Adaptation of the internal structure of fish to their habitat. Arseny Knyazkov "Fish World"

Deep sea fish are considered one of the most amazing creatures on the planet. Their uniqueness is explained primarily by the harsh living conditions. That is why the depths of the world's oceans, and especially deep-sea depressions and trenches, are not at all densely populated.

and their adaptation to living conditions

As already mentioned, the depths of the oceans are not as densely populated as, say, the upper layers of water. And there are reasons for this. The fact is that the conditions of existence change with depth, which means that organisms must have some adaptations.

1. Life in the dark. With depth, the amount of light decreases sharply. It is believed that the maximum distance a sunbeam travels in water is 1000 meters. Below this level, no traces of light were detected. Therefore, deep-sea fish are adapted to life in complete darkness. Some species of fish do not have functioning eyes at all. The eyes of other representatives, on the contrary, are very developed, which makes it possible to capture even the weakest light waves. Another interesting adaptation is luminescent organs that can glow using energy chemical reactions. Such light not only facilitates movement, but also lures potential prey.
2. High pressure. Another feature of deep-sea existence. That is why the internal pressure of such fish is much higher than that of their shallow-water relatives.
3. Low temperature. With depth, the water temperature decreases significantly, so fish are adapted to life in such an environment.
4. Lack of food. Since the diversity of species and the number of organisms decreases with depth, there is, accordingly, very little food left. Therefore, deep-sea fish have supersensitive organs of hearing and touch. This gives them the ability to detect potential prey over long distances, which in some cases can be measured in kilometers. By the way, such a device makes it possible to quickly hide from a larger predator.

You can see that fish living in the depths of the ocean are truly unique organisms. In fact, a huge area of ​​the world's oceans still remains unexplored. That is why the exact number of deep-sea fish species is unknown.

Diversity of fish living in water depths

Although modern scientists know only a small part of the population of the deep, there is information about some very exotic inhabitants of the ocean.

Bathysaurus- the deepest-sea predator fish, living at depths from 600 to 3500 m. They live in tropical and subtropical waters. This fish has almost transparent skin, large, well-developed sensory organs, and its mouth cavity is lined with sharp teeth(even the tissues of the palate and tongue). Representatives of this species are hermaphrodites.

Viper fish- another unique representative of the underwater depths. It lives at a depth of 2800 meters. It is these species that populate the depths. The main feature of the animal is its huge fangs, which are somewhat reminiscent of the poisonous teeth of snakes. This species is adapted to existence without constant food - the fish’s stomachs are so stretched that they can swallow whole Living being much larger than themselves. And on the tail, fish have a specific luminous organ, with the help of which they lure out prey.

Angler- a rather unpleasant-looking creature with huge jaws, small body and poorly developed muscles. Lives on Since this fish cannot actively hunt, it has developed special adaptations. has a special luminous organ that releases certain chemicals. Potential prey reacts to light, swims up, after which the predator swallows it completely.

In fact, there are much more depths, but not much is known about their lifestyle. The fact is that most of them can exist only under certain conditions, in particular, when high blood pressure. Therefore, it is not possible to extract and study them - when they rise to the upper layers of water, they simply die.

With all the diversity of fish, they all have a very similar external body structure, since they live in the same environment - aquatic. This medium is characterized by certain physical properties: high density, the action of the Archimedean force on objects immersed in it, illumination only in the uppermost layers, temperature stability, oxygen only in a dissolved state and in small quantities.

The BODY FORM of fish is such that it has maximum hydrodynamic properties that make it possible to overcome water resistance to the greatest extent. The efficiency and speed of movement in water is achieved by the following features of the external structure:

Streamlined body: pointed front part of the body; there are no sharp transitions between the head, body and tail; there are no long branched outgrowths of the body;

Smooth skin covered with small scales and mucus; the free edges of the scales are directed backward;

The presence of fins with a wide surface; of which two pairs of fins - chest and abdominal - real limbs.

RESPIRATORY SYSTEM - gills having large area gas exchange. Gas exchange in the gills is carried out by diffusion of oxygen and carbon dioxide gas between water and blood. It is known that in an aquatic environment the diffusion of oxygen is approximately 10,000 times slower than in air. Therefore, fish gills are designed and work to increase the efficiency of diffusion. Diffusion efficiency is achieved in the following way:

Gills have a very large area of ​​gas exchange (diffusion), due to the large number gill filaments on each gill arch ; every

the gill filament, in turn, is branched into many gill plates; good swimmers have a gas exchange area 10 - 15 times larger embroiders the surface of the body;

The gill plates are very thin-walled, about 10 microns thick;

Each gill plate contains a large number of capillaries, the wall of which is formed by only one layer of cells; the thinness of the walls of the gill plates and capillaries determines the short path of oxygen diffusion and carbon dioxide;

A large amount of water is pumped through the gills due to the work of " gill pump"in bony fishes and ram ventilation- special breathing method in which the fish swims with its mouth open and gill cover; ram ventilation - predominant mode of respiration in cartilaginous fish ;

Principle counterflow: direction of water movement through the gills the plates and the direction of blood movement in the capillaries are opposite, which increases the completeness of gas exchange;

Fish blood contains hemoglobin in its red blood cells, which is why blood absorbs oxygen 10 to 20 times more efficiently than water.

The efficiency of fish extracting oxygen from water is much higher than that of mammals from the air. Fish extract 80-90% of dissolved oxygen from water, and mammals extract only 20-25% of oxygen from inhaled air.

Fish living in conditions of constant or seasonal lack of oxygen in water can use oxygen from the air. Many species simply swallow the air bubble. This bubble is either retained in the mouth or swallowed. For example, carp have highly developed capillary networks in the oral cavity, which receive oxygen from the bladder. The swallowed bubble passes through the intestine, and from it oxygen enters the capillaries of the intestinal wall (in loaches, loaches, crucian carp). Famous group labyrinth fish, which have a system of folds (labyrinth) in the oral cavity. The walls of the labyrinth are abundantly supplied with capillaries, through which oxygen enters the blood from a swallowed air bubble.

Lungfish and lobe-finned fish have one or two lungs , developing as a protrusion of the esophagus, and nostrils, allowing air to be inhaled when closed mouth. Air enters the lung and through its walls into the blood.

Interesting features of gas exchange in Antarctic icy, or white-blooded fish that do not have red blood cells and hemoglobin in the blood. They effectively diffuse through the skin, because the skin and fins are abundantly supplied with capillaries. Their heart is three times heavier than that of close relatives. These fish live in Antarctic waters, where the water temperature is about -2 o C. At this temperature, the solubility of oxygen is much higher than in warm water.

The swim bladder is a special organ of bony fish that allows you to change the density of the body and thereby regulate the depth of immersion.

BODY COLOR largely makes the fish invisible in the water: along the back the skin is darker, the ventral side is light and silvery. From above the fish is invisible against the background of dark water, from below it merges with the silvery surface of the water.

Living conditions in various areas of fresh water, especially in the sea, leave a sharp mark on the fish living in these areas.
Fishes can be divided into marine fish, anadromous fish, semi-anadromous fish, or estuarine fish, brackish water fish, and freshwater fish. Significant differences in salinity already have implications for the distribution of individual species. The same is true for differences in other properties of water: temperature, lighting, depth, etc. Trout requires different water than barbel or carp; Tench and crucian carp also live in reservoirs where perch cannot live because the water is too warm and muddy; asp requires clean, flowing water with fast riffles, and pike can also stay in standing water overgrown with grass. Our lakes, depending on the conditions of existence in them, can be distinguished as pike-perch, bream, crucian carp, etc. Inside, more or less large lakes and rivers we can mark different zones: coastal, open water and bottom, characterized different fish. Fish from one zone can enter another zone, but in each zone one or another predominates. species composition. The coastal zone is the richest. The abundance of vegetation, therefore food, makes this area favorable for many fish; This is where they feed, this is where they spawn. The distribution of fish among zones plays a big role in fishing. For example, burbot (Lota lota) is a demersal fish, and is caught from the bottom with nets, but not with floating nets, which are used to catch asp, etc. Most whitefish (Coregonus) feed on small planktonic organisms, mainly crustaceans. Therefore, their habitat depends on the movement of plankton. In winter, they follow the latter into the depths, but in the spring they rise to the surface. In Switzerland, biologists indicated places where planktonic crustaceans live in winter, and here the whitefish fishery arose; On Baikal, omul (Coregonus migratorius) is caught in winter nets at a depth of 400-600 m.
The demarcation of zones in the sea is more pronounced. The sea, according to the living conditions it provides for organisms, can be divided into three zones: 1) littoral, or coastal; 2) pelagic, or zone open sea; 3) abyssal, or deep. The so-called sublittoral zone, which constitutes the transition from coastal to deep, already displays all the signs of the latter. Their boundary is a depth of 360 m. The coastal zone begins from the shore and extends to a vertical plane delimiting the area deeper than 350 m. The open sea zone will be outward from this plane and upward from another plane lying horizontally at a depth of 350 m. The deep zone will be below from this last one (Fig. 186).

Light is of great importance for all life. Since water transmits the rays of the sun poorly, conditions of existence that are unfavorable for life are created in water at a certain depth. Based on the intensity of illumination, three light zones are distinguished, as indicated above: euphotic, disphotic and aphotic.
Free-swimming and bottom-dwelling forms are closely mixed along the coast. Here is the cradle of marine animals, from here come the clumsy inhabitants of the bottom and the agile swimmers of the open sea. Thus, off the coast we will find a fairly diverse mixture of types. But living conditions in the open sea and at depths are very different, and the types of animals, in particular fish, in these zones are very different from each other. We call all animals that live on the bottom of the sea by one name: benthos. This includes bottom-crawling, bottom-lying, burrowing forms (mobile benthos) and sessile forms (sessile benthos: corals, sea anemones, tube worms, etc.).
We call those organisms that can swim freely pecton. The third group of organisms, devoid or almost devoid of the ability to move actively, clinging to algae or helplessly carried by the wind or currents, is called planktol. Among fish we have forms belonging to all three groups of organisms.
Nonlagic fishes - nekton and plankton. Organisms that live in water independently of the bottom and are not connected to it are called nonlagic. This group includes organisms both living on the surface of the sea and in its deeper layers; organisms that actively swim (nekton) and organisms carried by wind and currents (plankton). Deep-living pelagic animals are called bathinelagic.
Living conditions in the open sea are characterized primarily by the fact that there is no surf here, and animals do not need to develop adaptations for staying on the bottom. There is nowhere for a predator to hide, lying in wait for its prey, and the latter has nowhere to hide from predators. Both must rely mainly on their own speed. Most open sea fish are therefore excellent swimmers. This is the first thing; secondly, coloring sea ​​water, blue in both transmitted and incident light affects the color of pelagic organisms in general and fish in particular.
The adaptations of nekton fish to movement vary. We can distinguish several types of nektonic fish.
In all these types, the ability to swim quickly is achieved in different ways.
The type is spindle-shaped, or torpedo-shaped. The organ of movement is the caudal section of the body. An example of this type would be: porbeagle(Lamna cornubica), mackerel (Scomber scomber), salmon (Salmo salar), herring (Clupea harengus), cod (Gadus morrhua).
Ribbon type. The movements occur with the help of serpentine movements of a laterally compressed, long ribbon-like body. For the most part, they are inhabitants of rather great depths. Example: kingfish, or strapfish (Regalecus banksii).
Arrow-shaped type. The body is elongated, the snout is pointed, strong unpaired fins are set back and arranged in the form of an arrow, forming one piece with the caudal fin. Example: common garfish (Belone belone).
Sail type. The snout is elongated, unpaired fins and general form like the previous one, front dorsal greatly enlarged and can serve as a sail. Example: sailfish (Histiophorus gladius, Fig. 187). The swordfish (Xiphias gladius) also belongs here.

Fish is essentially an animal that actively swims; therefore, there are no real planktonic forms among them. We can distinguish the following types of fish approaching the plankton.
Needle type. Active movements are weakened, performed with the help of quick bends of the body or undulating movements of the dorsal and anal fins. Example: pelagic pipefish (Syngnathus pelagicus) of the Sargasso Sea.
The type is compressed-symmetrical. The body is tall. The dorsal and anal fins are located opposite each other and are high. Pelvic fins are mostly absent. Movement is very limited. Example: sunfish (Mola mola). This fish also lacks a caudal fin.
He does not make active movements, the muscles are largely atrophied.
Spherical type. The body is spherical. The body of some fish can inflate due to swallowing air. Example: hedgehog fish (Diodon) or deep-sea melanocetus (Melanocetus) (Fig. 188).

There are no true planktonic forms among adult fish. But they are found among planktonic eggs and larvae of fish leading a planktonic lifestyle. The body's ability to float depends on a number of factors. First of all, the specific gravity of water is important. An organism floats on water, according to Archimedes' law, if its specific gravity is not greater than the specific gravity of water. If the specific gravity is greater, then the organism sinks at a rate proportional to the difference in specific gravity. The rate of descent, however, will not always be the same. (Small grains of sand sink more slowly than large stones of the same specific gravity.)
This phenomenon depends, on the one hand, on the so-called viscosity of water, or internal friction, and on the other, on what is called the surface friction of bodies. The larger the surface of an object in comparison with its volume, the greater its surface resistance, and it sinks more slowly. The low specific gravity and high viscosity of water prevent immersion. Excellent examples of such a change are, as we know, copepods and radiolarians. In eggs and larvae of fish we observe the same phenomenon.
Pelagic eggs are mostly small. The eggs of many pelagic fish are equipped with thread-like outgrowths that prevent them from diving, for example, the eggs of mackerel (Scombresox) (Fig. 189). The larvae of some fish leading a pelagic lifestyle have adaptations for staying on the surface of the water in the form of long threads, outgrowths, etc. These are the pelagic larvae of the deep-sea fish Trachypterus. In addition, the epithelium of these larvae is changed in a very unique way: its cells are almost devoid of protoplasm and are stretched to enormous sizes by liquid, which, of course, reducing the specific gravity, also helps to keep the larvae on the water.

Another condition affects the ability of organisms to float on water: osmotic pressure, which depends on temperature and salinity. With a high salt content in the cell, the latter absorbs water, and although it becomes heavier, its specific gravity decreases. Getting into more salt water, the cell, on the contrary, having decreased in volume, will become heavier. Pelagic eggs of many fish contain up to 90% water. Chemical analysis has shown that in the eggs of many fish the amount of water decreases with the development of the larva. As water becomes depleted, the developing larvae sink deeper and deeper and finally settle to the bottom. The transparency and lightness of cod larvae (Gadus) are determined by the presence of a vast subcutaneous space filled with watery fluid and stretching from the head and yolk sac to the posterior end of the body. The same vast space is found in the eel larva (Anguilla) between the skin and muscles. All these devices undoubtedly reduce weight and prevent immersion. However, even with a large specific gravity, an organism will float on water if it presents sufficient surface resistance. This is achieved, as stated, by increasing volume and changing shape.
Deposits of fat and oil in the body, serving as a food reserve, at the same time reduce its specific gravity. The eggs and juveniles of many fish exhibit this adaptation. Pelagic eggs do not stick to objects, they swim freely; many of them contain a large drop of fat on the surface of the yolk. These are the eggs of many cod fish: the common cod (Brosmius brosme), often found on Murman; Molva molva, which is caught there; These are the eggs of mackerel (Scomber scomber) and other fish.
All kinds of air bubbles serve the same purpose - to reduce the specific gravity. This includes, of course, the swim bladder.
Eggs are built according to a completely different type, submersible - demersal, developing at the bottom. They are larger, heavier, and darker, while pelagic eggs are transparent. Their shell is often sticky, so these eggs stick to rocks, seaweed and other objects, or to each other. In some fish, like the garfish (Belone belonе), the eggs are also equipped with numerous thread-like outgrowths that serve to attach to algae and to each other. In smelt (Osmerus eperlanus), eggs are attached to stones and rocks using the outer shell of the egg, which is separated, but not completely, from the inner membrane. Large eggs of sharks and rays also stick. The eggs of some fish, such as salmon (Salmo salar), are large, separate and do not stick to anything.
Bottom fish, or benthic fish. Fish that live near the bottom near the coast, as well as pelagic fish, represent several types of adaptation to their living conditions. Their main conditions are as follows: firstly, constant danger to be thrown ashore by the surf or in a storm. Hence the need to develop the ability to hold on to the bottom. Secondly, the danger of being broken on rocks; hence the need to purchase armor. Fish that live on the muddy bottom and burrow in it develop various adaptations: some for digging and moving into the mud, and others for catching prey by burrowing in the mud. Some fish have adaptations for hiding among algae and corals growing among the shores and on the bottom, while others have adaptations for burying in the sand at low tide.
We distinguish the following types of bottom fish.
Type flattened dorsoventrally. The body is compressed from the dorsal to the ventral side. The eyes are moved to the upper side. The fish may press closely to the bottom. Example: stingrays (Raja, Trygon, etc.), and among bony fish - sea devil (Lophius piscatorius).
Longtail type. The body is strongly elongated, the highest part of the body is behind the head, gradually becoming thinner and ending in a point. The apal and dorsal fins form a long fin edge. The type is common among deep-sea fish. Example: Longtail (Macrurus norvegicus) (Fig. 190).
The type is compressed-asymmetric. The body is compressed laterally, bordered by long dorsal and anal fins. Eyes on one side of the body. In youth they have a compressed-symmetrical body. There is no swim bladder, they stay at the bottom. This includes the flounder family (Pleuronectidae). Example: turbot (Rhombus maximus).

Eel type. The body is very long, serpentine; paired fins are rudimentary or absent. Bottom fish. Movement along the bottom created the same shape that we see among reptiles in snakes. Examples include the eel (Anguilla anguilla), lamprey (Petromyzon fluviatilis).
Type asterolepiform. The front half of the body is enclosed in a bony armor, which reduces active movements to a minimum. The body is triangular in section. Example: boxfish (Ostracion cornutus).
Special conditions prevail at great depths: enormous pressure, absolute absence of light, low temperature (up to 2°), complete calm and lack of movement in the water (except for the very slow movement of the entire mass of water from the Arctic seas to the equator), absence of plants. These conditions leave a strong imprint on the organization of fish, creating a special character for the deep fauna. Their muscular system is poorly developed, their bones are soft. The eyes are sometimes reduced to the point of complete disappearance. In those deep-deep fish that retain eyes, the retina, in the absence of cones and the position of the pigment, is similar to the eye of nocturnal animals. Further, deep fish differ big head and a thin body, thinning towards the end (long-tailed type), a large extensible stomach and very large teeth in the mouth (Fig. 191).

Deep fishes can be divided into benthic and bathypelagic fishes. The bottom-dwelling fish of the depths include representatives of stingrays (Turpedinidae family), flounder (Pleuronectidae family), handfin (Pediculati family), cataphracti (Cataphracti), longtail (Macruridae family), eelpout (Zoarcidae family), cod (Family Gadidae) and others. However, representatives of the named families are found both among bathypelagic and coastal fish. Drawing a sharp, distinct boundary between deep-seated forms and coastal ones is not always easy. Many forms are found here and there. Also, the depth at which bathypelagic forms are found varies widely. Of the bathypelagic fishes, luminous anchovies (Scopelidae) should be mentioned.
Bottom fish feed on sedentary animals and their remains; this does not require any effort, and bottom-dwelling fish usually stay in large schools. On the contrary, bathypelagic fish find their food with difficulty and stay alone.
Most commercial fish belong to either littoral or pelagic fauna. Some cod (Gadidae), mullet (Mugilidae), flounders (Pleuronectidae) belong to coastal zone; tuna (Thynnus), mackerel (Scombridae) and main commercial fish- herrings (Clupeidae) - belong to the pelagic fauna.
Of course, not all fish necessarily belong to one of these types. Many fish only approach one or another of them. Bright expressed type structures are the result of adaptation to certain, strictly isolated conditions of habitat and movement. But such conditions are not always well expressed. On the other hand, in order for one type or another to develop, it is necessary for a long time. A fish that has recently changed its habitat may lose part of its previous adaptive type, but not yet develop a new one.
Fresh water does not have the diversity of living conditions that is observed in the sea, however, even among freshwater fish There are several types. For example, dace (Leuciscus leuciscus), which prefers to stay in a more or less strong current, has a type approaching fusiform. On the contrary, bream (Abramis brama) or crucian carp (Carassius carassius), belonging to the same family of carp (Cyprinidac) - sedentary fish that live among aquatic plants, roots and under steep rocks - have a clumsy body, compressed from the sides, like reef fish. The pike (Esox lucius), a swiftly attacking predator, resembles an arrow-shaped type of nektonic fish; Living in mud and mud, the loach (Misgurnus fossilis), a reptile near the bottom, has a more or less eel-like shape. The sterlet (Acipenser ruthenus), which constantly creeps along the bottom, resembles a type of longtail.

Open biology lesson in 7th grade

Topic: “Pisces superclass. Adaptations of fish to aquatic habitats"

Goal: To reveal the features of the internal and external structure of fish in connection with their habitat, to show the diversity of fish, to determine the significance of fish in nature and economic activity people, indicate the necessary measures to protect fish resources.

Methodological goal: the use of ICT as one of the ways to form creative thinking and development of student interest, expansion of research experience based on previously acquired knowledge, development of information and communication competencies.

Lesson type: combined.

Type of lesson: lesson in the formation and systematization of knowledge.

Lesson objectives:

Educational: generate knowledge about general characteristics fish, features of the external structure of fish in connection with the aquatic habitat.

Educational: develop the ability to observe, establish cause-and-effect relationships, continue to develop the ability to work with a textbook: find answers to questions in the text, use the text and pictures to complete independent work.

Educational: fostering hard work, independence and respect when working in pairs and groups.

Objectives: 1) To familiarize students with the structural features of fish.

2) Continue developing the skills to observe the living

Organisms, work with the textbook text, perceive

Educational information through multimedia presentation and video.

Equipment: computer, multimedia projector,

Lesson plan:

Organizing time

Arousing interest

Setting goals.

Learning a new topic

Operational-cognitive

Reflection

During the classes

Lesson steps

Teacher activities

Student activities

1. Organizational.

2 minutes

Greets students, checks that the workplace is ready for class, and creates a favorable, relaxed environment.

Divides into groups

Greeting teachers, checking availability didactic materials

to work for class.

Divided into groups

2. Arouse interest

3 min

Game “Black Box”

1. There is information that these animals were bred in ancient Egypt more than four thousand years ago. In Mesopotamia they were kept in ponds.

Kept in Ancient Rome and Greece.

They first appeared in Europe only in the 17th century.

They first came to Russia from China as a gift to Tsar Alexei Mikhailovich. The king ordered them to be planted in crystal thickets.

IN good conditions content can live up to 50 years.

Fairy-tale character who makes wishes come true.

2. There is such a zodiac sign

Teacher: -So who will we meet in class today?

Students offer answers after each question.

Pupils: - goldfish.

And they set the topic of the lesson.

3.Setting goals

Goal: to activate cognitive interest to the topic being studied.

1) Let's get acquainted with the structural features of fish.

2) We will continue to develop the skills to observe living organisms, work with textbook text, perceive

1) Study the structural features of fish.

2) They will work with the text of the textbook, perceive

educational information through multimedia presentation.

4. Studying a new topic.

Operational-cognitive.

Purpose: using various shapes and working methods to form knowledge about the external and internal structure of fish

15 minutes

Guys, today we will get acquainted with the most ancient vertebrates. Superclass of fish. This is the most numerous class of Chordates. There are about 20 thousand species. The branch of Zoology that studies fish is called ICHTHYOLOGY.

Stage I – Challenge (motivation).

Teacher: Sometimes they say about a person: “He feels like a fish in water.” How do you understand this expression?

Teacher: Why do fish feel good in water?

Teacher: How is the adaptation of fish to the aquatic environment expressed? We will learn this during today's lesson.

Stage II – maintenance.

What Features of the Aquatic Habitat can we name:

1 task. Watch the video fragment.

Using the textbook and additional text, using the Fishbone technique, describe the adaptation of fish to living in an aquatic environment.

Listening

Expected answers from students (it means he feels good, comfortable, everything works out for him).

(It is adapted to life in water).

The children write down the topic of the lesson in their notebook.

The high density of water makes active movement difficult.

Light penetrates water only to a shallow depth.

Limited quantity oxygen.

Water is a solvent (salts, gases).

Thermal water (temperature conditions are milder than on land).

Transparency. Fluidity.

Conclusion : the fish’s adaptability to life in water is manifested in the streamlined shape of the body, smoothly transitioning body organs, protective coloring, features of the integument (scales, mucus), sensory organs (lateral line), and locomotor organs (fins).

- What is the body shape of a fish and how is it adapted to its environment?

Teacher's addition.Man arranges for his movement in water by sharpening the bows of his boats and ships, and when building submarines he gives them a spindle-shaped, streamlined shape of a fish body). The body shape can be different: spherical (hedgehog fish), flat (stingray, flounder), serpentine (eels, moray eels).

What are the features of the body cover of a fish?

What is the significance of the slimy film on the surface of fish?

Teacher's addition. This mucous film helps reduce friction when swimming, and due to its bactericidal properties, prevents bacteria from penetrating the skin, because fish skin is permeable to water and some substances dissolved in it (fear hormone)

WHAT IS “THE STUFF OF FEAR”
In 1941 Nobel laureate Karl von Frisch, studying the behavior of fish, discovered that when a pike grabs a minnow, some substance gets into the water from wounds on its skin, which causes a fear reaction in other minnows: they first rush in all directions, and then They gather in a dense flock and stop feeding for a while.

In modern scientific literature, instead of the phrase “fear substance,” you can often find the term “anxiety pheromone.” In general, pheromones are substances that, when released into the external environment by one individual, cause some specific behavioral reaction in other individuals.

In fish, the alarm pheromone is stored in special cells located in the very top layer skin. They are very numerous and in some fish they can occupy more than 25% of the total skin volume. These cells have no connections with external environment, so their contents can get into the water only in one case - if the fish’s skin gets damaged in some way.
The largest numbers of alarm pheromone cells are concentrated on the front part of the fish’s body, including the head. The further back, towards the tail part of the body, the fewer cells with pheromone.

What are the coloring features of fish?

Bottom fish and fish of grassy and coral thickets often have a bright spotted or striped color (the so-called “dismembering” coloring masking the contours of the head). Fish can change their color depending on the color of the substrate.

What is a lateral line and what is its significance?

Drawing up a general Fishbone at the board .

The fish swims in the water quickly and nimbly; it easily cuts through water due to the fact that its body has a streamlined shape (in the form of a spindle), more or less compressed from the sides.

Reduced water friction

The body of fish is mostly covered with hard and dense scales, which sit in folds of the skin (how are our nails? , and their free ends overlap each other, like tiles on a roof. The scales grow along with the growth of the fish, and in the light we can see concentric lines reminiscent of growth rings on sections of wood. By the growths of concentric stripes, one can determine the age of the scales, and at the same time the age of the fish itself. Additionally, the scales are covered with mucus.

Body coloring. The fish has a dark back and a light belly. The dark coloring of the back makes them hardly noticeable against the background of the bottom when viewed from above; the shiny silver coloring of the sides and belly makes the fish invisible against the background of a light sky or sun glare when viewed from below.

The coloring makes the fish inconspicuous against the background of its habitat.

Side line. With its help, fish navigate water flows, perceive the approach and departure of prey, predators or school partners, and avoid collisions with underwater obstacles.

PHYS. JUST A MINUTE

Goal: maintaining health.

3 min

Doing exercises.

12 min

What other adaptations do fish have for living in water?

To do this, you will work in small groups. You have additional material on your tables. You must read the text material, answer the questions and indicate the structural features of the fish in the picture.

Gives assignments to each group:

"1. Read the text.

2. Look at the drawing.

3. Answer the questions.

4. Indicate the structural features of the fish in the drawing.”

Group 1. Locomotion organs of fish.

2. How do they work?

Group 2. Respiratory system of fish.

Group 3. Sense organs of fish.

1. What sense organs do fish have?

2. Why are sense organs needed?

Students organize the search and exchange of ideas through dialogue.Work is being organized to fill out the drawing.

4. Reflective-evaluative.

Purpose: determining the level of knowledge acquired in the lesson.

7 min

Quest "Fishing"

1. What parts does the body of a fish consist of?

2. With the help of what organ does a fish perceive the flow of water?

3. What structural features of a fish help it overcome water resistance?

4. Does the fish have a passport?

5. Where is the fear substance found in fish?

6. Why do many fish have a light belly and a dark back?

7. What is the name of the branch of zoology that studies fish?

8. Why do flounder and stingray have a flat body shape?

9. Why can't fish breathe on land?

10. What sense organs do fish have?

11. Which fish fins are paired? Which fish fins are not paired?

12. What fins do fish use as oars?

Each team chooses a fish and answers questions.

3 min

A drawing of a fish is hung on the board. The teacher offers to evaluate today’s lesson, what new things you learned, etc.

1. Today I found out...

2. It was interesting...

3. It was difficult...

4. I learned...

5. I was surprised...

6. I wanted...

On multi-colored stickers, children write what they liked most in the lesson, what new things they learned and stick them on the fish in the form of scales.

5. Homework.

Describe the internal structure of a fish.

Make a crossword puzzle.

Write down homework in a diary.

Group 1. The musculoskeletal system of fish.

1. What organs are the organs of movement of fish?

2. How do they work?

3. What groups can they be divided into?

Fin - this is a special organ necessary for coordinating and controlling the process of fish movement in water. Each fin consists of a thin leathery membrane, whichWhen the fin straightens, it stretches between the bony fin rays and thereby increases the surface of the fin itself.

Number of fins various types can be different, and the fins themselves can be paired or unpaired.

In river perch, unpaired fins are located on the back (there are 2 of them - large and small), on the tail (large two-lobed caudal fin) and on the underside of the body (the so-called anal fin).

The pectoral fins (the front pair of limbs) and the ventral fins (the back pair of limbs) are paired.

The caudal fin plays an important role in the process of moving forward, the paired fins are necessary for turning, stopping and maintaining balance, the dorsal and anal fins help the perch maintain balance while moving and during sharp turns.

Group 2.Respiratory system of fish.

Read the text. Look at the drawing. Answer the questions.

Indicate the structural features of the fish in the picture.

1. What organs make up the respiratory system of fish?

2. What structure do gills have?

3. How does fish breathe? Why can't fish breathe on land?

The main respiratory organ of fish is the gills. The inert base of the gill is the gill arch.

Gas exchange occurs in the gill filaments, which have many capillaries.

The gill rakers “strain” the incoming water.

The gills have 3-4 gill arches. Each arch has bright red stripes on one side.gill filaments , and on the other - gill rakers . The gills are covered on the outsidegill covers . Visible between the arcsgill slits, which lead to the pharynx. From the pharynx, captured by the mouth, water washes the gills. When a fish presses its gill covers, water flows through the mouth to the gill slits. Oxygen dissolved in water enters the blood. When a fish lifts its gill covers, water is pushed out through the gill slits. Carbon dioxide leaves the blood into the water.

Fish cannot stay on land because the gill plates stick together and air does not enter the gill slits.

Group 3.Sense organs of fish.

Read the text. Look at the drawing. Answer the questions.

Indicate the structural features of the fish in the picture.

1. What organs make up the nervous system of a fish?

2. What sense organs do fish have?

3. Why are sense organs needed?

The fish has sense organs that allow fish to navigate their environment well.

1. Vision - eyes - distinguishes the shape and color of objects

2. Hearing - the inner ear - hears the steps of a person walking along the shore, the ringing of a bell, a shot.

3. Smell - nostrils

4. Touch - antennae.

5. Taste – sensitive cells – throughout the entire surface of the body.

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

On the sides of the body, a lateral line is visible in the scales - a kind of organfeelings in fish. It is a channel that lies in the skin and has many receptors that perceive the pressure and force of water flow, electromagnetic fields of living organisms, as well as stationary objects due to wavesdeparting from them. Therefore, in muddy water and even in complete darkness, fish are perfectly oriented and do not stumble upon underwater objects. In addition to the lateral line organ, fish have sensory organs located on the head. In front of the head there is a mouth, with which the fish captures food and draws in water necessary for breathing. Located above the mouthnostrils are the olfactory organ through which fish perceive the odors of substances dissolved in water. On the sides of the head there are eyes, quite large with a flat surface - the cornea. The lens is hidden behind it. Pisces seeat close range and distinguish colors well. Ears are not visible on the surface of the fish's head, but this does not mean thatfish don't hear. They have an inner ear in their skull that allows them to hear sounds. Nearby is a balance organ, thanks to which the fish senses the position of its body and does not roll over.

Section 1. Swimming devices.

There are many difficulties in swimming. For example, in order not to drown, a person must constantly move or at least make an effort. But how does the most common river pike hang in the water and not drown? Carry out the experiment: take a thin, light stick and pass it in the air. Not difficult? Try it in water. It's more difficult, isn't it? But fish are always moving in the water, and nothing! These are the questions that will be explained in this section.
The first question is why fish don't drown. Yes, because they have a swim bladder - a modified lung filled with gas, fat or some other filler that provides buoyancy to the fish’s body. It is located under the spine, supporting it as the heaviest element of the body. Cartilaginous animals do not have this bladder, so sharks and chimeras are forced to move most of the time. Only some sharks have primitive bladder substitutes. Previously, it was believed that sharks would not be able to breathe if they stopped, but this is not so - sharks are not averse to lying at the bottom of the grotto and, which is possible, even sleeping (although it is possible that only exhausted or sick individuals “rest” in the grottoes). Only stingrays do not care about the lack of a swim bladder - they, lazy people, love to lie on the bottom. As for teleosts, only a few species do not have a swim bladder, including the bladderless perches of the scorpionfish family, all representatives of the flounder-like and fused-branchiformes. The swim bladder may consist of several chambers (cyprinid).

The second issue is slight movement in the water. Try to take a board or flat plate floating on water, place it on the water and try, without changing position, to “push” it into the water. She will wag and only then give in. Therefore, to solve this issue, nature gave the fish a streamlined shape, that is, the body became pointed from the head, voluminous towards the middle and tapering towards the tail. But the problem has not been completely resolved: water is an incompressible medium. But the fish overcame this: they began to swim in waves, pushing the water first with their heads, then with their bodies, and then with their tails. The discarded water flows down the sides of the fish, pushing the fish forward. And those fish that do not have this shape are scorpionfish, angler, carpet shark, stingray, flounder, etc. - and do not need it: they are bottom fish. Sitting on the bottom all your life, you can do without streamlining. If you need to move, then the stingray, for example, swims, making wave-like movements with its fins (see illustrations).
Let us dwell on the question of fish covers. There are four main types of fish scales and many minor ones, as well as various thorns and prickles. The placoid scale resembles a plate with a tooth; cartilaginous scales are covered with such scales. Ganoid scales, diamond-shaped and covered with a special substance - ganoin - are a sign of some primitive

ray-finned birds, including armored birds. Bone plates up to 10 cm in diameter - bugs - form 5 longitudinal rows on the skin of the sturgeon, this is all that remains of its scales (not that it has scales - it doesn’t even have teeth, only weak teeth in fry). Small plates and individual scales scattered throughout the body can be ignored. Ctenoid scales differ from cycloid scales only in that ctenoid scales have a jagged outer edge, while cycloid scales have a smooth one. These two types are common among most ray-finned animals (including the most primitive ones - like the cycloid-scaled Amya). Ancient lobe-fins were characterized by cosmoid scales, which consisted of four layers: a superficial enamel-like layer, a second layer of spongy-bone layer, a third layer of bone-spongy layer, and a lower layer of dense bone layer. It is preserved in coelacanths; in modern deepnoei, two layers have disappeared. Many fish have spines. Pointed bony plates cover the catfish with a spiny armor. Some fish have poisonous spines (about these fish in the second part of the chapter “Dangerous Fish”). A kind of “brush” of thorns on the back and many thorns covering the head are signs ancient shark Stetacanthus (more details -).
The limbs of fish that help in swimming are fins. Bony fish have a spiny dorsal fin on their back, followed by a soft dorsal fin. Sometimes there is only one dorsal fin. Pectoral fins are located near the gill covers on both sides. At the beginning of the belly, the bony fish has paired ventral fins. The anal fin is located near the urinary and anal openings. The “tail” of a fish is the caudal fin. In cartilaginous fish (sharks) everything is almost the same, only some deviations, but we will not consider them. Modern lampreys and hagfishes have a dorsal fin and a caudal fin.
Now let's talk about what helps fish live in the underwater world.

Section 2. Mimicry of fish.

Mimicry is the ability to blend into the background and be invisible. In this section I will talk about fish mimicry.

Rag picker

In the first (or one of the first) places in terms of mimicry are fish of the order Sticklebacks - seahorses and pipefish. Skates can change color depending on the algae they sit on. Dry yellow algae - and a yellow ridge, green algae - a green ridge, red algae, brown - and the pipit is red or brown. Sea needles do not know how to change color, but they can, when swimming into green algae (the needles themselves are green), imitate them so cleverly that you cannot distinguish them from algae. And one horse - a rag picker - will be saved in the seaweed without hiding. He looks torn and torn all over. If it floats, it is easy to mistake it for a rag or a piece of seaweed. Rag pickers are most diverse off the coast of Australia.
Flounders are no worse at hiding. They are flattened laterally, and both eyes are on the side opposite the sand on which they lie. They are better than skates at camouflaging themselves, taking on almost any color. On sand they are sand-colored, on gray stone they are gray. We even tried placing flounder on a chessboard. And it became black and white checkered!
I talked about the mimicry of scorpionfish and carpet sharks a little earlier. Many fish (for example, the Sargassum clownfish) are camouflaged, like pipefish, under the surrounding algae or corals.
Mimicry of stingrays is very “cunning”. They do not change color or imitate algae. When they lie down on the bottom, they simply cover themselves with a layer of sand! That's all the disguise is.

Section 3. Senses: sixth, seventh...

If you have an aquarium at home, you can conduct a simple experiment. Make each fish a “bathing cap” that fits on the fish’s head (with cutouts for the eyes, mouth, gills and fins). Dip your finger in the water. Did the fish rush away? Now put the “caps” on them and dip them in again

water finger. You will probably be surprised by the abnormal reaction of the fish, who were not at all afraid of an unfamiliar object and even allowed themselves to be touched. It's all about the "sixth sense" of fish, the SIDE LINE system (seismosensory system, or seismosensory sense). A system of channels, called the "lateral line", runs through the entire body of the fish as a series of scales, different from the covering of the entire body, and allows it to perceive all movements of the water. The “cap” blocks the organs of the lateral line of the head, and the fish does not feel the approach of a foreign object. It is the existence of the lateral line that explains why schools of fish instantly change direction as one whole, and no fish moves slower than the others. All bony and cartilaginous fish have a lateral line, with rare exceptions (brachydanios from the carp family), and also, as an inheritance from their fish ancestors, in aquatic amphibians.
But the lateral line organs seemed not enough for the sharks! And they had a “seventh sense”. In the skin of any shark you can find several sacs lined inside, called AMPOULES OF LORENZINI. They open into channels on the head and underside of the sharks' snout. Ampullae of Lorenzini are sensitive to electric fields; they seem to “scan” the bottom of a reservoir and can detect any living creature, even hiding in a secluded place. It is precisely in order to “scan” as much of the bottom as possible with the help of ampoules that the hammerhead fish has such a head shape. In addition, the ampullae of Lorenzini allow sharks to navigate according to the Earth's magnetic field. Of course, rays, descendants of sharks, also have ampoules of Lorenzini.

Section 4. Polar fish, or these amazing nototheniids

Fish that live in some unusual conditions often develop unusual adaptations to them. As an example, I will look at the amazing fish of the suborder Nototheniidae (order Perciformes), living not just anywhere, but in ANTARCTICA.
There are 90 species of notothenaceae found in the seas of the icy continent. Their adaptation to an unfriendly environment began when the continent of Antarctica became such, having separated from Australia and South America. Theoretically, fish can survive when the blood is one degree higher colder than the point, after which freezing begins. But there is ice in Antarctica, and it penetrated through the covers into the blood of the fish and caused the freezing of body fluids even with hypothermia of even 0.1 degrees. Therefore, nototheniid fish began to produce special substances in their blood called ANTIFREEZES, which provide a lower freezing point - they simply do not allow ice crystals to grow. Antifreezes are found in all body fluids, except eye fluid and urine, in almost all nototheniids. Due to this, they freeze at water temperature (at different types) from -1.9 to -2.2 degrees Celsius, whereas ordinary fish- at -0.8 degrees. (The water temperature in, say, McMurdo Sound near Antarctica is from -1.4 to (rarely) -2.15 degrees.)
Notothenia buds are designed in a special way - they excrete exclusively waste from the body, while leaving antifreeze “on duty”. Thanks to this, fish save energy - because they have to produce new “savior substances” less often.
In addition, nototheniids have many more amazing adaptations. For example, in some species the spine is hollow, and in the subcutaneous layer and small deposits among the muscle fibers there are special fats - triglycerides. This promotes buoyancy, which becomes almost neutral (i.e. the specific gravity of the fish is equal to the specific gravity of water, and the fish in its environment is virtually weightless).

Section 5. Tilapia, or some like it hot.

At the end of the chapter, let's move from icy waters Antarctica to the hot springs of Africa and look at the fish that managed to adapt to these difficult conditions. You can find fish while swimming in such a source - a sudden slight tickling probably means that a school of tiny tilapia is interested in you.

During its existence, the water of many African lakes became so saturated with alkalis that fish simply could not live there. The tilapia of lakes Natron and Magadi had to move into the hot waters of the drinking lakes to survive. There they have adapted so much that they die in cool fresh water. However, if heavy rainfall makes the lake water temporarily more desalinated, the number of tilapia increases, and fry literally swarm at the border of the source and the lake itself. In 1962, for example, thanks to the rains, tilapia filled the lake so much that even pink pelicans, lovers of our fish, tried to nest on it. However, I went again" black line“- either there was not enough oxygen in the water, or the amount of alkalis increased again, but one way or another, all the fish in the lake died. Do I need to explain that pelican nesting sites never appeared there?
Only one species of tilapia has adapted to life in hot springs - Tilapia grahami. However, there are SIX HUNDRED other varieties of these African fish. Some of them are quite interesting. Thus, Mozambican tilapia is bred in artificial ponds. However, the main “advantage” of tilapia for a zoologist is that it bears eggs IN THE MOUTH!