MOSCOW STATE UNIVERSITY OF APPLIED BIOTECHNOLOGY.

DEPARTMENT OF ANATOMY, PHYSIOLOGY AND ANIMAL HUSBANDRY.

Coursework in Physiology and Ethology

farm animals.

« Conditioned reflex activity of fish

and its impact on productivity»

Written by: 2nd year student of group 9

Faculty of Veterinary and Sanitary Kochergin-Nikitsky K.

Lecturer: Rubekin E. A.

Moscow 2000-2001

PLAN.

I Introduction

II main part

A retrospective of the study of the reflex activity of fish.

Conditioned reflex activity of fish.

The influence of conditioned reflex activity on the productivity of fish

III Conclusion.

Among the many sections of the comparative physiology of vertebrates, a special place is occupied by the physiology of fish, which is rapidly developing both in our country and abroad. The growing interest of researchers in the physiological and biochemical foundations of fish life is determined by several reasons.

First, fish are the most numerous group of vertebrates in terms of species. The modern world ichthyofauna is represented by more than 20,000 species, the vast majority of which (95%) belong to bony fish. In terms of the total number of fish species, they significantly outnumber amphibians, reptiles, birds and mammals combined (about 18,000 species), and the process of describing fish species is still far from complete, since descriptions of new dozens of fish species appear every year and painstaking work continues to clarify species independence. many "subspecies" with the involvement of modern methods of biochemical systematics.

Secondly, fish are taxonomically very heterogeneous groups of aquatic vertebrates. Fish is the same collective concept as "terrestrial vertebrates", consisting of several classes. The macroheterogeneity of fish is recognized today by most ichthyologists-systematists, and the only question is how many classes are included in the superclass of fish? According to L. S. Berg, there are 4 classes: cartilaginous, chimeras, lungfish and higher fish, and, according to T. S. Russ and G. L. Lindberg, there are only 2 classes: cartilaginous and bony fish. It should, perhaps, be noted that the division of fish into classes, even in our time, is carried out exclusively according to morphological characters, without taking into account modern data of evolutionary physiology, biochemistry and molecular biology.

Thirdly, fish are the most ancient group of vertebrates, the phylogenetic history of which is at least 3 times longer than that of birds and mammals. In addition, within each of the two main classes of fish (cartilaginous and bony), there are evolutionarily older and younger orders, or the so-called progressive and primitive. All this is of great interest to specialists in the field of evolutionary physiology and biochemistry and makes fish an obligatory object of evolutionary physiological research in the understanding of L. A. Orbeli (1958), i.e., in the development of problems of the evolution of functions and functional evolution.

Fourth, fish are an extremely ecologically diverse group of vertebrates. As a result of a long adaptive evolution, they have mastered almost all ecological niches in the oceans, seas, lakes and rivers, adapted to living in mountain lakes and the deepest oceanic depressions, in drying up reservoirs and underground caves, in arctic waters and hot springs. In other words, fish are an indispensable object of ecological and physiological research, the focus of which is on the physiological and biochemical mechanisms of adaptation to ever-fluctuating environmental factors.

Fifth, and this is especially important, fish are of great economic importance as a source of food protein for humans and farm animals. Recall that today, of the total amount of protein consumed by mankind, terrestrial ecosystems provide about 98%, water - 2%, that is, almost 50 times less. At the same time, however, it should be borne in mind that the share of animal protein of “terrestrial” origin is only 5% (the remaining 93% are vegetable protein), and animal protein of “aquatic” origin is 1.9%, i.e. 30% of the animal protein consumed by mankind. As the world's population increases, the need for animal protein will constantly increase and in the future it will not be possible to satisfy them at the expense of "land animal husbandry". The growing shortage of food protein makes us face the need to further increase the volume of fish catch in the World Ocean, which, however, has already reached 90 million tons per year, i.e., has come close to the level of the maximum possible catch (about 100-120 million tons per year), the excess of which will inevitably lead to catastrophic consequences. Therefore, the main increase in fish production in the World Ocean and inland waters can only be obtained through the development of maritime and aquaculture on an unprecedented scale, as well as the artificial reproduction of the most valuable fish species by obtaining viable juveniles in fish hatcheries with their subsequent release to feeding pastures in natural areas. reservoirs. In addition to meeting the need for protein, a person also uses fish products such as fish oil (obtained from cod liver) as a source of vitamin D in medicine and animal husbandry. In medicine, drugs derived from sharks are used. In animal husbandry - fishmeal. Everyone knows such products as salmon and sturgeon caviar.

Humanity has been engaged in fish farming, in particular the pond cultivation of carp, for more than 2000 years, but more empirically than on a scientific basis. This is due to the fact that a person receives the bulk of seafood through hunting, and not breeding. In the current century, the intensive development of fish farming has shown that the solution of these large-scale fishery problems is possible only on the basis of a comprehensive study of the main objects of fish farming and fishing, on a deep understanding of the general patterns and mechanisms of interaction of fish with the main factors of the aquatic environment that determine the normal course of life in natural and artificial conditions. , without the knowledge of which neither the rational establishment of fish farming nor the management of managed fisheries in natural reservoirs are inconceivable.

Retrospective of the study of the reflex activity of fish

So, fish is the most numerous, extremely diverse in terms of phylogenetic age, living conditions, lifestyle and level of development of the nervous system, a group of vertebrates perfectly adapted to the environment, which is also of great economic importance as a source of food protein.

The foundations of domestic fish physiology were laid in the 20-40s of the current century by the studies of X. S. Koshtoyants, E. M. Kreps, Yu. P. Frolov, P. A. Korzhuev, S. N. Skadovsky, A. F. Karpevich, G. S. Karzinkin, G. N. Kalashnikov, N. L. Gerbilsky, V. S. Ivlev, E. A. Veselov, V. A. Pegelya, T. M. Turpaeva, N. V. Puchkov and many others. It was during these years that the first data were obtained on the physiology of blood, digestion, respiration, osmoregulation, reproduction and behavior, as well as on the metabolism of fish and the influence of individual factors of the aquatic environment on it. These were the first steps towards the physiological "identification" of fish, the identification of their characteristics in comparison with other classes of vertebrates, as well as the differences between groups of fish of different phylogenetic age.

Acquired forms of behavior are usually opposed to innate responses, although a sharp line between such forms of behavior may not always be drawn, since an innate response in its original, primitive form can be developed even in the embryonic period (Hind, 1975). Complex complexes of long-term motivated behavior, usually referred to as instincts, contain elements in which the role of innate reactions is undoubted, but also acquired forms of behavior are also undoubted. It is customary to call the instinct of self-preservation, which is inherent in almost the entire period of life, although to varying degrees. This instinct is expressed in various forms of defensive behavior, primarily passive-defensive. Anadromous fish are characterized by a migratory instinct - a system of behavioral acts that promotes passive and active migrations. All fish are characterized by a food-procuring instinct, although it can be expressed in very different forms of behavior. The possessive instinct, expressed in the protection of territory and shelters, upholding the sole right to a sexual partner, is far from known for all species, sexual - for all, but its expression is very different.

Complexes of simple behavioral acts that have a certain sequence and purposefulness are sometimes called dynamic stereotypes - for example, a certain series of actions when obtaining a discrete portion of food, going to a shelter, building a nest, caring for protected eggs. The dynamic stereotype also combines innate and acquired forms of behavior.

Acquired forms of behavior are the result of an organism's adaptation to changing environmental conditions. They allow you to acquire cost-effective, time-saving standard reactions. In addition, they are labile, that is, they can be redone or lost as unnecessary.

Different pisciformes have different complexity and development of the nervous system, so the mechanisms for the formation of acquired forms of behavior are different for them. For example, acquired reactions in lampreys, although they are formed with 3-10 combinations of conditioned and unconditioned stimuli, are not developed during the time interval between them. That is, they are based on persistent sensitization of receptor and nerve formations, and not on the formation of connections between the centers of conditioned and unconditioned stimuli.

The training of laminabranchs and teleosts is based on true conditioned reflexes. The rate of development of simple conditioned reflexes in fish is approximately the same as in other vertebrates - from 3 to 30 combinations. But not every reflex can be developed. Food and defensive motor reflexes are the most well studied. Defensive reflexes in the laboratory are studied, as a rule, in shuttle chambers - rectangular aquariums with an incomplete partition that allows one to move from one half of the chamber to the other. As a conditioned stimulus, an electric light bulb or a sound source of a certain frequency is most often used. As an unconditioned stimulus, an electric current from a network or a battery with a voltage of 1-30 volts, supplied through flat electrodes, is usually used. The current is turned off as soon as the fish moves to another compartment, and if the fish does not leave, then after a certain time - for example, after 30 seconds. The number of combinations is determined when the fish performs the task in 50 and 100% of cases with a sufficiently large number of experiments. Food reflexes are usually developed for any action of the fish by rewarding the issuance of a portion of food. The conditioned stimulus is a light being turned on, a sound being emitted, an image appearing, etc. In this case, the fish should come to the feeder, press the lever, pull the bead, etc.

It is easier to develop an "environmentally adequate" reflex than to force the fish to do something that is not characteristic of it. For example, it is easier to make an eared perch, in response to a conditioned stimulus, grab a tube from which feed paste is squeezed out of its mouth than to throw a float from below. It is easy to develop in the loach the reaction of leaving to another compartment, but it is not possible to make it move while the conditioned and even unconditioned stimulus is acting - such a movement is not characteristic of this species, which is characterized by hiding after a jerk. Persistent attempts to force the loach to constantly move along the annular channel lead to the fact that it stops moving and only flinches from electric shocks.

It should be said that the "abilities" of the fish are very different. What works with some instances doesn't work with others. A. Zhuikov, studying the development of defensive reflexes in juvenile salmon grown at a hatchery, divided the fish into four groups. In some fish it was not possible at all to develop a motor defensive reflex in 150 experiments, in another part the reflex was developed very quickly, the third and fourth groups of experimental fish acquired the skill of accurately avoiding electric shock during an intermediate number of lamp ignitions. Studies have shown that fish that learn easily are significantly better at avoiding predators, while those that learn poorly are doomed. After salmon chicks are released from the hatchery, after a period of time sufficient to undergo rigorous selection while living with predators (fish and birds), the learning ability of the survivors is much higher than that of the original material, since the "incapable" become food for predators.

The simplest form of learning is getting used to an indifferent stimulus. If at the first demonstration of a frightening stimulus, for example, a blow to the water, the wall of an aquarium, a defensive reaction arises, then with repeated repetition, the reaction to it gradually weakens and, finally, completely stops. Fish get used to a variety of stimuli. They get used to living in conditions of industrial noise, periodic drawdown of the water level, eye contact with a predator, fenced off by glass. In the same way, the developed conditioned reflex can be inhibited. With repeated presentation of a conditioned stimulus without reinforcement by an unconditioned stimulus, the conditioned reflex disappears, but after some time the "deception" is forgotten, and the reflex may spontaneously arise again.

During the development of conditioned reflexes in fish, the phenomena of summation and differentiation may occur. An example of summation is provided by numerous experiments, when a reflex developed to one sound frequency or to one color of a light source manifested itself upon presentation of other sound frequencies or colors. Differentiation occurs in the presence of the resolving power of the receptor organs in fish: if food reinforcement is given at one frequency and pain at another, then differentiation occurs. In fish, it is possible to develop second-order reflexes, that is, reinforcement is given after the light source is turned on only if it is preceded by a sound stimulus. The reaction in this case is observed directly to the sound without waiting for the light. In the development of chain reflexes, fish are inferior to higher animals. For example, in children, reflexes up to the sixth order can be observed.

HIGH NERVOUS ACTIVITY OF LARVAR-CHORD CYCLOSTOMES AND FISH

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

In such lower chordates as larval-chordates and cyclostomes, conditioned reflexes are of a primitive nature. With the development of the analytical-synthetic activity of the brain and the use of more and more 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 ascidia can form a conditioned protective reflex of closing the siphons to a sound, or rather, a 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 ascidia quickly closed the siphons, and with stronger irritation (drop falling from a great height), it pulled them in. The source of the 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 evoke defensive movements of the siphons.

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

In these experiments it was also found that as a result of combinations of a signal with an unconditioned reaction, the latter was more and more easily evoked by the unconditioned stimulus. It is possible that such a conditional increase in the excitability of the signaled reaction is the initial summation form of a temporary connection, from which more specialized ones developed later.

cyclostomes

The sea lamprey reaches a meter in length. The sexual instinct every spring makes her, like many marine fish, leave the depths of the sea and rise into the rivers for spawning. However, inhibition can be developed for this instinctive reaction (lampreys stopped entering rivers where they encountered polluted water).

The conditioned reflexes of the river lamprey were studied during reinforcement with electric shocks. A light signal (2 lamps of 100 W), to which, after 5–10 s of isolated action, a 1–2 second unconditioned electrocutaneous stimulation was added, after 3–4 combinations, it itself 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 developed again. It is noteworthy that, simultaneously with a decrease in the conditioned defensive reflex, the value of the unconditioned one also decreased. The threshold of electrocutaneous stimulation to evoke a defensive reaction was increased in this case. It is possible that such changes depended on the traumatic nature of the electrical stimulation.

As was shown above with 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 lamprey as an example, it can be seen how, when the conditioned reflex is inhibited, the causative agent of the signaled reaction decreases. Easily forming 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 shocks, it never became a signal for defensive movements. This indicates a predominantly visual orientation of lampreys in the environment.

Lamprey perceives light stimuli not only with the help of the eyes. Even after transection of the optic nerves or complete removal of the eyes, the reaction to light persisted. 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 a photoreceptor function.

Having achieved high perfection in adaptation 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. The shark's gluttony is proverbial for a reason. Its powerful food instinct is difficult to slow down even with strong pain stimuli. Thus, whalers claim that the shark continues to tear and swallow pieces of the meat of a dead whale, even if you stick a spear into it. On the basis of such pronounced unconditioned food reactions in sharks in a natural setting, many conditioned food reflexes are apparently formed. This, in particular, is evidenced by descriptions of how quickly sharks develop a reaction to escort ships and even swim at a certain time to the board from which kitchen waste is thrown.

Sharks use olfactory food signals very actively. They have been known to follow wounded prey on a trail of blood. The importance of smell for the formation of food reflexes was shown in experiments on small Mustelus laevis, floating freely in the pond. These sharks found live hidden crabs in 10–15 min, and dead and opened crabs in 2–5 min. If the sharks had their nostrils covered with Vaseline cotton, they could not find the hidden crab.

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

Similar properties of the formation of conditioned defensive reflexes were also found by other representatives of cartilaginous fish - rays. These properties reflect the conditions of their life. Thus, the spiny stingray, an inhabitant of the sea depths, needed 28–30 combinations to develop a reflex to a call, while 4–5 combinations were enough for a mobile inhabitant of coastal waters, the stingray. In these conditioned reflexes, the fragility of temporary connections also manifested itself. 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. Due to the enormous diversity in body structure and behavior, bony fish have achieved excellent adaptability to a wide variety of habitat conditions. The little one belongs to these fishes. Mistichthus luzonensis(the smallest vertebrate, 12-14 mm in size), and a giant "herring king" (Regalecus) the southern seas, reaching 7 m in length.

The instincts of fish, especially food and sex, are extremely diverse and specialized. 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 their fate, some of them show concern for offspring. For example, blennies guard the laid eggs until the juveniles hatch. The nine-spined stickleback builds a real nest of blades of grass, sticking them together with its mucous secretions. Having completed the construction, the male drives the female into the nest and does not release it until she spawns. After that, he waters the eggs with seminal fluid and guards at 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. Pinagora leads fry, which can be attached to the father's body with special suckers.

Seasonal migrations are a striking manifestation of the strength of the sexual instinct of fish. For example, salmon at certain times of the year rush from the sea to rivers to spawn. Animals and birds exterminate them in masses, many fish die from exhaustion, but the rest stubbornly continue on their way. In an irresistible rush to the upper reaches of the river, the noble salmon, meeting an obstacle, jumps on stones, breaks into blood and again rushes forward until it overcomes it. He jumps rapids and climbs waterfalls. Protective and food instincts are completely inhibited, everything is subordinated to the task of reproduction.

The relationship of fish in a flock reveals a certain hierarchy of subordination to the leader, which can take various forms. Thus, observations are made of a flock 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 rest of the fish are distributed according to ranks and swim with an inclination of 20 to 45 °. A large role in the behavior of fish is played by the pheromones they secrete. For example, when the minnow's skin is damaged, toribons, chemical alarm signals, enter the water. It was enough to drop such water into an aquarium with minnows so that they rushed to flight.

Conditioned reflexes to sound stimuli. Aquarium hobbyists know well how to train fish to gather at the surface of the water at the signal of tapping on the wall, if you practice this tapping before each feeding. Apparently, such a conditioned food reflex determined the behavior of the famous fish of the monastery pond in Krems (Austria), attracting 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 the fish swam only when they saw a person coming to the pond or when his steps caused the ground to shake. However, this does not exclude the participation of sound as one of the parts of the complex stimulus.

The question of the hearing of fish has long been controversial, especially since the fish has 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, ruff) and marine (cod, haddock, goby) fish. In a small aquarium, the test fish swam on a leash tied to an air transfer capsule. The same thread was used to bring electric current to the body of the fish, the second pole was a metal plate lying on the bottom. The source of the sound was a telephone receiver. 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 possible to develop conditioned reflexes also to various kinds of water vibrations and other signals, such as light.

The defensive reflexes developed on 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 for traces of signals. If the beginning of the unconditioned reinforcement lagged behind the end of the action of the conditioned signal by at least 1 s, the reflex did not form. It was also found 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 a golden orphan fish, 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 to a tone of 288 oscillations/s formed, but also a differentiation of the tone of 426 oscillations/s was developed, which was accompanied by the supply of a lump of filter paper moistened with camphor alcohol instead of food.

In order to completely exclude the participation of vision, sound conditioned reflexes were developed on previously blinded pygmy catfish, minnows and loaches. In this way, the upper limit of the audibility of sounds was established, which turned out to be about 12,000 vibrations / s for the catfish, about 6000 for the minnow, and about 2500 for the char. When determining the lower limit of the audibility of sounds, it turned out that fish perceive very slow (2–5 vibrations / s) and even single vibrations of water, which for the human ear are not sounds. These slow fluctuations can be made conditioned stimuli of the food reflex and their differentiation can be worked out. 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 kind of infrasonic hearing organ 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 learn by ear where a school of fish is. The "voices" of the fish are recorded on a tape recorder. They turned out to be different in different fish species, higher in fry and lower in adults. Among our Black Sea fish, the croaker turned out to be the most "vociferous". It is noteworthy that in the croaker, the conditioned reflex to the sound is formed after 3–5 combinations, i.e. faster than other studied fish, such as crucian carp, which required 9–15 combinations. However, the croaker develops conditioned reflexes to light signals worse (after 6–18 combinations).

Conditioned reflexes to light stimuli. A variety of conditioned reflexes to 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 in terms of brightness, distinguishing between different shades of gray, it was also possible to distinguish between hatched figures by fish, and vertical hatching acquired a signal value faster than horizontal. Experiments with perches, minnows and minnows have shown that fish can differentiate according to the shape of such figures as a triangle and a square, a circle and an oval. It also turned out that visual contrasts are characteristic of fish, reflecting induction phenomena in the brain parts of the analyzers.

If you feed macropods with red chironomid larvae, then soon the fish attacked the aquarium wall when lumps of red wool, similar in size to the larvae, were glued to the glass outside. The micropods did not respond to green and white lumps of the same size. If you feed the fish with spools of white bread crumb, then they begin to grab the white woolen lumps that are in sight.

They describe that once a coral predator was given a red-painted satin along with a jellyfish tentacle. The predatory fish at first grabbed the prey, but, having burned themselves on 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 on the study of the properties of vision of carps. 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 were made about a possible mechanism of visual analysis in fish using detector neurons. The high development of the carp's visual perception is evidenced by its ability to distinguish the color of an object even in different lighting conditions. This property of perceptual constancy manifested itself in the carp in relation to the shape of the object, the reaction to which remained definite, despite its spatial transformations.

Conditioned olfactory, gustatory and temperature reflexes. Fish can develop olfactory and gustatory conditioned reflexes. After being fed musk-scented meat for some time, the minnow began to respond with a typical exploratory reaction to a previously indifferent musky smell. The smell of skatole or coumarin could be used as an olfactory signal. The signal odor was differentiated from those not reinforced by feeding. Very easily becomes a positive signal for minnows the smell of mucus covering their body. It is possible that such a natural reflex explains some of the properties 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 pounce on cotton wool with a sugar solution lowered into the aquarium. Other sweet substances, including saccharin and glycerin, evoked the same reaction. You can develop taste conditioned reflexes to bitter, salty, sour. The threshold of irritation for minnow turned out to be higher for bitter, and lower for sweet than in humans. These reflexes did not depend on olfactory signals, since they persisted even after the 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 for and discovery of food. Carps can develop instrumental conditioned reflexes to regulate salinity or acidity of water. In this case, the motor reaction led to the addition of solutions of a given concentration. At the 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, 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 the “alien” 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 conditional food signal. At the same time, it was possible to achieve differentiation of temperature stimuli with an accuracy of 0.4 °C. There are reasons to believe that natural temperature signals play an important role in the sexual behavior of fish, in particular, in spawning migrations.

Complex food-procuring reflexes. For a better comparison of indicators of conditioned reflex activity of different animal species, natural food-procuring movements are used. Such a movement for fish is the grasping of a bead suspended on a string. 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 in 30–40 combinations. Differentiation by color and a conditional brake were also developed. However, repeated modifications of the signal value of positive and negative stimuli proved to be an extremely difficult task for fish and even led to disturbances in conditioned reflex activity.

Studies of the behavior of fish in labyrinths have shown their ability to develop a reaction of unmistakably choosing the right path.

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

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

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

Another example of a conditioned reflex transformation of instinctive behavior was shown by an experiment with cichlid fish, which, during their first spawning, had their eggs replaced with caviar of an alien species. When the fry hatched, the fish began to take care of them and protect them, and when they brought fry of their own species to the next spawning, they drove them as strangers. Thus, the developed conditioned reflexes turned out to be very conservative. On the basis of reinforcement with food and defensive reactions, various motor conditioned reflexes were developed in fish. For example, a goldfish was taught to swim through a ring, to make “dead loops”, a brilliant betta fighting fish, accustomed to pass through a hole in a barrier, 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. The regulation of the flow of rivers, the construction of hydroelectric dams and reclamation systems, to a greater or lesser extent, makes it difficult for fish to reach natural spawning grounds. Therefore, artificial fish farming is becoming increasingly important.

Every year, billions of fry hatched at hatcheries are released into lakes, rivers and seas. But only a small part of them survive to commercial age. Grown in artificial conditions, they often turn out to be poorly adapted to life in the wild. In particular, fry that have not had life experience in the formation of protective reactions easily become the prey of predatory fish, from which they do not even try to escape. In order to increase the survival rate of fry released by fish breeding 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 vibrational signals were studied. If, among the roach fry, shiny metal plates shaped like the body of a bee-eater are placed, and a current is passed through these plates, then the fry begin to avoid these figures even in the absence of a current. The reflex is developed very quickly (Fig. 84).

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

1 - 35 day 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 a predator eats fry that have undergone training and fry that have not had such training.

For this, cages were installed in the pond. One predatory fish was placed in each cage - a chub and a precisely counted number of fish fry. 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 perished during the first day. It is noteworthy that the second day adds little in this regard. It can be assumed that the surviving fry have time to form natural conditioned defensive reflexes and successfully escape from the persecution of the predator. Indeed, if they are taken after such a natural preparation in special experiments, then the percentage of death turns out to be either relatively small, or even zero.

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

The recently developed simple technique for educating protective reflexes in the fry of commercial fish during their rearing can bring significant practical benefits to fish breeding.