Why do fish have a “lateral line”?
nature has rewarded fish with a special organ for perceiving vibrations and movement of water - the lateral line.
It is known that the acoustic pressure in water is 2 times greater than the acoustic pressure in air. Water is practically incompressible; its density is 800 times greater than the density of air. All this creates favorable conditions for the propagation in the aquatic environment of vibrations, vortices, and jets caused by the movement of various bodies. The lateral line organs of fish are designed to capture both mechanical displacements of water particles and sounds (mainly low frequencies). Any creature moving near a fish causes at least a small movement of the water and thereby reveals itself. The sensitivity of the lateral line of fish is amazing: in experiments, fish detect the movement of a glass hair 0.25 mm thick at a distance of 20 to 50 cm.
What are the lateral line organs and how do they function? On both sides of the fish’s body, dotted lines are visually detected, running from the head to the tail of the fish. If you look closely, you will find that each dotted line represents a channel or groove filled with mucus. Sensitive cells of the lateral line are collected in kidney-shaped groups and hidden in canals that are washed by water.
The bodies of the sensitive cells contain a hair, which, when water acts on the mucus in the canal, bends and sends a signal to the auditory center of the fish. These hair cells are called neuromasts. Neuromasts of the lateral line organs densely cover the head and lateral surface of slow-swimming bottom-dwelling fish. A juvenile bream, for example, has almost 2000 such cells. They allow the fry to perceive a detailed picture of jet currents, learn about the direction of travel of waves on the surface of the water, navigate (without the help of vision) the bottom topography, the movements of prey or school neighbors, even become familiar with the shape of objects by fanning them from a distance of 3-4 cm with fins .
In fact, the lateral line serves as a distant sense of touch. For fish it is more necessary than vision. Avid fishermen rightfully claim that when fishing for pike, it doesn’t matter what the spoon looks like - it’s enough that it just sparkles in the water. Much more important is how it moves and vibrates during wiring. It has been established that the lateral line of both predators and peaceful fish perfectly captures infrasounds, which are formed as a result of the disruption of vortices from the surface of any streamlined bodies (fish, baits, boats, underwater hunters, etc.). Infrasonic noises are very “loud” during sudden changes in fish speeds (throws, turns, accelerations) and are most intense in fish with a poorly streamlined body shape.
In order to successfully hunt and escape from enemies, it is not enough for fish to see and hear well - by the way, their hearing is not that great - but here other senses come to their aid, and, above all, the so-called lateral line . This organ of the “sixth sense” is found only in fish and amphibians that constantly live in water. The lateral line is a canal that usually runs along the body from head to tail. The canal contains sensory papillae, connected to the external environment by tiny holes located in the scales, and by nerves to the brain. Sometimes the lateral line is discontinuous, and sometimes, as in herrings, it is located on the head.
The lateral line perceives even the slightest water vibrations and helps fish determine the strength and direction of the current, catch reflected water currents, feel movement in the school, and excitement on the surface. Using their “sixth sense”, fish can swim at night in muddy water without bumping into underwater objects or each other.
The lateral line also makes it possible to capture those vibrations that are transmitted to the water from the outside - as a result of soil shaking, impacts on the water, or a blast wave.
It was the lateral line that helped the fish feel the shaking of the table caused by the sounding alarm clock, as described in.
Fish feel such vibrations with much greater sensitivity than vibrations in the air. Therefore, experienced fishermen are careful not to knock on the boat, walk along the shore without stomping, but are not afraid to talk loudly.
The lateral line plays an extremely important role in predatory fish during hunting. For example, a blinded woman does not lose orientation in the water and accurately grasps a moving fish. But a blind pike with a destroyed lateral line loses its ability to navigate, it bumps into the walls of the pool and, even very hungry, does not pay any attention to the fish swimming nearby.
Among flounders there are often blind from birth, and they do not die, are normally well-fed and live to a ripe old age. This once again confirms that the lateral line plays a great role in the life of fish.
For peaceful fish, the “sixth sense” is also useful - it helps them detect enemies in time. Using the lateral line, peaceful fish distinguish the vibrations created by predatory fish from the vibrations created by their fellows. The fish perfectly “understand” that movement helps the predator to detect them, and therefore at night small fish stand calmly. Particularly typical in this regard is the behavior of the Atlantic herring, which sleeps “deadly” at night.
In addition to the “sixth sense”, touch and smell help fish navigate in the water. The organs of touch in some fish are located almost throughout the body, such as in. But most often they are located near the mouth. In cod, the organ of touch is the antennae on the lower lip. Our catfish has two long movable barbels, while its close overseas relatives have up to sixteen such barbels.
The deep-sea fish Gigantactis, which lives in the Indian Ocean, is armed with an amazing probe. The fish does not exceed five centimeters, but on its nose there is a probe almost the same length as itself. The probe ends in a luminous growth resembling a mushroom cap. Gigantactis deftly wields it, turning it up, down, right and left.
Some fish have organs of touch that look like a real beard. The deep sea devil fish looks funny. She has a whole spreading bush growing on her chin. This fish is the size of an orange. Found in the Atlantic Ocean at a depth of over 500 meters.
And the fish Ultimostomias Mirabilis, caught at a depth of 1800 meters, has a beard reaching 40 centimeters, while the fish itself is no longer than 4 centimeters.
In the Black Sea trigla and the deep-sea “walking” fish Benthosaurus, the elongated rays of the pectoral fins serve as organs of touch. In the labyrinth gourami fish, the pectoral fins are elongated into long thread-like processes. They are very mobile, and a gourami, without moving, can simultaneously feel objects with one whisker in front and the other in the back.
Many fish, including our freshwater ones, are guided by their sense of smell when searching for food.
In bony fish, the olfactory organs are paired nostrils. They are located on both sides of the head and lead into the nasal cavity. Water enters one hole and leaves another. This arrangement of the olfactory organs allows the fish to sense the odors of substances dissolved or suspended in water. However, during the current, the fish senses odors only in the stream carrying odorous substances, and in calm waters - only in the direction of the water currents. Anglers can tell you a lot about the sense of smell of fish. They know well that the smell of fresh bait made from rye crackers, hemp cake, and just cooked porridge attracts many peaceful fish.
Sharks can smell far away. When whaling ships are cutting up their prey, they gather around in masses.
As if by magic, South American piranha fish flock to the smell of fresh blood. Once you put a freshly killed animal into the river, it will soon be left with a cleanly gnawed skeleton.
When hunting, fish use several senses simultaneously.
Diurnal predators, when searching for prey, are guided mainly by vision and water vibrations.
The sense of smell in diurnal predators is poorly developed, but they still smell. often does not pay attention to a naked jig, but rushes towards it from afar if a worm or piece of fish is attached to the hook.
It is believed that some fish, such as the seahorse and beluga, use echolocation, that is, when they make sounds, they can catch their reflection from the bottom or other underwater objects. True, this has not yet been proven, but some fish have radars - devices that use electromagnetic waves rather than sound waves.
The muddy waters of the Nile are home to the long-snout fish, or water elephant. They named it so for its long snout, elongated in the form of a trunk. This is a large fish, reaching two meters in length. The Arabs have long treated the long-snout with superstitious fear, believing that it can see... with its tail. But in 1953, the East African Institute found that the water elephant has a kind of “alternating current generator” near its tail. The “batteries” of this “generator” have a voltage of about six volts. When discharged, the “batteries” create an electromagnetic field around the fish. If any object enters this field, it is distorted, and a special receiver on the fish’s back registers the distortion.
“Radar” allows the longsnout to detect a grain of sand falling behind its tail or a bait hanging on a hook. It is very sensitive, and it is no coincidence that the water elephant almost never gets caught in fishing nets.
Apparently, other fish that have electric organs also have a “radar system”: electric eels, electric catfish, and torpedo rays.
V. B. Sabunaev
"Entertaining ichthyology"
Sense organs play a very important role in the life and behavior of fish. Fish, like other vertebrates, have a full set of five senses. But they have a significant difference - the lateral line. In fish, this sense organ is called the sixth. Land animals lost it in the process of evolution, but waterfowl still have it and it makes their life quite significantly easier, helps them survive and feed.
Anatomy of a fish. Sense organs
The senses of smell and taste are considered to be one of the most important in fish. With their help, they are able to detect even minor changes in the environment. The pike fish, for example, not only feeds with the help of its mouth, but also, sensing a touch to the ground, instantly reacts, changing direction. Sensitive cells located in the mouth transmit nerve impulses, signaling danger, obstacles or food.
Fish have a rather finely developed sense of temperature. Such high sensitivity to fluctuations in temperature and pressure is unusual for terrestrial animals.
The olfactory organs of fish are located on the sides of the head and resemble small cones. With their help, they can detect changes in the chemical composition of water. The sense of smell is especially sharply developed in those animals that hunt at night. For example, a pike fish can smell prey that swims several meters away from it.
Side line. Location
Many scientists believe that the lateral line in fish is the most important sensory organ that helps animals live more comfortably. The lateral line is a kind of single center that unites all the sensitive cells in the body, located in the head or body.
The organ is located throughout the body, starting at the head and ending at the tail. The anatomy of fish, their variety and subspecies determine the location of the lateral line and its color. In one species it may appear as a bright white streak, in others it may appear as a dark, almost black stripe.
In a larger number of fish, the lateral line is represented in a single copy. But there are some species that can boast five or more. The lateral line of a fish can be very noticeable visually, or it can be hidden in the scales and immediately invisible to the human eye. In some fish it is arched, in others it is in the form of small abrupt stripes on the head.
There are fish that lack a sixth sense organ. These include mullet, dahlia, and some fish of the carp-tooth family.
The lateral line consists of...
As we have already said, the lateral line in a fish is a kind of brain and nerve center that allows you to control what is happening around you. What does this center consist of?
The lateral line is a cluster of a number of receptors that are located among themselves at a certain interval. Receptors can be located in channels on the head or in depressions that are located on the sides of the body. Most of the receptors are hidden under the skin of the fish. Only a few come to the surface and are hidden in the scales. Resembles open pores on the skin.
Inside, the lateral line canal is filled with fluid. Nerve receptors (their sensitive hairs), detecting changes, send a signal to this very liquid. Any movement, change in pressure or temperature of the water can cause the receptors and, consequently, the water in the canal to move. The stronger the changes in the fish’s habitat, the more the receptor hairs will deviate, the faster the information will enter the central nervous system.
The importance of the lateral line in fish
The sixth sense, or lateral line, allows fish to sense the approach of other animals living in the water much earlier than the organs of vision or smell tell them about it. The lateral line is capable of detecting minute changes in pressure in the water. Scientists say that the distance at which it is able to detect approaching danger is six times the size (length) of the fish itself.
The importance of the lateral line in fish with poor vision is especially great. There are animals that are able to react exclusively to shadow or light, while completely not noticing movement in the water. The lateral line in this case allows you to compensate for the underdevelopment or absence of visual or olfactory skills.
The life of a fish often depends on the lateral line. If it is damaged, then external influences will not be perceived so clearly by the animal. It will stop responding to danger from the outside, will not be able to fully hunt, get food, or hide from enemies. And soon he will die.
Lateral line and bite
Surely all experienced fishermen know the meaning of the lateral line of a fish. With its help, fish are able to detect the slightest noise and vibrations in the water. As experts say, a shot, an explosion, a normal conversation in a raised voice, a hit on the water will be immediately “seen” by the side line. And the fish, therefore, will react, get scared and hide. It is for this reason that fishermen try never to make noise on a pond, not to speak too loudly, and not to throw anything into the water.
Movement, slight noise and vibrations should be created not by the fisherman, but by the bait in the water. Experienced fishermen say that the bait should not stand in the reservoir, it must certainly move, making vibrations in the liquid. Only in this case will the fish smell food with its lateral line and move in the direction of the hook.
Surrounding water. Used for orientation and also for hunting. Externally it looks like a thin line on both sides of the body, stretching from the gill slits to the base of the tail. In some species, some of the lateral line receptors are transformed into electroreceptors and can detect electrical vibrations in the environment. Some representatives of crustaceans and cephalopods have similar organs.
Anatomy
The lateral line receptors are called neuromasts, each of which consists of a group of hair cells. The hairs are located in a convex jelly-like cupule, about 0.1-0.2 mm in size. Hair cells and neuromast cupules are usually found in the lower part of the grooves and pits that make up the lateral line organs. The hair cells of the lateral line are similar to the hair cells of the inner ear, suggesting that these organs have a common origin.
The lateral line organs of bony fishes and elasmobranchs have the form of canals, in which the neuromasts are connected to the external environment not directly, but through canal pores. Additional neuromasts may be present at various points on the surface of the fish's body.
Lateral line in fish
The development of the lateral line organs is associated with the animal’s lifestyle. For example, in actively swimming fish, neuromasts are usually found in canals rather than openings. The lateral line itself is located at the maximum distance from the pectoral fins, which may reduce the distortion that occurs when the fish moves.
Lateral line organs help fish avoid collisions, navigate water currents, and detect prey. For example, the blind cavefish Astyanax mexicanus has rows of neuromasts on its head that are used to accurately detect food in the absence of vision. Some carp-toothed fish are able to sense ripples that occur when an insect moves on the surface of the water. Experiments with pollock have shown that the lateral line is of key importance in the schooling movement of fish.
Links
- Lateral organs- article from
- Side line- article from the Great Soviet Encyclopedia
- // Encyclopedic Dictionary of Brockhaus and Efron: In 86 volumes (82 volumes and 4 additional ones). - St. Petersburg. , 1890-1907.
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