How and how fish are adapted to life in water?
Fish are the oldest vertebrate chordates that inhabit exclusively the aquatic habitat. both salty and fresh water bodies. Compared to air, water is a denser habitat.
In the external and internal structure, fish have adaptations for life in water:
The body shape is streamlined. The wedge-shaped head smoothly merges into the trunk, and the trunk into the tail.
The body is covered with scales. Each scale is immersed in the skin with its front end, and with its rear end it lies on the scale of the next row, like a tile. Thus, the scales are a protective cover that does not interfere with the movement of the fish. The outside of the scales is covered with mucus, which reduces friction during movement and protects against fungal and bacterial diseases.
Fish have fins. Paired fins (pectoral and pelvic) and unpaired fins (dorsal, anal, caudal) provide stability and movement in the water.
A special outgrowth of the esophagus helps fish to stay in the water column. Swimming bladder. It is filled with air. By changing the volume of the swim bladder, the fish change their specific gravity (buoyancy), i.e. Becomes lighter or heavier than water. As a result, they can be at different depths for a long time.
The respiratory organs in fish are the gills, which absorb oxygen from the water.
The senses are adapted to life in water. The eyes have a flat cornea and a ball-shaped lens. this allows the fish to see only closely spaced objects. The olfactory organs open outward with the nostrils. The sense of smell in fish is well developed, especially in predators. The organ of hearing consists only of the inner ear. Fish have a specific sense organ. the lateral line.
It has the appearance of tubules stretching along the entire body of the fish. Sensitive cells are located at the bottom of the tubules. The fish perceive all water movements with the side line. Due to this, they react to the movement of objects around them, to a variety of obstacles, to the speed and direction of currents.
Thus, due to the peculiarities of the external and internal structure, fish are perfectly adapted to life in the water.
What factors contribute to the onset of diabetes? Expand measures to prevent this disease.
Diseases do not develop on their own. Their appearance requires a combination of predisposing factors, the so-called risk factors. Knowledge of the factors involved in the development of diabetes helps to timely recognize the disease, and in some cases even prevent it.
Risk factors for diabetes mellitus are divided into two groups: absolute and relative.
The group of absolute risk of diabetes mellitus includes factors associated with heredity. This is a genetic predisposition to diabetes, but it does not give a 100% prognosis and a guaranteed undesirable outcome of events. For the development of the disease, a certain influence of circumstances, the environment, manifested in the factors of relative risk, is necessary.
Relative factors in the development of diabetes mellitus include obesity, metabolic disorders, and a number of concomitant diseases and conditions: atherosclerosis, ischemic heart disease, hypertension, chronic pancreatitis, stress, neuropathy, strokes, heart attacks, varicose veins, vascular damage, edema, tumors. endocrine diseases, long-term use of glucocorticosteroids, old age, pregnancy with a fetus weighing more than 4 kg and many, many other diseases.
Diabetes mellitus is a condition characterized by high blood sugar levels. The modern classification of diabetes mellitus, adopted by the World Health Organization (WHO), distinguishes several of its types: 1st, in which the production of insulin by b-cells of the pancreas is reduced; and type 2. the most common, in which the sensitivity of body tissues to insulin decreases, even with normal production.
Symptoms: thirst, frequent urination, weakness, complaints of itchy skin, weight change.
Oxygen, along with water temperature, is a factor that determines the metabolism of fish. For example, at a water temperature above 15 ° C, it is oxygen, and not temperature, that is the reason for limiting metabolism. Oxygen consumption depends on the type of fish, the structure of the gills, with the help of which the fish can effectively extract oxygen from the water. active fish need more oxygen, larger ones, as you know, too. The oxygen in water depends on various factors, in particular, the temperature of the water and the content of chlorine ions in it. In cold fresh water, saturation is higher than in warmer and richer chlorine ions. Scientists have found that the maximum concentration of oxygen in water bodies occurs in the middle of the day, and the minimum. at dawn.
The lack of oxygen in the water can be judged by the behavior of the fish. They accumulate near the surface, sometimes stick their noses out of the water and even jump out, trying to “get” oxygen from the air. On average, a favorable oxygen level is 7 mg / L and above. Fish living at low oxygen concentrations are more susceptible to diseases, and fry are lagging behind in development. If you find a dead fish with a wide open mouth and “protruding” gills of a pale shade, you should know that it died from asphyxiation.
When we say that we feel like a fish in water, we mean a state of complete comfort. Indeed, where else can fish thrive if not in their native element? But in reality, everything is much more complicated. It turns out that water, in order for fish to live really well in it, must not only be wet. It is necessary that it satisfies a variety of indicators.
How fish navigate the water
For thousands of years, different fish species have adapted to live in water with certain seasonal temperature limits. On the Chukotka Peninsula, in streams and shallow lakes, the dahlia fish is found, which freezes when water bodies freeze and comes to life when they thaw. Lucania fish lives and reproduces in the springs of mountainous California, where the water temperature is above 50 °. But these are isolated examples. Usually fish do not tolerate significant, and especially sharp fluctuations in temperature. After all, their body temperature is higher than the surrounding one by only a few tenths of a degree. The water temperature has a decisive influence on the distribution of fish and their vital functions. Each type of fish shows the greatest activity in a certain temperature range. For example, the optimum nutrition and reproduction for trout is observed at 10-12 °, for pike. at 15-16 °, for carp. at 23-28 °. Above and below a certain temperature, the fish stop eating altogether. In winter, in the northern regions and the middle lane, the life processes of many heat-loving fish freeze. Fish migrate to the depths, almost stop moving, stop feeding and, as it were, hibernate. Only some “frost-resistant” species. for example, like burbot, trout, salmon. remain active almost completely in winter.
Water is usually divided into fresh and salty. But this division is very arbitrary, since almost any natural water contains salt ions. With a salt concentration of up to 1 g / kg, water is considered fresh, up to 25 g / kg. brackish, and above it. salty. 1 kg of ocean water contains about 35 g of salt. Salt water contains more chlorides, fresh water contains more carbonates. Fish, of course, live in both water and wherever they like. However, some fish species can easily withstand significant fluctuations in salinity. For example, gobies feel great in water with m salts from tenths to 60%. Other fish are adapted only to a certain salinity. So, many perchiformes die when water is desalinated, and fish of the carp family cannot withstand salinization.
Hardness is determined by the presence of dissolved minerals in water and largely determines the rest of the properties of water. Traditionally, the most important “test” for minerals has been the soap’s ability to lather in a given water. This process usually involves Ca, Mg ions. Al, Fe, Mn, Sr, Zn, H. The hardness index is calculated in milligram equivalents per liter. Fresh water is very soft (up to 1.5 mEq / l), and the hardest water is sea water (about 130.5 mg / eq).
Water that is too soft cannot satisfy the needs of aquatic organisms, including fish, for calcium and magnesium. But these elements are necessary for fish no less than for humans. Other trace elements are also important. With a lack of iron in fish, anemia develops, with a lack of zinc, the skin and fins are affected, the absence of copper and manganese leads to bone deformation and abnormal development of the caudal fins. In general terms, we can say that the optimal water hardness for different types of fish may be different, but should not fall below 1.8 mg-eq / l.
If you were good at chemistry in school, then you probably remember about the pH value. Water molecules have the ability to partially decay into a positively charged hydrogen ion H and a negatively charged hydroxide ion OH-. The pH value just characterizes the concentration of H ions. If the pH is more than seven units, the water will have an alkaline reaction, if less, it will be acidic. Most fish are able to live in pH values in the 6.5-8 range. A sharp change in the acidity of the water leads to stress, illness or death of fish.
For example, if a fish is transplanted into water with a low pH value, which will differ from the initial one by several units, the fish will stop swimming and “freeze” in one position, and after a while will die. However, there are species that in natural conditions successfully adapt to acidic environment. So, for example, pike feels comfortable and reproduces in reservoirs with a pH of only 4 units.
The oxidizability index reflects the level of water pollution by organic substances. It is expressed in the amount of mg of oxygen required for the oxidation of organic matter in 1 liter of water. The source of organic suspensions in water is all living and dead aquatic organisms, excrement of fish and other aquatic inhabitants, decay products from soil and silt, sewage and animal husbandry. If the amount of organic matter is not too large, it is favorable for fish to live in the water. After all, all organic “waste” is ultimately processed by bacteria and form the basis of nutrition for many aquatic plants. If wastewater pollutes the reservoir above the limit, you need to sound the alarm.
The more organic matter is dissolved in the water, the more oxygen is required for their oxidation, and the harder it will be for fish to breathe. Fish quickly lose weight, their color becomes dark, conditions are created for the emergence of infectious diseases. Usually fish feel comfortable in water when 4-8 mg of oxygen per liter of water is consumed for oxidation of organic substances.
The concentration of ammonia, nitrites and nitrates (nitrogen pollution) also indicates the level of organic water pollution. In the course of their life, fish release ammonia into the water. The same substance can enter the reservoir with wastewater. Special bacteria living in the soil convert ammonia to nitrite and then to nitrate. Nitrates are practically harmless, but nitrites and ammonia itself are a terrible poison for fish. They attack their respiratory and immune systems. Nitrite enters the fish blood through the gills and causes hemoglobin oxidation. Brown gills and quick death. this is the result of poisoning with nitrogen compounds.
It helps fish to navigate in the water. How do fish navigate in the water? The most sensitive fish
Aromorphoses of fish
Fish differ from previous evolutionary forms with new, progressive features of the structure that have increased their level of organization. Let’s list them.
The appearance of the jaws and skull
In fish, the first pair of gill arches is modified in the jaw, with the help of which it becomes possible to feed. capture, crush prey. The skull appeared. the bone receptacle of the brain and sensory organs, which reliably protects these structures of the nervous system.
Precursors of the limbs, fins, paired appendages of the body, separated from the trunk and head, set in motion by muscular force are formed.
In cartilaginous fish, the notochord has a cartilaginous structure throughout life, and in bony fish, the notochord ossifies: the cartilaginous tissue turns into bone tissue. Chorda (axial skeleton) also called the spine.
This organ is characteristic exclusively for bony fish: it is absent in cartilaginous fish (sharks, rays). The swim bladder is an air bag filled with a mixture of gases: nitrogen, oxygen, carbon dioxide.
It performs a number of essential functions:
- Hydrostatic. helps fish to occupy a certain position in the water column. So, when the bubble expands, the fish floats, and when it decreases, it sinks to the bottom.
- Respiratory. able to perform lung function
- Baroreceptor. senses pressure changes
- Acoustic. perceives sounds, plays a role similar to the ear
When filled with gas, the bubble expands: this changes the specific gravity of the fish, it decreases and the fish floats. The reverse pattern occurs when the bubble decreases. But where does the gas come from that fills the bubble if the fish lives in water? Answering this question, we note that all fish are divided into two types: open-bubble and closed-bubble.
In open-bladder fish, the swim bladder communicates with the digestive system. Throughout their life, they rise to the surface of the water and swallow air, as needed, they can be freed from gases, squeezing them out through the pharynx and then through the mouth into the environment. These fish include herring, pike, carp, lungfish.
Closed-vesicular fish have a bladder that does not communicate with the digestive tube. Gases enter it due to gaseous secretion: they pass from a dissolved (in the blood) state to a gaseous state, filling the bubble. When the bubble decreases, the gases dissolve again in the blood, returning to the bloodstream. These fish include: cod-like, perch-like, mullet-like.
© Bellevich Yuri Sergeevich 2018-2020
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Bony fish are a thriving class, very numerous: they comprise about 95% of modern fish. This includes the most important subclasses that we will analyze: cartilaginous, lung-breathing and cross-finned fish.
The main orders of the class of bony fish are widely known:
- Sturgeon. sturgeon, sterlet, beluga
- Carps. crucian carp, carp, bream, silver carp
- Salmon. trout, salmon, salmon
- Codfish. cod, pollock, hake
- Perchiformes. perch, pike perch, mackerel, horse mackerel
Most bony fish are characterized by a bony skeleton, the presence of gill covers that cover the gills. The branchial lobes are located directly on the branchial arches, there is a swim bladder. Fertilization external.
We will consider this class using the example of a typical representative. river perch.
Integuments, musculoskeletal system
The shape of the body is streamlined, fish-like, due to which friction against water is reduced. The surface of the body is covered with overlapping scales (like tiles).
In most species, the scales are ctenoid (from the Greek Ktéis. comb and éidos. the type). equipped with teeth or thorns, or cycloid (from the Greek Kykloeides. circular, round). with a smooth rounded back edge.
The skin contains many glands that secrete mucus covering the entire body of the fish, thereby reducing friction against the water. Because of the mucus, the caught fish is hard to hold in your hands, it slips out.
Fins are the organs of movement of fish. Fins are both paired (pectoral, abdominal) and unpaired (dorsal, caudal, anal).
The skull is the seat of the brain, it surrounds it from all sides. The presence of the rostrum (from the Latin Rostrum. beak) is characteristic. the front elongated part of the fish skull.
The spine consists of two sections: trunk and caudal. There is a hole in the center of each vertebra. Adjacent to each other, the holes of the vertebrae are connected together to form a single spinal canal, in which the spinal cord lies.
The skeleton of the pectoral fins is connected to the spine by the bones of the shoulder girdle, in contrast to the skeleton of the pelvic fins, which is not articulated with the spine. There are gill covers that cover the gill slits from the outside (in cartilaginous fish, the gill covers were absent, 5 gill slits each opened outward separately.)
Secondary body cavity (whole).
The muscular system is segmented, which is expressed in the emergence of separate (differentiated) muscle bundles. The most striking example of differentiation is the muscles of the oral apparatus and paired fins.
Consists of the oral cavity, pharynx, continuing into the esophagus, stomach, large and small intestines. Many fish have a tongue in their mouths and sharp teeth located on their jaws. The teeth are not intended for mechanical crushing of food, but mainly for grasping and holding prey. Salivary glands are absent, there are taste buds.
In the lumen of the small intestine of fish, the ducts of the digestive glands, liver and pancreas, as well as the gallbladder open. There is no spiral valve in the intestine (typical for cartilaginous fish), the total absorption area increases due to blindly ending outgrowths of the intestine. pyloric appendages.
The pharynx is closely connected not only with the digestive system, but also with the respiratory system: the gill apparatus of fish is located here. With the help of gills, they have adapted to take oxygen dissolved in it from the water and saturate the blood with it, from where oxygen goes to the internal organs and tissues.
The breathing process is carried out due to the fact that water enters the pharynx through the mouth opening. Due to the movements of the operculum, water from the oropharyngeal cavity is drawn into the lateral branchial cavity, washing the gills. As a result of gas exchange, oxygen enters the blood of the fish, and carbon dioxide leaves it and dissolves in water.
The gills consist of a branchial arch, on which the gill rakers and petals are located. The branchial stamens are directed towards the oropharyngeal cavity and prevent the penetration of food particles into the gills (filter function). The branchial lobes are directed outward and braided by a dense network of blood vessels. capillaries, in which gas exchange takes place.
Like cartilaginous fish, bony fish have one circle of blood circulation. The heart is two-chambered, consists of one atrium and one ventricle. Remember that the heart of a fish is venous. It is pumped by the heart into the lungs, where it is saturated with oxygen, after which the blood becomes arterial.
Arterial blood is directed to internal organs and tissues, blood moves inside the vessels: the circulatory system is of a closed type.
Consists of paired ribbon-like trunk buds (mesonephros, or primary kidney.) They are located on the sides of the trunk. From the kidneys, the ureters begin, merging with each other and forming an expansion. the bladder.
Urine containing metabolic by-products is excreted from the fish’s body through the anus in females, through the urogenital opening in males.
All chordates have a tubular nervous system. The brain consists of the medulla oblongata, midbrain, cerebellum, diencephalon and forebrain.
The development of the same divisions in different classes of chordates is not the same, which we will clearly see as we study this section. I recommend that you pay special attention to this topic.
The nervous system is tubular. Compared to other classes of chordates, the brain in fish is poorly developed: the forebrain cortex is absent, instead the surface of the brain is covered with epithelium. The midbrain, the main coordinating center, reaches the greatest development.
The cerebellum is also well expressed (developed), which is responsible for the coordination of movements and the orientation of the body in space. This is due to the complex movements of the fish, which “hovers like a bird” only not in the air, but in the aquatic environment. 10 pairs of cranial nerves originate from the brain.
The sensory organs of the fish are represented by a special formation. a lateral line, stretching in the form of a channel along the entire body from both sides. Sensitive cells (neuromasts) of the lateral line organ react to changes in the direction and speed of water flow near the fish. With the help of it, the fish senses the direction and speed of water flow.
For the first time in fish, a specialized organ of hearing appears. the inner ear. With the help of it, they are able to distinguish sounds, orienting themselves in the aquatic environment. The inner ear consists of three semicircular tubules, an upper and lower sacs. Sometimes the inner ear is connected to the swim bladder (catfish, carp), due to which hearing in such fish is more developed.
The organs of vision are adapted to the aquatic environment: the lens has a spherical shape. Fish see well only at close range. There are taste organs on the skin and lower jaw, as well as olfactory organs that open into the oral cavity.
Fish are dioecious. The sex glands of males are the testes, of the females the only ovary. External fertilization occurs in the water: the female spawns (eggs), and the male releases sperm into the water, which merge with the eggs. Over time, young individuals develop from caviar.
Development in fish is direct, without metamorphosis. Remember that the process of spawning and then fertilizing eggs is called spawning and is seasonal. Freshwater fish spawn in spring, during which time fishing is strictly prohibited.
Fish are lower jaw-tootome primary-water vertebrates. About 33 thousand species of fish are known. An independent section of biology. ichthyology (from the Greek Ichthys. fish and logos. word) is devoted to them.
The first jaw-toothed fishes appeared in the Ordovician, cartilaginous fishes. at the boundary between the Silurian and Devonian, about 420 million years ago. Fish live in both fresh and salt waters. The fish superclass is divided into two subclasses: bony and cartilaginous fish.
The common features of all fish are the presence of a streamlined body, life in water. The body is subdivided into head, torso, and tail. The senses are well developed: sight, smell, hearing, touch, balance.
What helps fish navigate the water?
The fish do not have an outer and middle ear, but there is an inner one located in the region of the gill covers. The width of the spectrum of sound vibrations that are perceived by the inner ear depends not only on the environment, but also on the type of fish. Studies by ichthyologists show that most predators, on average, distinguish sound vibrations in the range from 20 to 1000 Hz. For example, chub, perch and asp. up to 2000 Hz, pike perch. from 20 to 600 Hz, pike. up to 1200 Hz, and catfish has a fairly sharp hearing. He hears sound vibrations up to 13,000 Hz due to the special structure of the inner ear.
But besides the inner ear, fish also have a lateral line, with the help of which the fish perceives sound waves of low frequency from 1 to 200 Hz. The organs of the lateral line of fish are designed to capture both mechanical displacements of water particles and sounds (mainly low frequencies). Any creature moving near the fish causes even a slight movement of the water and thereby reveals itself. The sensitivity of the lateral line of fish is amazing: in experiments, fish catch the movement of a glass hair 0.25 mm thick at a distance of 20 to 50 cm.
Vision is an important organ for fish, because it allows them to look out for prey, notice the enemy, hide from him, navigate in space, determine both the shape and size of objects, and the distance to them, and distinguish their color. Pisces can also distinguish colors, in about the same range as humans. In comparison with humans, however, they also perceive the short-wavelength region of the spectrum, which humans do not perceive as a color.
Fish detecting underwater objects is a passive location. Fish can be confidently called the first animals that have learned to own an active location. It is based on the fact that when moving in water, any object causes its wave-like vibrations.
Elephant fish or mormyrus.
Every minute the Mormyrus radar sends eighty to one hundred electrical impulses into space. The electromagnetic oscillations arising from the discharges of the “battery” are partially reflected from the surrounding objects and, in the form of a radio echo, again return to the mormir. “Receiver”. The echo catcher is located at the base of the dorsal fin of this amazing fish. Mormirus “probes” the surroundings using radio waves!
The report on the unusual properties of mormyrus was made in 1953 by the East African Ichthyological Institute.
The name “Mormyrus” was given by the ancient Greek scientist Aristotle.
Fish can taste even those parts of the body where there are no taste buds. with the help of ordinary skin. (By the way, there is an opinion among biologists that the so-called knocking of a perch or pike on a spoon, when a predator with a closed mouth hits the bait without grabbing it, is a specific “feeling” and “sniffing” of a strange prey by them.)
The famous American scientist, Nobel Prize laureate physicist R. Feynman once said: “There is practically not a single natural phenomenon that is not accompanied by electricity.”.
How does fish find food
The use of such techniques as baiting and baiting in fishing requires fishermen to know at least basic, elementary patterns of fish nutrition and methods of obtaining food by them, the role of the fish’s sense organs in the search for food. It is interesting to note that baiting and baiting are fundamentally different, albeit similar in sounding, fishing tricks. If bait means luring fish to any place convenient for the angler in the water area, then the bait is designed to tame fish to specific specific places where the fisherman regularly feeds.
So, the fish recognizes and searches for food, using for this purpose sight, smell, touch, lateral line and taste. Each species of fish has the most developed sense organs that are most often used when searching for and recognizing food.
The main sensory organ in fish is vision, but biologists say that absolutely all types of fish are myopic and see in the purest water at a distance of no more than 15 meters, and a clear image of objects is available to fish in the range of no more than 1.5-2 meters. However, studies have shown that each eye of a fish is able to simultaneously focus on different objects, that is, the fish has binocular vision, which significantly expands the view and makes it possible to control the situation almost everywhere around its axis.
Predators have much sharper vision than peaceful fish. In addition, the eyes of some fish species, such as pike perch, are adapted for vision at night. Fish are able to distinguish colors, but only at shallow depths of up to 10 meters, where the sun’s rays penetrate. Naturally, the maximum reaction in fish is manifested in the colors in which their favorite food components are painted, that is, various shades of yellow, red, brown and green (colors of larvae, worms, aquatic vegetation). It is for this reason that some baits are tinted with artificial or natural dyes, for example, beet decoction.
The nostrils are responsible for the smell of fish. From time immemorial, there has been a dispute between scientists and fishermen about the ability of fish to recognize smells, but in any case, everyone agrees that different flavors affect the behavior of fish in different ways. The indisputable truth is the use of various flavors in seasoning groundbait in minimal quantities: two or three drops of concentrated flavoring are enough for a kilogram of bait. Fishermen have not yet picked up universal smells, but the most often used are vanilla, anise, mint, laurel, cherry, cloves, cinnamon, garlic, dill and other components, as well as oils and tinctures developed on their basis.
The organs of touch in most fish species are practically not developed, but there are exceptions, such as catfish, carp, barbel, which nature has awarded with antennae on the lips. Ichthyologists cannot yet give an unambiguous answer about the role of whiskers in the life of these fish, but it is obvious that they are used by fish when searching for food.
The lateral line of the fish is responsible for the external perception of the world. With the help of specific sensitive cells on the body, the fish recognizes the smallest fluctuations in water and thus catches all objects moving around it and their sizes. That is why the angler needs to constantly take care of the activity of the bait. It has long been noted that wiggling worms on a hook attract fish much better than those that are not. The movements of the bait generate vibrations in the water, which the fish recognizes from long distances by means of the lateral line.
Finally, the taste. The generally accepted positions of fishermen on the presence of certain taste preferences of fish have also not been developed at the moment, but few will dispute the fact that fish distinguishes sweet from bitter, unleavened from salty and avoids sour in every way. Professional carp anglers have long enjoyed the carp fish’s fondness for sweetened boilies. Often honey, sugar and salt are used in the preparation of groundbait. Observations of fish show that some species repeatedly take food into their mouth and spit it out before eating food, recognizing the taste before swallowing.
It should be borne in mind that ichthyologists have a huge field of activity for further research on the sense organs of fish. But even now, the revealed patterns in the preferences of various types of fish, which have been transmitted to us by generations of scientists and fishermen, when used correctly in the preparation of baits and the selection of baits, as a rule, bring the desired result.