Sense organs of fish, structure and their functions

Characteristic features of chordates:

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

During evolution, organs improved:

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

Biological meaning of all living things:

general characteristics

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

Life expectancy ranges from several months to 100 years.

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

Weight - from a few grams to 2 tons.

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

Hearing organs in fish

The fish has a pair of ears that are located behind the skull.
The function of the fish's ears is not only to detect sound vibrations, but also serve as the fish's balance organs. At the same time, the fish’s ear, unlike a person’s, does not come out. Sound vibrations are transmitted to the ear through fatty receptors, which pick up low-frequency waves generated by the movement of fish in the water, as well as extraneous sounds. Once in the fish's brain, sound vibrations are compared and, if strangers appear among them, they stand out, and the fish begins to react to them. Due to the fact that the fish has two lateral lines and two ears, it is able to determine the direction in relation to the sounds made. Having determined the direction of dangerous noise, she can hide in time.

Over time, the fish gets used to extraneous noises that do not threaten it, but if unfamiliar noises appear, it may move away from this place and fishing may not take place.

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Internal structure

Skeleton

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

swim bladder

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

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

Body cavity

Singing fish

It seems impossible to find a singing fish in nature. And they only speak in fairy tales. But scientists have identified some species that can communicate using sounds. True, this does not sound like the speech, growling or whistling of birds. Fish communicate using a special rhythm of releasing bubbles. Some are able to give certain signs through fins and gills. Naturally, fish “hear” not with their ears, but with their bodies.

More precisely, they feel vibration. The researchers took advantage of the ability of sound waves to travel quickly in an aquatic environment. Experiments carried out on common crucian carp showed that it is possible to train them to swim to the place of lunch when they hear a whistle. A month of training was enough for the whole school of fish to respond to sound.

Organ system

Digestive

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

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

Respiratory

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

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

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

Blood

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

excretory

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

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

Nervous

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

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

More about the sideline

Scientists consider this organ in fish to be one of the most ancient sensory formations. It can be considered universal, since it performs not one, but several functions at once, ensuring the normal functioning of fish.

The morphology of the lateral system is not the same in all fish species. There are options:

1. The very location of the lateral line on the body of the fish may refer to a specific feature of the species,
2. In addition, there are known species of fish with two or more lateral lines on both sides,
3. In bony fish, the lateral line usually runs along the body. For some it is continuous, for others it is intermittent and looks like a dotted line,
4. In some species, the lateral line canals are hidden inside the skin or run open along the surface.

In all other respects, the structure of this sensory organ in fish is identical and it functions in the same way in all types of fish.

This organ reacts not only to the compression of water, but also to other stimuli: electromagnetic, chemical. The main role in this is played by neuromasts, consisting of so-called hair cells. The very structure of the neuromasts is a capsule (mucous part), into which the actual hairs of the sensitive cells are immersed. Since the neuromasts themselves are closed, they are connected to the external environment through microholes in the scales. As we know, neuromasts can also be open. These are characteristic of those species of fish in which the lateral line canals extend onto the head.

In the course of numerous experiments conducted by ichthyologists in different countries, it was established for certain that the lateral line perceives low-frequency vibrations, not only sound waves, but waves from the movement of other fish.

How hearing organs warn fish of danger

In the wild, as well as in a home aquarium, fish take adequate measures when they hear the most distant sounds of danger. While the storm in this area of ​​​​the sea or ocean is still just beginning, the fish change their behavior ahead of time - some species sink to the bottom, where wave fluctuations are the smallest; others migrate to quiet locations.

Uncharacteristic fluctuations in water are regarded by the inhabitants of the seas as an approaching danger and they cannot help but react to it, since the instinct of self-preservation is characteristic of all life on our planet.

In rivers, the behavioral reactions of fish may be different. In particular, at the slightest disturbance in the water (from a boat, for example), the fish stop eating. This saves her from the risk of being hooked by a fisherman.

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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 fluid inside the membranous labyrinth contains auditory pebbles (otoliths), the vibrations of which are perceived by the auditory nerve. Fish have neither an external ear nor an eardrum. Sound waves are transmitted directly through tissue. The labyrinth of fish also serves as an organ of balance. The lateral line allows the fish to navigate, feel the flow of water or the approach of various objects in the dark. The lateral line organs are located in a canal immersed in the skin, which communicates with the external environment through holes in the scales. The canal contains nerve endings. The hearing organs of fish also perceive vibrations in the aquatic environment, but only higher frequency, harmonic or sound ones. They are structured more simply than other animals. Fish have neither an outer nor a middle ear: they do without them due to the higher permeability of water to sound. There is only the membranous labyrinth, or inner ear, enclosed in the bony wall of the skull. Fish hear, and they hear very well, so the fisherman must maintain complete silence while fishing. By the way, this became known only recently. Some 35-40 years ago they thought that fish were deaf. In terms of sensitivity, hearing and the lateral line come to the fore in winter. It should be noted here that external sound vibrations and noise penetrate through the ice and snow cover to a much lesser extent into the fish habitat. There is almost absolute silence in the water under the ice. And in such conditions, the fish relies more on its hearing. The organ of hearing and the lateral line help the fish to determine the places where bloodworms accumulate in the bottom soil by the vibrations of these larvae.

Sense organs

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

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

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

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

How do fish hear?

The fish's inner ear is connected to the swim bladder, which acts as a resonator that calms sound vibrations. Increased vibrations are transmitted to the inner ear, due to which the fish has good hearing. The human ear is capable of perceiving sound in the range from 20Hz to 20kHz, but the sound range of fish is narrowed and lies within the range of 5Hz-2kHz. We can say that fish hear worse than humans, about 10 times, and its main sound range is located within lower sound waves.

Therefore, fish in the water can hear the slightest rustle, especially walking on the shore or hitting the ground. Basically, these are carp and roach, therefore, when going for carp or roach, you should definitely take this factor into account.

Predatory fish have a slightly different structure of the hearing system: they have no connection between the inner ear and the air bladder. They rely more on their vision than on their hearing, since they cannot hear sound waves beyond 500 Hz.

Excess noise in a pond greatly affects the behavior of fish that have good hearing. Under such conditions, it may stop moving around the reservoir in search of food or interrupt spawning. At the same time, the fish is able to remember sounds and associate them with events. While conducting research, scientists found that noise has a very strong effect on carp and, in such conditions, it stopped feeding, while the pike continued to hunt, not paying attention to the noise.

Reproduction

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

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

Hearing organs in fish

Behind the skull of the fish there are a pair of ears, which, like the inner ear in humans, in addition to the function of hearing, are also responsible for balance. But unlike us, fish have an ear that does not have an outlet.

The lateral line picks up low frequency sound and water movement near the fish. Fatty sensors located under the lateral line clearly transmit the external vibration of water to the neurons, and then the information goes to the brain.

Having two lateral lines and two inner ears, the organ of hearing in fish perfectly determines the direction of sound. A slight delay in the readings of these organs is processed by the brain, and it determines from which side the vibration is coming.

Of course, on modern rivers, lakes and stakes there is enough noise. And over time, the fish’s hearing gets used to many noises. But regularly repeated sounds, even if it is the noise of a train, are one thing, and unfamiliar vibrations are another thing. So for normal fishing it will be necessary to maintain silence and understand how hearing works in fish.

The fish's senses include: vision, hearing, lateral line, electroreception, smell, taste and touch. Let's look at each one separately.

Organ of hearing and balance of fish

It is located in the back of the skull and is represented by a labyrinth; there are no ear openings, pinna and cochlea, i.e. the organ of hearing is represented by the inner ear. It reaches its greatest complexity in real fish: a large membranous labyrinth is placed in a cartilaginous or bone chamber under the cover of the ear bones. It has an upper part - an oval sac (ear, utriculus) and a lower part - a round sac (sacculus). Three semicircular canals extend from the upper part in mutually perpendicular directions, each of which is expanded into an ampulla at one end. The oval sac with the semicircular canals makes up the organ of balance (vestibular apparatus). The lateral expansion of the lower part of the round sac (lagena), which is the rudiment of the cochlea, does not receive further development in fish. An internal lymphatic (endolymphatic) canal departs from the round sac, which in sharks and rays comes out through a special hole in the skull, and in other fish it blindly ends at the scalp.

The epithelium lining the sections of the labyrinth has sensory cells with hairs extending into the internal cavity. Their bases are intertwined with branches of the auditory nerve. The cavity of the labyrinth is filled with endolymph, it contains “auditory” stones consisting of carbon dioxide (otoliths), three on each side of the head: in the oval and round sac and lagena. On otoliths, like on scales, concentric layers are formed, therefore otoliths, and especially the largest one, are often used to determine the age of fish, and sometimes for systematic determinations, since their sizes and contours are not the same in different species.

A sense of balance is associated with the labyrinth: when the fish moves, the pressure of the endolymph in the semicircular canals, as well as from the otolith, changes and the resulting irritation is picked up by the nerve endings. When the upper part of the labyrinth with semicircular canals is experimentally destroyed, the fish loses the ability to maintain balance and lies on its side, back or belly. Destruction of the lower part of the labyrinth does not lead to loss of balance.

The perception of sounds is associated with the lower part of the labyrinth: when the lower part of the labyrinth with the round sac and lagena is removed, the fish are not able to distinguish sound tones (when trying to develop a conditioned reflex). At the same time, fish without the oval sac and semicircular canals, i.e. without the upper part of the labyrinth, they are amenable to training. Thus, it was shown that the round sac and lagena are the sound receptors.

Fish perceive both mechanical and sound vibrations: with a frequency from 5 to 25 Hz - by the lateral line organs, from 16 to 13,000 Hz - by the labyrinth. Some species of fish detect vibrations located at the boundary of infrasonic waves by both the lateral line and the labyrinth.

Hearing acuity in fish is lower than in higher vertebrates, and is not the same in different species: ide perceives vibrations with a wavelength of 25–5524 Hz, silver crucian carp – 25–3840, eel – 36–650 Hz, and low sounds are picked up better by them .

Fish also pick up those sounds whose source is not in the water, but in the atmosphere, despite the fact that such sound is 99.9% reflected by the surface of the water and, therefore, only 0.1% of the resulting sound waves penetrate into the water. In the perception of sound in carp and catfish fish, a large role is played by the swim bladder, connected to the labyrinth and serving as a resonator.

It has long been known that fish react to sounds. Noise or sound can both frighten and attract fish; any noise created in the water irritates the fish. This is explained by the fact that fish can hear sounds arising in water at a considerable distance.

Fish can make sounds themselves. The sound-producing organs of fish are different: the swim bladder (croakers, wrasses, etc.), the rays of the pectoral fins in combination with the bones of the shoulder girdle (somas), jaw and pharyngeal teeth (perch and carp), etc. The strength and frequency of sounds produced by fish of the same type species, depends on gender, age, food activity, health, pain caused, etc.

The sound and perception of sounds is of great importance in the life of fish: it helps individuals of different sexes find each other, preserve the school, inform relatives about the presence of food, protect the territory, nest and offspring from enemies, and is a stimulator of maturation during mating games, i.e. serves as an important means of communication.

The reaction of different fish to extraneous sounds is different.

The main mechanoreceptors of fish are the auditory organs , which function as hearing and balance organs, as well as lateral line organs. The inner ear of elasmobranchs (sharks and rays) and bony fishes consists of three semicircular canals located in three mutually perpendicular planes, and three chambers, each of which contains otoliths. Some species of fish (for example, goldfish and various types of catfish) have a complex of bones called the Webber apparatus that connect the ear to the swim bladder. Thanks to this adaptation, external vibrations are amplified by the swim bladder, like a resonator.

The sensation of an electric field - electroreception - is inherent in many species of fish - not only those that can themselves generate electrical discharges.

Questions for self-control

1. What types of muscle tissue do you know?

2. List the main properties of muscle tissue?

3. What are the differences between striated and smooth muscle tissue?

4. What are the features of cardiac muscle tissue?

5. What types of nervous tissue do you know?

6. By what characteristics are nerve cells divided?

7. Describe the structure of a nerve cell.

Organs of touch in fish

The organs of touch in fish are fins, whiskers, rostrum, and fin rays. With the help of these organs, fish form a clear picture of the surrounding world. Naturally, baits, baits, groundbaits are also evaluated by these bodies. In particular, whiskers and fins touch objects and thus evaluation occurs. Pisces can either accept or reject objects if they make them wary.

Spilling fish have differently developed whiskers. In catfish, burbot and barbel, the whiskers move due to developed muscles. With the help of the fish's whiskers, the taste and density of the fish are determined by an object at the bottom. A mustache is very helpful in cases where it is dark and visibility is limited. If the mustache is damaged for any reason, then it quickly loses its functions.

Read: Useful properties of black caviar

The rays of the fins are of great importance in the fish’s perception of the surrounding world. They are located in almost all fins: on the back and belly. In some species the rays are long, in others they are short. With their help, fish explore the bottom in search of animal food.

Using rays on the fins of fish, the density of food and its composition are determined. This is a very important point for anglers to consider. This is why there is a difference in bait for roach, crucian carp and bream. Depending on what fish we are targeting and what time of year, one or another bait composition is selected. The density and composition of the bait largely determines whether we will be able to place the fish on the spot or not.

All fish develop tubercles on their heads during spawning. During the spawning period, these tubercles are the main sensory organs.

The organs of touch and tactile senses are more important for bottom fish - bream, catfish, burbot, eel, sleeper. It is these fish that have well-developed fins and whiskers. They help to navigate well in the bottom layer, find food and avoid predators.

Hearing in fish

Fish do not have ears. But this absolutely does not mean that the fish do not hear anything. Just the opposite. It’s just that the organ responsible for recording various sounds is located inside the body. This is a swim bladder. The principle of its operation is in many ways similar to how the human eardrum works. Vibrations of the walls of the bladder are signals that are transmitted through special channels to the brain. The swim bladder has a fairly large volume. Therefore, fish are able to hear sounds at different frequencies from great distances. That is why you should behave very carefully and not make loud sounds so as not to scare away the fish.

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But not only the swim bladder is the organ of hearing in fish. The lateral line and skin help to sense sound vibrations. The first organ perceives low sounds, and the second - loud sounds

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Hearing organs in fish

Behind the skull of the fish there are a pair of ears, which, like the inner ear in humans, in addition to the function of hearing, are also responsible for balance. But unlike us, fish have an ear that does not have an outlet.

The lateral line picks up low frequency sound and water movement near the fish. Fatty sensors located under the lateral line clearly transmit the external vibration of water to the neurons, and then the information goes to the brain.

Having two lateral lines and two inner ears, the organ of hearing in fish perfectly determines the direction of sound. A slight delay in the readings of these organs is processed by the brain, and it determines from which side the vibration is coming.

Of course, on modern rivers, lakes and stakes there is enough noise. And over time, the fish’s hearing gets used to many noises. But regularly repeated sounds, even if it is the noise of a train, are one thing, and unfamiliar vibrations are another thing. So for normal fishing it will be necessary to maintain silence and understand how hearing works in fish.

“Don’t make any noise to me here, otherwise you’ll scare away all the fish” - how many times have we heard a similar phrase. And many novice fishermen still naively believe that such words are spoken solely out of severity, a desire to remain silent, and superstition. They think something like this: a fish swims in water, what can it hear there? It turns out that there is a lot; there is no need to be mistaken about this. To clarify the situation, we want to tell you what kind of hearing fish have and why they can easily be scared away by some sharp or loud sounds.

Those who think that carp, bream, carp and other inhabitants of water areas are practically deaf are deeply mistaken. Fish have excellent hearing - both due to developed organs (the inner ear and lateral line), and due to the fact that water conducts sound vibrations well. So it’s really not worth making noise during feeder fishing. But how well does a fish hear? Just like us, better or worse? Let's look at this issue.

How well does a fish hear?

As an example, let’s take our beloved carp: it hears sounds in the range 5 Hz - 2 kHz .
These are low vibrations. For comparison: we humans, when we are not yet old, hear sounds in the range of 20 Hz - 20 kHz. Our threshold of perception begins at higher frequencies. So, in a sense, fish hear even better than us, but to a certain limit. For example, they perfectly capture rustles, impacts, and pops, so it is important not to make noise.

According to hearing, fish can be divided into 2 groups:

They hear very well - these are cautious carp, tench, roach

hear well - these are bolder perches and pikes

As you can see, there are no deaf people. So slamming a car door, turning on music, or talking loudly with neighbors near the fishing spot is strictly contraindicated. This and similar noise can nullify even a good bite.

Inner ear - movement of jelly and vibration of hairs

Pax 2,

Pax 2