Development of conditioned reflexes in fish. Fish behavior and reflexes (Part 2). Conditioned reflex activity of fish

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Topic: “Formation of conditioned reflexes in aquarium fish”

All living beings are able to respond to changes in the external and internal environment, which helps them survive. The nature of the relationship between animals and their environment is determined by the level of development of the nervous system. The body's response to the influence of the external environment with the participation of the nervous system is called a reflex.

Acquaintance with the structural features of the nervous system in the seventh grade course begins with the study of fish. The nervous system of fish is represented by the brain and spinal cord. The anterior part of the fish brain is relatively small. The midbrain and its optic lobes are the most developed. Fish differentiate between the brightness of lighting, choosing places that are more suitable for a given species. Most fish also distinguish the color of an object. Fish distinguish red color especially well. The hearing organ of fish is represented only by the inner ear and consists of a labyrinth, including the vestibule and three semicircular canals located in three perpendicular planes. The diencephalon and cerebellum are well developed. This is due to the need for clear coordination of movements while swimming. The medulla oblongata passes into the spinal cord. Nerves that control the muscles of the body and fins extend from the spinal cord.

The development of the nervous system leads to a significant complication of all its departments. Outwardly, this manifests itself in the behavior of animals, which becomes more complex and multifaceted depending on the nature of the environmental influences on the body. The basis of all reactions of the body to irritation is a reflex. Acquired (conditioned) reflex - reactions with the help of which the body adapts to changing environmental conditions. Conditioned reflexes are formed throughout life. The formation of conditioned reflexes is the basis for teaching the body various skills and adaptations to a changing environment. Fish is the first animal studied in school in which the most primitive conditioned reflexes of a feeding nature can be formed. Various fish are suitable for these experiments, but the ability to learn varies from species to species.

A large amount of theoretical material has been accumulated on the behavior of fish. However, along with the fact that the number of works on the topic of conditioned reflex activity in fish is very large, there are practically no evolutionary systematic works on acquired forms of behavior within the class of fish, although they are used in similar studies for broader comparisons. That is why we were interested in the question of the development of conditioned reflexes in fish that are far from each other in systematic position.

The purpose of our work was to study and compare the rate of development of conditioned food reflexes to colored feeders (positive to red and negative to blue) in fish of different species, depending on their phylogenetic relationship.

In the process of achieving this goal, the following tasks were solved:

Study and analyze the literature on the peculiarities of the formation of conditioned reflexes in various types of aquarium fish;

Get acquainted with the structural features and physiology of the following types of aquarium fish: guppies, swordtails, speckled catfish;

To study and compare the rate of development of conditioned food reflexes to colored feeders (positive to red and negative to blue) in fish of different species, depending on their phylogenetic relationship;

To achieve the formation of conditioned reflexes in fish of different systematic categories.

This work was carried out in a classroom. In experiments on the study of conditioned reflex activity, fish of three species were used: one species from the suborder Catfish - the strong catfish, belonging to the family Calechtiidae, as well as two species of fish belonging to the family Poeciliidae - the swordtail (genus Xiphophorus) and guppies (genus Lebistes) .

The study with fish was carried out over two weeks. The experiment involved 10 fish: 3 guppies, 5 swordtails and 2 catfish. The fish were of different ages (fry and adults about one and a half years old), and the sex of the individuals was also taken into account. One aquarium with a volume of 20 liters was allocated for the experiment. Two feeders with different colors were also prepared: red and blue. The action of red light was reinforced by food, the action of blue light remained without reinforcement. Small bloodworms were used as food (unconditioned stimulus). The duration of the conditioned stimulus (the color of the feeder) was 10 seconds. Feed was supplied at the 6th second in the presence of a red feeder. During the experiment, the time the fish entered the feeding area, the time the food was eaten, the time the fish left the area, and other behavioral features of the test individual were recorded.

The experiments were carried out for two weeks, twice a day at different hours: 07.30 - morning feeding, 15.00. - evening feeding. Fish that came to the feeding zone after the red feeder was supplied, but before the food was supplied, that is, before the 6th second, were considered trained.

Consistent repetition of this result indicated the development of a positive conditioned reflex to the color of the red feeder. A negative conditioned reflex was considered developed if the fish, in the presence of a blue feeder, did not swim into the feeding area until the 10th second inclusive.

Subsequently, we compared the results obtained from experiments with different fish and drew conclusions about the ability to learn, that is, the development of conditioned reflexes for each fish species studied. We also took into account the age and sex characteristics of the fish.

Thus, we came to the conclusion that a clear development of a conditioned reflex (positive for red and negative for blue) is observed under these experimental conditions only in male swordtails of the sexually mature period of development. The females of this fish species made mistakes during the morning feeding hours, but always arrived at the feeding zone on time.

In representatives of fish of the guppy species, the reflex was developed later than in swordtails. The fish's reaction to the red color of the feeder occurred approximately after the 10th day of feeding. Here the females were more active and trainable. The fish began to purposefully move towards the feeder, but swam into the feeding zone mainly after the 10th second. The fry have not developed a conditioned reflex: a complete lack of reaction to the red and blue colors of the feeders. Perhaps this age group of fish requires a longer period of time to develop such a reflex.

We can talk about the absence of any reaction to the red and blue colors of the feeder in the speckled catfish. Obviously, to develop a reflex in this species, it is necessary to change the experimental design; perhaps catfish simply do not distinguish colors. It can also be assumed that this type of fish obtains food at the bottom and therefore does not strive for the surface of the water.

For a detailed analysis of the physiological mechanisms of fish behavior, there is often a need to study this behavior under experimental conditions, where precise dosage of factors that influence the fish and fine recording of body reactions are possible.

In an experiment, it is difficult to say that differences in fish learning are due to their phylogeny. Rather, the ecological characteristics of species have a greater influence on animal learning. But firmer statements can be made after deeper and longer research.

When studying fish, much attention is paid to the development of the concept of “reflex”; for the first time, a definition of the concept of “conditioned reflex” is given. It is important that students become convinced that fish develop a wide variety of reflexes and that they can be developed themselves.

The most accessible include experiments on the development of conditioned food reflexes to sound, light and other stimuli. Relatively quickly (in a week or two) you can train the fish to swim to a certain feeding place in response to signals such as tapping on the glass of the aquarium with a metal object (key, paper clip, coin), or turning on a flashlight light bulb.

During the lesson, when introducing the nervous system and behavior of fish, the teacher can ask students who have aquariums at home to say what conditioned reflexes the kept fish developed by themselves, and under what conditions they could have developed. Next, several students can be asked to develop a conditioned reflex to sound and tell how this work should be done.

Equipment and facilities. An aquarium with several fish of the same or different species; flashlight; light bulbs with reflectors; blue and red dyes.

Conducting the experiment. 1. Before conducting an experiment to develop a conditioned reflex to sound, fish must be left without food for several days. Then, before each feeding, you should knock on the wall of the aquarium with a coin or other metal object and, observing the behavior of the fish, give them a little food. The experiment is carried out daily. After the fish eat the food, they are given another small portion by tapping it on the wall of the aquarium.

The fish should be fed in the same place. The time between the action of the conditioned stimulus and its reinforcement with each feeding should be gradually increased. A conditioned reflex is considered developed when fish, after a signal, gather at the feeding site in the absence of food there.

Students should know that the developed reaction to a conditioned stimulus is preserved only if it is reinforced with food or another unconditioned stimulus.

2. In approximately the same way as in response to sound, a conditioned reflex to light is developed. The outside walls of the aquarium are reinforced with a light bulb from a flashlight. To prevent light from spreading in all directions, you can make a small reflector - a cone from a piece of foil glued to thick paper. The light bulb is connected to the battery by wires.

Before the experiment, the fish were not fed for 1-2 days. Students are asked to turn on the light, observe how the fish behave, and then give them some food. The experiment is repeated several times a day. At the same time, it is noted how the behavior of the fish changes, how many days later they will swim to the feeding place immediately after the light signal.

You can suggest the following experience. One small crucian carp is placed in two aquariums or jars with water and aquatic plants. After tapping on the wall of the aquarium, one fish is fed with food falling to the bottom (enchytraea worms, tubifex, bloodworms, small or cut earthworms), the other is fed with food floating on the surface (dry daphnia, gammarus, dry bloodworms). Each tap on the wall of the aquarium is accompanied by feeding.

During the experiment, it is determined after how many days (or, even better, after how many sessions of feeding and signal action) when crucian carp are placed in a common aquarium, one of them will go down while tapping, and the other will go up.

3. An interesting experiment is to determine the ability of fish to respond to colors. Two light bulbs with reflectors are mounted on the outer wall of the aquarium. One of the light bulbs is pre-painted red, the other blue. First, the fish develop a conditioned reflex to the red light. Then the blue and red lights are turned on alternately, and no food is given when the blue light is on. At first, the fish react to both lights, and then only to the red one. When the blue light turns on, braking is applied.

During the experiments, students can observe whether conditioned reflexes are developed equally quickly in different species of fish, for example, guppies or swordtails.

conclusions. 1. Fish form conditioned reflexes to various sounds, light, colors, and feeding places. 2. Conditioned reflexes are developed somewhat faster in predatory fish compared to peaceful ones. 3. Educated conditioned reflexes help them to better survive in a changed environment.

Reports on the results of experiments on the development of conditioned reflexes in fish are heard in a lesson on the study of the nervous system and behavior of fish if students were given preliminary tasks when completing the study of arthropods. If schoolchildren showed interest in carrying out the described experiments while familiarizing them with the nervous system and behavior of fish, then the results of work on developing conditioned reflexes in fish can be obtained for a lesson in which the nervous system and behavior of the frog as a representative of amphibians are considered.

Questions. How do conditioned reflexes differ from unconditioned reflexes? Why are conditioned reflexes formed under the condition of the simultaneous action of an unconditioned reflex? What is the importance of developing conditioned reflexes? What is the significance of the extinction of conditioned reflexes in the absence of their reinforcement by unconditioned stimuli?

STUDYING THE BEHAVIOR AND ADAPTATION OF FISH TO EXTERNAL CONDITIONS

The study of fish behavior is one of the most important tasks of ichthyology and an endless field for conducting the most interesting and fascinating experiments and research. In particular, preserving stocks of valuable anadromous and semi-anadromous fish in connection with hydraulic construction is impossible without successfully studying the behavior of these fish on spawning grounds, in the area of ​​dams and fish passage structures. It is equally important to prevent fish from being sucked into water intake structures. For these purposes, devices such as bubble curtains, electric fish barriers, mechanical screens, etc. are already used or have been tested, but so far the devices used are not sufficiently effective and economical.

For the successful development of the fishery and the improvement of fishing gear, information about the behavior of fish in the fishing zone, dependence on hydrometeorological conditions and hydrological factors, and daily and periodic vertical and horizontal migrations is extremely important. At the same time, rational organization of fishing is not possible without studying the distribution and behavior of groups of different ages. The timing and power of migrations, fish approaches to spawning, feeding, and wintering sites are largely determined by changes in environmental conditions and the physiological state of individuals.

The importance of the senses in the perception of abiotic and biotic signals

The study of fish behavior is carried out on the basis of regular field observations, experiments in laboratory conditions and analysis of data on the interaction of the higher nervous activity of the studied objects with the external environment. In the process of interaction with the environment, fish exhibit three methods of orientation:

Direction finding - reproduction of a signal coming from the outside world;

Location - sending signals and perceiving their reflections;

Signaling is the sending of a signal by some individuals and their perception by others.

The perception of abiotic and biotic signals that influence the behavior of fish occurs through the senses, among which are primarily vision, hearing, lateral line, and smell. The reflex activity of fish is of particular importance.

Fish vision

Compared to the air, water, as a habitat for fish, is less favorable for visual perception. The illumination of water layers by the sun's rays penetrating into the water is directly dependent on the amount of dissolved and suspended particles, which cause the turbidity of the water and determine the limits of action of the fish's visual organs. In sea water, illumination reaches a depth of 200-300 m, and in fresh water bodies only 3-10 m. The deeper the light penetrates into the water, the deeper the plants penetrate. Water clarity varies enormously. It is greater away from the coast and decreases in the inland seas. The more living organisms in the water, the less transparent the water. Very clear waters of the seas, especially a beautiful deep blue color, are waters poor in life. The most transparent seas are Sargasso and Mediterranean.

Pisces have color vision. For individuals living in the illuminated area, it is very important and determines their behavior. The feeding of planktivores, including juvenile fish, is carried out thanks to well-developed organs of vision. The visual acuity inherent in fish allows, depending on the illumination and transparency of the water, to distinguish objects at a distance of up to several tens of meters. All of the above is of great importance for the nutritional and defensive reactions of fish. It has been proven that the formation and disintegration of schools is also related to the illumination of the aquatic environment.

The movement of fish against the current is controlled by the organs of vision, and less often by the organs of smell. This is the basis for attempts to direct fish in fish ladders following the models. WITH Rhythms and feeding activity are related to illumination.

The phenomenon of vertical zonality and the predominant color of animals and plants is due to the uneven penetration of rays of different wavelengths into the water column. Animals are very often colored in the color of that part of the spectrum that penetrates to a given depth, as a result of which they acquire a protective coloring and seem invisible. In the upper horizons, animals are mostly colored brownish-greenish, and deeper - red. At great depths, devoid of light, animals are mostly colored black or completely devoid of color (depigmented).

Hearing.

The acoustic properties of water are much stronger than those of air. Sound vibrations travel faster and penetrate further. It has been established that the role of sound signaling increases with the onset of twilight, as visual perception decreases. The center of sound perception is the inner ear of fish. The perception of ultrasonic vibrations is not typical for fish, but they react to low-frequency sounds. The reaction to ultrasound is detected only when a powerful source is applied at a short distance and can most likely be attributed to a painful sensation in the skin.

When there is a reaction to sound signals, fish react directionally (reflexively), first of all, to food stimuli or a danger signal. Within the city limits, fish quickly get used to noise, even constant very loud sounds. This may be why it was not possible to organize the directed movement of salmon into rivers or scare them away from sewage using sound signals. Even near airfields, the fish do not change their behavior and continue to bite the bait. It has been noted that intermittent sound has a stronger effect on fish than constant sound.

Side line

First of all, it should be noted the functional connection of the lateral line with the hearing organs. It has been established that the lower part of sound vibrations (frequencies 1-25 Hz) is perceived by the lateral line. The significance of the lateral line has not been fully studied. The main function of the lateral line is the perception of hydrodynamic fields and jets of water. Hydrodynamic fields from large sources, causing a defensive reaction in fish, are usually perceived at a considerable distance. However, in areas where fast currents form in rivers below the dam, many fish quickly get used to the changed conditions.

Hydrodynamic fields caused by the movement of small bodies usually cause a feeding reaction in fish. With the help of the lateral line, fish are precisely oriented for an aimed throw over a relatively short distance of several tens of centimeters.

With the help of the lateral line, twilight, nocturnal and thicket predators orient themselves when reaching prey. For juvenile fish and planktivores, the lateral line serves to detect predators and general orientation in the environment.

Smell of fish

The property of water as a good solvent should be taken into account. It has been established that fish react to negligible amounts of substances dissolved in water. Fishermen use scents to attract fish. At the same time, other substances, such as tincture of the skin of predatory fish and marine mammals, act as a deterrent.

The perception of substances dissolved in water is apparently associated with the taste organs. Migratory fish find their way from the sea to rivers using their sense of smell. There is no doubt that fish are capable of remembering. This explains homing(from English home - ≪house≫) - the ability of fish to enter exactly those rivers, channels or rivers from which they emerged as fry after developing from eggs.

Higher nervous activity and behavior of fish

The ability of fish to acquire conditioned reflexes in combination with unconditioned reflexes makes it possible to control their behavior. Conditioned reflexes are developed in fish more slowly than in higher vertebrates, and quickly fade away if they are not reinforced by the same factors that contributed to their formation, but are capable of spontaneously arising after a certain time.

Water temperature plays a special role in the creation and extinction of reflexes. There is evidence (Yudkin, 1970) that sturgeons develop conditioned reflexes in the fall much worse than in the summer. In goldfish, a decrease in water temperature below +13 °C and an increase above +30 °C caused the disappearance of all previously acquired reflexes. All this becomes quite understandable if we consider that the vital activity of fish, animals with a low blood temperature, depends on the temperature of the water.

Conditioned reflexes can arise in fish in the form of imitation. Untrained fish imitate others whose conditioned reflexes have been formed after appropriate training or life experience. Very indicative in this regard is the change in fish behavior in the fishing zone of active and even stationary fishing gear. Often, one individual that has discovered a loophole to exit the fishing gear is enough for most of the flock to leave it (for example, anchovy in fixed and cast nets).

Pilengas is capable of overcoming net formations, waddling over the top fence, jumping out and even crawling, wriggling along an inclined surface when retrieving cast nets.

Observer pilots, who for a long time were engaged in guiding fishing vessels to schools of fish, noted a gradual change in the behavior of anchovy: a change in the direction of movement and exit from purse seines, “squatting,” dispersing, etc.

The behavior and speed of reactions of fish in different physiological states are not identical. Fatty fish quickly form aggregations that are more persistent than those formed by physiologically weakened individuals. Often fish react not only to sudden changes in conditions, but also to emerging trends in changes in environmental factors. With a slight increase in water temperature, accumulations may simply disintegrate, despite the fact that the temperature will remain within the optimal range for fishing.

The formation of fish in schools is of great importance. The defensive value of a flock of fish is as great as that of birds. Also, covering a larger area of ​​water, the school quickly finds feeding areas than individual individuals.

Observations have shown the presence of vertical migrations in some fish species. Thus, on the Newfoundland bank, at sunset, sea bass rises from depths of 500-600 m to depths of 300-400 m within 60-90 minutes. At night, the perch stays 200 m from the surface, and by morning it descends and is at the bottom during the day. Cod and haddock behave in a similar way. In the Black Sea, vertical migrations are most characteristic of anchovy and horse mackerel, descending to the lower horizons during the daytime and rising to the surface at night. This behavior is associated with the movement of plankton. For many fish, being at different depths and at different distances from the shore is typical at different periods of the life cycle.

All of the above is directly related to the behavior of fish. This must be taken into account by the researcher to more effectively influence the behavior of fish in fishing areas, where it is necessary to identify the leading factors for each specific case. Currently, knowledge of behavioral characteristics is of particular importance for the successful development of the fishery. And this is due, first of all, to an increase in fishing intensity, a fall in stocks and an increase in the economic cost of performing work.

The study of behavioral characteristics depending on environmental factors and the physiological state of fish allows researchers and fishermen to tactically regulate fishing and increase its efficiency. Knowledge of the biology of a commercial object allows fishing to be organized during periods of maximum concentrations, at depths of greatest distribution and at water temperatures when aggregations are most stable. One of the tools for such research is multifactorial correlative analysis of the most significant connections between oceanological and biological criteria for constructing mathematical models that describe the phenomena and processes of the life cycle of fish. For a long time and well in a number of basins, forecasts of the timing of autumn migrations, the formation and collapse of wintering aggregations and the beginning of the harvest of mass commercial fish have proven themselves. This helps reduce unproductive vessel downtime and increase fishing intensity.

As examples of such models, one can cite the regression equations calculated at AzNIIRKh to predict the timing of the autumn migration of the Azov anchovy through the Kerch Strait to the Black Sea.

Start of turn:

Y = 70.41 +0.127 X 1, -0.229 X 2,

Y = 27.68-0.18 X 2 - 0.009 (N).

Beginning of mass migration:

Y, = 36.01 +0.648 X 3 -0.159 X 2,

where U and U 1 are the dates of the expected beginning of autumn migration and mass movement (counting from September 1); X 1 and X3 - dates of the final transition of water temperature through +16 and +14 °C (respectively) in the southern part of the Sea of ​​​​Azov (counting from September 1); X 2 is the number of fish (in%) in the population with a body condition coefficient of 0.9 or more as of September 1, N is the duration of feeding (degrees/days) after spawning on September 1.

The error in forecasting the timing of the start of migrations according to the presented models does not exceed 2-3 days.

HIGH NERVOUS ACTIVITY OF LARVAL CHORDATES AND FISHES

The higher nervous activity of vertebrates reflects one of the important trends in their evolution - individual improvement. This trend is manifested in increasing life expectancy, a reduction in the number of offspring, an increase in body size, and increased conservatism of heredity. An expression of the same tendency is the fact that, on the basis of a limited number of species instincts, each individual, in the order of personal life experience, can form a larger number of diverse conditioned reflexes.

In such lower chordates as larval chordates and cyclostomes, conditioned reflexes are primitive in nature. With the development of analytical and synthetic activity of the brain and the use of increasingly subtle signals in fish, conditioned reflexes begin to play an increasingly significant role in their behavior.

Conditioned reflexes of larval chordates

Despite the regression of its nervous system, the ascidian can form a conditioned protective reflex of closing the siphons to a sound, or rather vibration-mechanical signal.

To develop such a reflex, a dropper was installed over the ascidian sitting in the aquarium. With each impact of a drop on the surface of the water, the ascidian quickly closed the siphons, and with more severe irritation (a drop falling from a great height) it pulled them inside. The source of conditioned signals was an electric bell mounted on a table next to the aquarium. Its isolated action lasted 5 s, at the end of which a drop fell. After 20–30 combinations, the bell itself could already cause protective movements of the siphons.

Removal of the central nerve node destroyed the developed reflex and made it impossible to form new ones. Persistent attempts to develop similar conditioned reflexes to light in healthy animals were unsuccessful. Obviously, the lack of reactions to light signals is explained by the living conditions of ascidians.

In these experiments it was also discovered that as a result of combinations of a signal with an unconditioned reaction, the latter was increasingly more easily evoked by the unconditioned stimulus. It is possible that such a conditioned increase in the excitability of the signaled reaction represents the initial summative form of temporary connection, from which more specialized ones then developed.

Cyclostomes

The sea lamprey reaches a meter in length. Every spring, sexual instinct forces her, like many sea fish, to leave the depths of the sea and rise into rivers to spawn. However, inhibition can be developed in response to this instinctive reaction (lamreys stopped entering rivers where they encountered polluted water).

Conditioned reflexes of the river lamprey were studied when reinforced by electric shocks. A light signal (2 lamps of 100 W), to which after 5–10 s of isolated action a 1–2 second unconditional electrocutaneous stimulation was added, already after 3–4 combinations it began to cause a motor defensive reaction. However, after 4–5 repetitions, the conditioned reflex decreased and soon disappeared. After 2–3 hours it could be produced again. It is noteworthy that simultaneously with the decrease in the conditioned defensive reflex, the magnitude of the unconditioned one also decreased. The threshold for electrodermal irritation to trigger a defensive reaction increased. It is possible that such changes depended on the traumatic nature of the electrical stimulation.

As was shown above using the example of ascidians, the formation of a conditioned reflex can manifest itself in an increase in the excitability of the signaled reaction. In this case, using the example of the lamprey, one can see how, when a conditioned reflex is inhibited, the exciter of the signaled reaction decreases. Having easily formed a conditioned defensive reflex to the light of a lamp, lampreys were unable to develop it to the sound of a bell. Despite 30–70 combinations of the bell with electric strikes, it never became a signal for defensive movements. This indicates predominantly visual orientation of lampreys in the environment.

The lamprey perceives light stimulation not only with the help of its eyes. Even after cutting the optic nerves or completely removing the eyes, the reaction to light remained. It disappeared only when, in addition to the eye, the parietal organ of the brain, which has light-sensitive cells, was also removed. Some nerve cells of the diencephalon and cells located in the skin near the anal fin also have photoreceptor function.

Having achieved high perfection in adapting to an aquatic lifestyle, fish have significantly expanded their receptor capabilities, in particular, due to the mechanoreceptors of the lateral line organs. Conditioned reflexes constitute an essential part of the behavior of cartilaginous and especially bony fish.

Cartilaginous fish. It is not without reason that the shark’s gluttony has become a proverb. Her powerful food instinct is difficult to slow down even with strong painful stimuli. Thus, whalers claim that a shark continues to tear and swallow pieces of meat from a dead whale, even if a spear is stuck into it. Based on such pronounced unconditioned food reactions, sharks in the natural environment apparently form many conditioned food reflexes. This is, in particular, evidenced by descriptions of how quickly sharks develop a reaction to accompany ships and even swim at a certain time to the board from which kitchen waste is thrown out.

Sharks actively use olfactory cues from food. They are known to follow wounded prey by following a trail of blood. The importance of smell for the formation of food reflexes was shown in experiments on small Mustelus laevis, free floating in the pond. These sharks found live hidden crabs in 10–15 minutes, and killed and opened ones in 2–5 minutes. If the sharks' nostrils were covered with cotton wool and Vaseline, they could not find the hidden crab.

Properties of the formation of conditioned defensive reflexes in Black Sea sharks (Squalus acanthias) studied using the technique described above for lampreys. It turned out that the sharks developed a conditioned reflex to the bell after 5–8 combinations, and to the lamp only after 8–12 combinations. The reflexes developed were very unstable. They were not stored for 24 hours, and the next day they had to be produced again, although this required fewer combinations than on the first day.

Similar properties of the formation of conditioned defensive reflexes were also discovered by other representatives of cartilaginous fish - stingrays. These properties reflect their living conditions. Thus, the spiny stingray, an inhabitant of the deep sea, needed 28–30 combinations to develop a reflex to a call, while the stingray, an active inhabitant of coastal waters, needed 4–5 combinations. These conditioned reflexes also revealed the fragility of temporary connections. The conditioned reflex developed the day before disappeared the next day. It had to be restored each time with two or three combinations.

Bony fish. Thanks to the enormous diversity in body structure and behavior, bony fish have achieved excellent adaptability to a wide variety of living conditions. The little one also belongs to these fish Mistichthus luzonensis(the smallest vertebrate, measuring 12–14 mm), and the giant “herring king” (Regalecus) southern seas, reaching 7 m in length.

The instincts of fish are extremely diverse and specialized, especially food and sexual instincts. Some fish, such as the vegetarian crucian carp, swim peacefully in muddy ponds, while others, such as the carnivorous pike, live by hunting. Although most fish leave fertilized eggs to fate, some of them take care of the offspring. Thus, blennies guard laid eggs until the young hatch. The nine-spined stickleback builds a real nest from blades of grass, gluing them together with its mucous secretions. Having completed the construction, the male drives the female into the nest and does not release her until she lays eggs. After this, he waters the eggs with seminal fluid and guards the entrance to the nest, from time to time ventilating it with special movements of the pectoral fins.

Freshwater fish from the family Cichlidae in case of danger, they hide the hatched juveniles in their mouths. They describe the special “calling” movements of adult fish, with which they collect their fry. The lumpfish leads the fry, which can be attached to the father's body with special suction cups.

A striking manifestation of the power of the sexual instinct of fish are seasonal migrations. For example, salmon migrate from the sea to rivers at certain times of the year to spawn. They are exterminated in droves by animals and birds, many fish die from exhaustion, but those remaining stubbornly continue on their way. In an uncontrollable rush to the upper reaches of the river, the noble salmon, encountering an obstacle, jumps onto the stones, breaks into blood and rushes forward again until it overcomes it. He jumps rapids and climbs waterfalls. The protective and food instincts are completely inhibited, everything is subordinated to the task of reproduction.

The relationships of fish in a school reveal a certain hierarchy of subordination to the leader, which can take various forms. Thus, they observe observations of a school of Malabar zebrafish, where the leader swims almost horizontally, which allows him to be the first to see and grab an insect that has fallen to the surface of the water. The remaining fish are distributed by rank and swim with an inclination from 20 to 45°. The pheromones they secrete play a major role in the behavior of fish. For example, when the skin of a gudgeon is damaged, toribons - chemical alarm signals - enter the water. It was enough to drop such water into an aquarium with minnows for them to run away.

Conditioned reflexes to sound stimuli. Aquarium lovers know well how you can train fish to gather at the surface of the water when signaled by tapping on the wall, if you practice this tapping before each feeding. Apparently, a similar conditioned food reflex determined the behavior of the famous fish of the monastery pond in Krems (Austria), which attracted the attention of tourists by the fact that they swam to the shore at the sound of a bell. Researchers who deny hearing in fish claim that fish swam only when they saw a person coming to the pond or when his steps caused the soil to shake. However, this does not exclude the participation of sound as one of the parts of a complex stimulus.

The issue of fish hearing has long remained controversial, especially since fish have neither a cochlea nor the main membrane of the organ of Corti. It was resolved positively only by the objective method of conditioned reflexes (Yu. Frolov, 1925).

The experiments were carried out on freshwater (crucian carp, ruffe) and sea (cod, haddock, goby) fish. In a small aquarium, the test fish swam on a string leash attached to an air transmission capsule. The same thread was used to supply electric current to the fish’s body; the second pole was a metal plate lying on the bottom. The sound source was a telephone handset. After 30–40 combinations of sounds with electric shocks, an auditory conditioned protective reflex was formed. When the phone was turned on, the fish dived without expecting an electric shock.

In this way, it was also possible to develop conditioned reflexes to various kinds of vibrations of water and other signals, such as light.

The defensive reflexes developed by reinforcement with electric current turned out to be very strong. They persisted for a long time and were difficult to extinguish. At the same time, it was not possible to develop reflexes to traces of signals. If the beginning of the unconditional reinforcement lagged behind the end of the conditioned signal by at least 1 s, the reflex was not formed. They also discovered that the development of one conditioned reflex facilitated the formation of subsequent ones. Based on the results of these experiments, one can judge a certain inertia and weakness of temporary connections, which, however, are capable of training.

It is not difficult to develop a conditioned food reflex to sound in the golden fish Orpha, accompanying the sound signal by lowering a bag of chopped worms into the aquarium. At the fish Umbra limi not only was a similar conditioned positive reflex formed to a tone of 288 oscillations/s, but also differentiation of a tone of 426 oscillations/s was developed, which was accompanied by the presentation of a lump of filter paper moistened with camphor alcohol instead of food.

To completely exclude the participation of vision, sound conditioned reflexes were developed on previously blinded dwarf catfish, minnows and loaches. Using this method, the upper limit of sound audibility was established, which turned out to be about 12,000 oscillations/s for the catfish, about 6,000 for the minnow, and about 2,500 for the loach. When determining the lower limit for the audibility of sounds, it turned out that fish perceive very slow (2–5 vibrations/s) and even single vibrations of water, which are not sounds to the human ear. These slow fluctuations can be made conditioned stimuli of the food reflex and their differentiation can be developed. Transection of the nerves of the lateral line organ destroys reflexes to low sounds, the lower limit of audibility rises to 25 Hz. Consequently, the lateral line organ is a unique organ of infrasound hearing in fish.

Recently, information has been accumulated about the sounds made by fish. It has long been known that Malay fishermen dive into the water to hear where a school of fish is. The “voices” of fish are recorded on a tape recorder. They turned out to be different in different species of fish, higher in fry and lower in adults. Among our Black Sea fish, the croaker turned out to be the most vocal. It is noteworthy that in the croaker a conditioned reflex to sound is formed after 3–5 combinations, i.e. faster than other fish studied, for example crucian carp, which required 9–15 combinations. However, the croaker develops conditioned reflexes worse in response to light signals (after 6–18 combinations).

Conditioned reflexes to light stimuli. Various conditioned reflexes based on food reinforcement were developed during training of fish in order to study their vision. Thus, in experiments with minnows, it was established that they differentiate light stimuli well by brightness, distinguishing between different shades of gray; it was also possible for fish to distinguish between hatched figures. Moreover, vertical hatching acquired a signal value faster than horizontal hatching. Experiments with perches, minnows and minnows have shown that fish can develop differentiation based on the shape of figures such as triangle and square, circle and oval. It also turned out that fish are characterized by visual contrasts that reflect inductive phenomena in the brain parts of the analyzers.

If you feed macropods with red chironomid larvae, the fish will soon attack the wall of the aquarium, when lumps of red wool, similar in size to the larvae, are glued to the glass outside. The micropods did not react to green and white lumps of the same size. If you feed the fish with pellets of white bread crumb, they begin to grab the white wool balls that come into view.

It is described that one day a coral predator was given a red-painted silverside along with a jellyfish tentacle. The predatory fish first grabbed the prey, but, having been burned by the stinging capsules, immediately released it. After that, she did not take red fish for 20 days.

Especially a lot of research has been carried out to study the properties of vision of carp. Thus, in experiments on the development of defensive conditioned reflexes to the presentation of lines as signals, it was shown that fish could differentiate them by the angle of inclination. Based on these and other experiments, suggestions have been made about a possible mechanism of visual analysis in fish using detector neurons. The high development of visual perception of carp is evidenced by its ability to distinguish the color of an object even in different lighting conditions. This property of constancy of perception was also manifested in carp in relation to the shape of an object, the reaction to which remained definite, despite its spatial transformations.

Conditioned olfactory, taste and temperature reflexes. Fish can develop olfactory and gustatory conditioned reflexes. After the minnow had been fed musky-smelling meat for some time, it began to respond with a typical search response to the previously indifferent musky odor. The olfactory signal could be the smell of skatole or coumarin. The signal odor was differentiated from those not reinforced by feeding. The smell of mucus covering their body can easily become a positive signal for minnows. It is possible that this natural reflex explains some of the gregarious behavior of these fish.

If earthworms fed to minnows are pre-soaked in a sugar solution, then after 12–14 days the fish will attack the cotton wool with the sugar solution placed in the aquarium. Other sweet substances, including saccharin and glycerin, caused the same reaction. You can develop conditioned taste reflexes for bitter, salty, and sour. The threshold for irritation by bitter turned out to be higher in the minnow, and lower by sweet than in humans. These reflexes did not depend on odor signals, since they persisted even after removal of the olfactory lobes of the brain.

Observations are described that show that the development of chemoreceptors in fish is associated with the search and detection of food. Carp can develop instrumental conditioned reflexes to regulate the salinity or acidity of water. In this case, the motor reaction led to the addition of solutions of a given concentration. In fish Poecilia reticulata Peters developed conditioned food reflexes to the taste of beta-phenylethanol with differentiation to coumarin.

Convincing evidence has been obtained that salmon, when approaching the mouth of the river where they were born, use their sense of smell to find their “native” spawning ground. The high selective sensitivity of their chemoreception is indicated by the results of an electrophysiological experiment in which impulses were recorded in the olfactory bulb only when water from the “native” spawning ground was passed through the nostrils of the fish, and were absent if the water was from a “foreign” one. It is known to use trout as a test object for assessing the purity of water after treatment facilities.

You can make the temperature of the water in which the fish swims a conditioned food signal. At the same time, it was possible to achieve differentiation of temperature stimuli with an accuracy of 0.4 °C. There is reason to believe that natural temperature signals play a large role in the sexual behavior of fish, in particular in spawning migrations.

Complex food-procuring reflexes. To better compare the indicators of conditioned reflex activity of different animal species, natural food-procuring movements are used. Such a movement for fish is to grab a bead suspended on a thread. The first random grasps are reinforced with food and combined with an auditory or visual signal, to which a conditioned reflex is formed. Such a conditioned visual reflex, for example, was formed and strengthened in crucian carp over 30–40 combinations. Color differentiation and a conditioned brake were also developed. However, repeated modifications of the signal meaning of positive and negative stimuli turned out to be an extremely difficult task for fish and even led to disorders of conditioned reflex activity.

Studies of fish behavior in mazes have shown their ability to develop a reaction to accurately choose the right path.

Yes, dark-loving fish Tundulus after 12–16 trials over two days, she began to swim through the openings of the screens, without going into dead ends, straight into the corner where food was waiting. In similar experiments with goldfish, the time required to find a way out of the maze over 36 trials decreased from 105 to 5 minutes. After a 2-week break from work, the acquired skill changed only slightly. However, the fish could not cope with more complex mazes, such as those used for rats, despite hundreds of trials.

Predatory fish can develop a conditioned reflex suppression of the hunting instinct.

If you place a crucian carp behind a glass partition in an aquarium with a pike, the pike will immediately rush at it. However, after hitting the glass with his head several times, the attacks stop. After a few days, the pike no longer tries to grab the crucian carp. The natural food reflex is completely extinguished. Then the partition is removed, and the crucian carp can swim next to the pike. A similar experiment was carried out with predatory perches and minnows. Predators and their usual prey lived peacefully together.

Another example of a conditioned reflex transformation of instinctive behavior was shown by an experiment with cichlid fish, whose eggs were replaced with eggs of a foreign species during their first spawning. When the fry hatched, the fish began to take care of them and protect them, and when at the next spawning they hatched fry of their own species, they drove them away as strangers. Thus, the developed conditioned reflexes turned out to be very conservative. Based on reinforcement with food and defensive reactions, fish developed various motor conditioned reflexes. For example, a goldfish was taught to swim through a ring and make “dead loops”; a brilliant betta fish, accustomed to pass through a hole in an obstacle, began to jump into it even when it was raised above the water.

The behavior of fish, their unconditioned and conditioned reflexes are largely determined by the environmental factors of the habitat, which leaves its mark on the development of the nervous system and the formation of its properties.

Development of defensive conditioned reflexes in fry. Regulation of river flows, construction of hydroelectric dams and reclamation systems to a greater or lesser extent complicate the path of fish to natural spawning grounds. Therefore, artificial fish farming is becoming increasingly important.

Every year, billions of fry, bred at fish hatcheries, are released into lakes, rivers and seas. But only a small part of them survive to fishing age. Raised in artificial conditions, they often turn out to be poorly adapted to life in the wild. In particular, fry that have no life experience in developing defensive reactions easily become prey to predatory fish, from which they do not even try to escape. In order to increase the survival rate of fry released by fish hatchery stations, experiments were undertaken to artificially develop in them protective conditioned reflexes to the approach of predatory fish.

In preliminary tests, the properties of the formation of such reflexes to visual, auditory and vibration signals were studied. If metallic shiny plates shaped like the body of a predatory bee-eater are placed among the roach fry, and a current is passed through these plates, then the fry begin to avoid these figures even in the absence of current. The reflex is developed very quickly (Fig. 84).

Rice. 84. Development of a conditioned defensive reflex in roach fry to look like a model of a predatory fish for 1 hour (according to G.V. Popov):

1 - 35-day-old fry, 2 - 55 days

To assess how much the development of artificial defensive reflexes can increase the survival rate of juveniles, we compared the rate at which the predator consumed fry that had undergone training and fry that had not had such training.

For this purpose, cages were installed in the pond. One predatory fish, a chub, and a precisely counted number of fish fry were placed in each cage. After 1 or 2 days, we counted how many fry remained alive and how many were eaten by the predator. It turned out that of the fry that did not develop defensive reflexes, almost half died within the first day. It is noteworthy that the second day adds practically little in this regard. One might think that the surviving fry manage to form natural conditioned defensive reflexes and successfully escape from the pursuit of a predator. Indeed, if they are taken into special experiments after such natural preparation, the percentage of death turns out to be either relatively small or even zero.

Fry with artificially developed conditioned defensive reflexes both to the sight of the figure of a predatory fish and to the shaking of the water, simulating its movements, suffered the least from the chub. In most experiments, the predator was unable to catch any of them even within two days.

A simple technique recently developed for instilling protective reflexes in commercial fish fry during their rearing can bring significant practical benefits to fish farming.