestine).

Found in fish three types of oral cavity:

— grasping- when predatory fish have jaws with sharp teeth;

— suction- when the mouth looks like a suction tube (bream);

— crushing- when the jaws are dotted with large but blunt teeth (catfish).

In some planktivorous fish species (herring, silver carp, etc.), the gill apparatus is also involved in the digestive process, holding small animals and sending them to the stomach. Stomach All fish except cyprinids have it. Intestines can be of different lengths, depending on the nature of the fish’s diet. In herbivores it is longer, in predators it is shorter.

In the intestines of some fish species there are pyloric appendages- special outgrowths that increase the absorption capacity of the intestine and allow you to absorb the maximum amount of nutrients from food. Fish do not have salivary glands. Food is digested using enzymes, which are secreted by the pancreas, liver and intestinal glands.

Additional materials on the topic: Digestive system of fish.

The digestive system of fish is relatively simple, but in many cases unique.

It varies among different species of fish, including depending on the type of food.

The structure of the digestive system

The general “framework” of the fish digestive system is as follows:

• Oral cavity;
• Pharynx;
• Esophagus;
• Stomach;
• Intestines. The intestine consists of the rectum, colon, small intestine and anus.

There are fish that also have a cloaca - a hollow organ in which the rectum and ducts of the reproductive and urinary systems are located; this organ is characteristic of cartilaginous and lungfishes.

Not all fish have a stomach. For example, many cyprinids do not have it. Their food is digested in the intestines themselves. Predators most often have a developed stomach.

It can have a different structure: in the form of a tube, an oval cavity, and even in the shape of the Latin letter V. Substances that break down food in the stomach are pepsin and hydrochloric acid.

Oral cavity

The oral cavity of fish does not have salivary glands. Cyclostomes (lampreys, hagfish), which are sometimes classified as “primitive fish,” have these glands, but they are vital for them: these organisms stick to the victim, pierce its skin with a sharp tongue and inject saliva inside, which dissolves the proteins; In this way, external digestion of food is carried out, which is then absorbed by the animal in liquid form.

However, real fish have taste buds and, therefore, are able to distinguish food by taste. Most predators have teeth, as well as those herbivores that have to grind hard parts of plant food.

fish structure photo

Teeth can often be arranged in several rows and be present not only on the gums, but also in other places in the mouth and on the tongue. Fish teeth are nothing more than modified placoid scales; They do not have roots, but they are constantly renewed - new ones grow in place of those that fall out.

By the way, fish also lack a real tongue; its role is played by the copula (part of the hyoid arch). It does not have its own muscles, unlike the tongue of other groups of animals. Fish that feed on benthos (small bottom-dwelling animals) often have a tubular mouth designed for suction.

Pharynx

The pharynx of fish is often also studded with teeth, the number and structure of which are different. Pharyngeal teeth are necessary for holding and grinding swallowed food; in cyprinids, the same function is performed by the horny organ on the upper part of the pharynx - the philtrum.

Digestive system of fish

Has a pharynx and gill rakers; in predatory species they are short and few in number, while in planktivorous species the stamens are long and numerous, designed to filter ingested food. The pharynx and oral cavity of fish have glands, but they do not produce saliva as such, but simply mucus, which makes it easier to swallow prey.

After the pharynx comes the esophagus, which is small in most fish. In some fish, such as pufferfish, the esophagus also acts as an air sac and is adapted to inflate the body.

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Digestive system of fish

The digestive system of fish is represented by the digestive tract and digestive glands.

The digestive tract includes:

1) oral cavity;

2) pharynx;

3) esophagus;

4) stomach;

5) intestines.

Depending on the feeding habits of the fish, these sections vary significantly. Cyclostomes have a sucking type of mouthparts; it begins with a suction funnel, at the bottom of which there is a mouth opening. On the inner surface of the funnel there are horny teeth. In the depths of the funnel there is a powerful tongue with teeth. Using a funnel, cyclostomes attach themselves to the victim and drill into its body with their tongue. Near the tongue there are paired salivary glands that secrete substances into the wound that prevent blood clotting and dissolve proteins. Thus, partially digested food enters the oral cavity.

Predatory fish have a large, grasping mouth armed with teeth. Many benthivorous fish have a tube-shaped suction mouth (cyprinid, pipefish); planktivorous - large or medium-sized mouth with or without small teeth (whitefish, herring, etc.); periphytonivores - a mouth in the form of a transverse slit located on the underside of the head, the lower lip is covered with a horny sheath (podust, khramulya).

Most fish in the mouth cavity on the jaws have teeth, which are modified placoid scales. Tooth includes:

1) vitrodentin (outer enamel-like layer);

2) dentin (lime-impregnated organic matter);

3) pulp (a cavity filled with connective tissue with nerves and blood vessels).

Teeth, as a rule, do not have roots and are replaced with new ones as they wear out. In whole-headed and lungfishes, teeth grow continuously; Many peaceful species do not have teeth in the oral cavity (cyprinids).

Teeth can be located not only on the jaws, but also on other bones of the oral cavity and even on the tongue. Predatory fish have sharp, recurved teeth that are used to grasp and hold prey. Many stingrays have flat teeth. In catfish, the front teeth are conical and are designed for grasping prey, and the lateral and rear teeth are flattened for crushing shells of mollusks, etc.

Fish do not have a real tongue, which has its own muscles. Its role is played by the unpaired element of the hyoid arch (copula).

The oral cavity of fish passes into the pharynx, the walls of which are pierced by gill slits with gill arches that open outward. On the inside of the gill arches there are gill rakers, the structure of which depends on the feeding pattern of the fish. In predatory fish, gill rakers are few in number, short and are designed to protect the gill filaments and retain prey; in planktivores - numerous, long, used for straining food organisms. The number of gill rakers on the first gill arch is a systematic feature for some species (coregonids).

In some fish, a special epibranchial organ develops in the dorsal wall of the pharynx, which serves to concentrate small food (silver carp).

Predatory fish have:

1) upper pharyngeal teeth (on the upper elements of the gill arches);

2) lower pharyngeal teeth (on the fifth underdeveloped gill arch).

The pharyngeal teeth look like platforms covered with small teeth and serve to hold prey.

Cyprinid fish have highly developed lower pharyngeal teeth, which are located on the fifth underdeveloped gill arch. On the upper wall of the throat of cyprinids there is a hard horny formation - a millstone, which is involved in grinding food. The pharyngeal teeth can be single-row (bream, roach), double-row (bream, shemaya), three-row (carp, barbel). Pharyngeal teeth are replaced annually.

In the oral and pharyngeal cavities of fish there are glands, the mucus of which does not contain digestive enzymes, but facilitates the swallowing of food.

The pharynx passes into a short esophagus. In representatives of the order Pufferfish, the esophagus forms an air sac, which serves to inflate the body.

In most fish, the esophagus goes into the stomach. The structure and size of the stomach are related to the nature of nutrition. Thus, pike has a stomach in the form of a tube, perch has a blind outgrowth, some fish have a curved stomach in the shape of the letter V (sharks, rays, salmon, etc.), which consists of two sections:

1) cardiac (anterior);

2) pyloric (posterior).

In cyclostomes, the esophagus passes into the intestine. Some fish do not have a stomach (cyprinids, lungfishes, wholeheads, gurnards, many gobies, monkfish).

Digestive system of fish.

Food from their esophagus enters the intestine, which is divided into three sections: anterior, middle and posterior. The ducts of the liver and pancreas empty into the anterior part of the intestine.

To increase the absorption surface, the fish intestine has a number of features:

1) folded inner surface;

2) spiral valve - an outgrowth of the intestinal wall (in cyclostomes, cartilaginous fish, cartilaginous and bony ganoids, lungfishes, lobe-finned fishes, salmonids);

3) pyloric appendages (herring, salmon, mackerel, mullet); appendages extend from the anterior intestine, gerbils have one appendage, river perch have three, mackerel have about 200; in sturgeons, the pyloric appendages have fused and formed the pyloric gland, which opens into the intestine; the number of pyloric appendages in some species is a systematic feature (salmon, mullet);

4) increase in intestinal length; length is related to the calorie content of food; Predatory fish have a short intestine; silver carp, which feeds on phytoplankton, have an intestinal length 16 times longer than the body.

The intestine ends with the anus, which is usually located in the back of the body in front of the genital and urinary openings. In cartilaginous and lungfishes, the cloaca is preserved.

Digestive glands. The ducts of two digestive glands flow into the anterior intestine: the liver and pancreas.

Cartilaginous fish have a large three-lobed liver (10-20% of body weight). In bony fish, the liver may consist of one, two or three lobes. The liver produces bile, which emulsifies fats and enhances intestinal motility. The liver also neutralizes toxic substances coming from the intestines, synthesizes proteins and carbohydrates, and accumulates glycogen, fat, and vitamins (sharks, cod).

Cartilaginous and large sturgeon fish have a separate pancreas. In many fish, pancreatic tissue is located in the liver and is called hepatopancreas (cyprinid); in some fish it is located near the gallbladder and its ducts, the spleen, and in the intestinal mesentery. The pancreas secretes enzymes into the intestines that digest fats, proteins and carbohydrates. Islet cells (endocrine) produce the hormone insulin, which regulates blood sugar levels.

It is believed that the pyloric appendages, along with increasing the absorption surface, have an enzymatic function. In addition to their own digestive enzymes, herbivorous fish species participate in digestion by enzymes secreted by microorganisms that constantly live in the intestines (symbiotic digestion).

Fish body cavity

In the body section of the fish, under the spine, there is a large body cavity in which the internal organs are located.

Figure: Internal structure of river perch. Digestive and excretory systems

The digestive system of fish using the example of river perch

Perch is a predator. It feeds on a variety of aquatic animals, including other species of fish. The perch captures and holds its prey with sharp teeth sitting on its jaws. After swallowing, food passes through the pharynx and esophagus into the stomach. Perch swallows its prey whole, and therefore its stomach has the ability to greatly stretch. Microscopic glands of the stomach walls secrete gastric juice. Under its influence, food begins to be digested. The partially modified food then passes into the small intestine, where it is acted upon by the digestive juice of the pancreas and bile coming from the liver. The supply of bile accumulates in gallbladder. Nutrients penetrate through the walls into the blood, and undigested residues enter the hindgut and are thrown out.

The respiratory system of fish using the example of river perch

Fish breathe oxygen dissolved in water, constantly swallowing water. From the oral cavity, water passes through gill slits, which permeate the walls of the pharynx, and washes the respiratory organs - gills. In perch, they consist of gill arches, on each of which they sit on one side bright red gill filaments, and on the other - whitish gill rakers. Gill rakers are a filtering apparatus: they prevent prey from slipping out through the gill slits. The gill filaments are penetrated by the smallest blood vessels - capillaries. Through the thin walls of the gill filaments, oxygen dissolved in water penetrates into the blood, and carbon dioxide is removed from the blood into the water.

If there is little oxygen, then the fish rise to the surface and begin to take in air with their mouths. Prolonged exposure to water containing little oxygen can cause fish death. In winter, there is sometimes a lack of oxygen under ice in reservoirs. Then the fish die. To prevent freezing, it is useful to make holes in the ice.

Dried gill filaments cannot allow oxygen and carbon dioxide to pass through. Therefore, fish taken out of the water quickly die. On the outside, the delicate gills are covered with gill covers.

The circulatory system of fish using the example of river perch

Figure: Internal structure of river perch. Circulatory system

Figure: Structure and function of river perch gills

The circulatory system of fish is closed. It consists of the heart and blood vessels. The vessels leaving the heart are called arteries, vessels that bring blood to the heart - veins. The heart of the fish is two-chambered. It consists of atria And ventricle, the muscular walls of which alternately contract. From the atrium, blood is pushed into the ventricle, and from it into a large artery - abdominal aorta. Valves prevent blood from flowing back. The abdominal aorta goes to gills, in them the blood is dark in color, saturated with carbon dioxide and is called venous. In the gills the vessels branch into capillaries. The blood flowing in them is freed from carbon dioxide and saturated with oxygen. In the vessels extending from the gills, a scarlet, saturated with oxygen flows. rterial blood. She's going to dorsal aorta, which stretches along the body under the spine. In the caudal region, the dorsal aorta passes through the lower vertebral arches.

From the dorsal aorta branch smaller arteries that branch in various organs to capillaries. Through the walls of these capillaries, oxygen and nutrients enter the tissues, and from them carbon dioxide and other waste products enter the blood.

Gradually, the scarlet arterial blood darkens and turns into venous blood, containing a lot of carbon dioxide and little oxygen. Venous blood collects in the veins and flows through them into the atrium. Thus, the blood continuously circulates one at a time closed circle of blood circulation.

Excretory system of fish using the example of river perch

In the upper part of the body cavity lie two ribbon-shaped red-brown kidneys. In the capillaries of the kidneys, waste products are filtered from the blood, forming urine. It passes through two ureters to bladder, opening outwards behind anus.

Metabolism of fish

In the body of a fish, like all other living organisms, processes take place that ensure their growth, vital activity, reproduction, constant contact and exchange with the external environment. The combination of all these processes is called the metabolism of living organisms.

Nervous system of fish

Figure: Internal structure of river perch. Nervous system

Fish spinal cord

The central nervous system of fish, like that of the lancelet, has the shape of a tube. Her posterior region is spinal cord located in the spinal canal formed by the upper bodies and arches of the vertebrae. From the spinal cord between each pair of vertebrae, nerves extend to the right and left that control the functioning of the muscles of the body and fins and organs located in the body cavity.

Signals of irritation are sent along nerves from sensory cells on the fish’s body to the spinal cord.

Fish brain

The anterior part of the neural tube of fish and other vertebrates is modified into brain, protected by the bones of the skull. The vertebrate brain has different divisions: forebrain, diencephalon, midbrain, cerebellum And medulla. All parts of the brain are of great importance in the life of a fish. For example, the cerebellum controls the animal's coordination and balance. The medulla oblongata gradually passes into the spinal cord. It plays a large role in controlling breathing, blood circulation, digestion and other essential functions of the body.

Sense organs of fish using the example of river perch

Sense organs allow fish to navigate their environment well. An important role is played in this eyes. Perch sees only at a relatively close distance, but distinguishes the shape and color of objects.

Two holes are placed in front of each eye of the perch - nostrils, leading to a blind sac with sensitive cells. This is the organ of smell.

Hearing organs of river perch

Hearing organs They are not visible from the outside, they are placed on the right and left of the skull, in the bones of the back part. Due to the density of water, sound waves are well transmitted through the bones of the skull and are perceived by the hearing organs of the fish. Experiments have shown that fish can hear the footsteps of a person walking along the shore, the ringing of a bell, or a gunshot.

Taste organs of river perch

The taste organs are sensitive cells. They are located in perch, like other fish, not only in the oral cavity, but also scattered over the entire surface of the body. There are also tactile cells there. Some fish (for example, catfish, carp, cod) have tactile antennae on their heads.

Side line

Fish are characterized by a special sensory organ - the lateral line. A series of holes are visible on the outside of the body. These holes are connected to a channel located in the skin. The canal contains sensory cells connected to a nerve running under the skin.

The lateral line perceives the direction and strength of water flow. Thanks to the lateral line, even blinded fish do not bump into obstacles and are able to catch moving prey.

Reflexes of fish using the example of river perch

Observing the behavior of a perch in an aquarium, you can notice that its responses to irritation can manifest themselves in two ways.

If you touch the perch, it will instantly dart to the side. His response to the type of food is just as quick. A greedy predator, it quickly rushes at its prey (small fish and various invertebrates - crustaceans, worms). At the sight of prey, excitation goes along the optic nerve to the central nervous system of the perch and immediately returns from it through the motor nerves to the muscles. The perch swims to the prey and captures it. The mechanism of such body responses to irritation is innate - such reflexes called, as you already know, congenital or unconditional. All animals of the same species have the same unconditioned reflexes. They are inherited.

If feeding fish in an aquarium is accompanied by any actions (conditions), for example, lighting a light bulb or tapping on glass, then after a while such a signal begins to attract fish on its own, without feeding. In response to such signals, fish produce acquired, or conditional reflexes, arising under certain conditions.

Unlike innate reflexes, conditioned reflexes are not inherited. They are individual and are produced during the life of the animal.