We all saw fish. They are very elegant in their coloring, and many people like to keep them as pets. Fish can be identified as the body of the animal body of a vertebrate animal or cannot be covered with scales and carries two sets of paired fins and many unpaired fins. fish are cold-blooded or ectothermic animals, which means that their body temperature continues to change with the temperature of the water. Fish are distributed in all aquatic habitats, ranging from mountain streams to the deepest oceans. About 32,500 species of fish are known, which together form the largest variety of organisms compared with other classes of vertebrates. Fish are also eaten by anglers and are kept in aquariums as a source of decoration. They are also associated with films, cultures and religions.
The term “fish” refers to an animal that offers any non-trap skull that carries gills throughout its life and has fins instead of limbs. Like other vertebrates, fish have different types and are classified by their nature. The main types of fish found in the modern world are moths, sharks, rays, lamprey, ray fish, melakanta and pulmonary fish. The fish has a streamlined body to quickly swim in the aquatic environment, has gills or respiratory auxiliary organs for oxygen and paired, as well as unpaired fins. Paired fins include the pectoral and pelvic fins. Unpaired fins - dorsal, anal and caudal fins. Usually, the body of the fish is covered with scales, but there are some fish that do not have scales and are smaller. Jaws very well developed in fish. They are ovoid.
Fish are usually cold-blooded vertebrates, but exceptions always exist. Tuna, swordfish and some shark species are adapted to warm-blooded categories. Optimization and efficiency of swimming fish also vary, for example, tuna, salmon and jacks can swim 10-20 body lengths per second, while eels and sharks can not move more than 0.5 body lengths per second. Some species of fish have the ability to extract oxygen directly from the air, as well as through other substances, because for this they have some specialized structures, for example, pulmonary fish have paired lungs, gouras have a maze and soma that release oxygen through the intestines or stomach. The shape of the body as well as the location of the fins are also different. Scales have different types, such as placoid, cosmoid, ganoid, cycloid, and crytoid. There are some fish that live on land, like mudskats, who live on silt and are concerned, hiding in their underground holes.
The size of the body of the fish varies from as small as a thick infant fish, whose length is only 8 mm, to the same height as that of white sharks 16 meters long. Many animals often mix with fish, as the term fish is associated with them like starfish, jellyfish, cuttlefish, clams. Strictly speaking, it is not a fish. Currently, there are 28,000 preserved fish, of which 27,000 are bony fish, 970 are sharks, rays and chimeras, and 108 are a hoe.
About 64 families of fish are monotypic, as they contain only one species. Currently, the total number of fish is about 32,500 people.
fish breathing through the gills present on both sides of the pharynx. The gills consist of a filiform structure known as filament. Each thread is supplied with a capillary network that increases the surface area for easy exchange of oxygen and carbon dioxide. the fish draws oxygen-rich water through the mouth and pumps it over the gills. In some fish, capillary blood flows in the opposition direction through the countercurrent system. The gills let in oxygen-poor water to the gill openings present on the sides of the pharynx. Sharks and lampreys have several gill openings, while some fish have one gill opening. The gill openings are covered with a protective coating called a feather cover.
The respiratory mechanism also changes in fish. Acne skin has the ability to absorb oxygen. The buccal cavity of electric eel can absorb oxygen. Some perch-like fish, cichlids are also able to breathe air directly, but the major of the fish depends on oxygen dissolved in water. Some air-breathing fish also hide them under wet burrows and show a temporary hibernation mechanism, and when plenty of water is available, they show airification, returning to the water. Fish can be opened or optional air ducts. African icefish fall into the category of mandatory air breathing when it comes to the surface of the water for air intake, otherwise it will die due to suffocation. Optional air ducts combine heavy fish, since most fish breathe oxygen dissolved in water, because they save energy by not rising to the surface of the water to swallow air. Catfish in the absence of dissolved oxygen can rely on oxygen dissolved in the gills.
The circulatory system of fish has the form of a closed loop. The heart pumps blood through this single loop to the whole body. The fish heart consists of four parts, including two chambers, one entrance and one outlet. The first part of the heart is sinus venosis, which is a thin-walled bag and collects blood from the vein of the body, before transferring it to the second part, which is the atrium. The atrium is a large muscular chamber that sends blood to the third part, which is the ventricle. The stomach is thick with a wall, and it transfers blood to the fourth part of the bulbous artery. From here, blood enters the aorta, and then into the gills for oxygenation.
The jaws of fish are very well developed and allow them to eat a wide variety of food materials, whether plant or animal. Swallowing food occurs through the mouth, and it breaks down into the esophagus. Digestion of food occurs in the stomach and in some fish, a characteristic finger, as a projection that represents the secret of digestive enzymes. These protrusions are called pyloric caeca. The pancreas and liver are also secret enzymes and help to easily digest food material. The whole process of digestion and absorption ends in the intestine. Fish waste is rich in ammonia, which means that they are ammoselichny. The waste leaves the body either through the gills or through the kidneys. Sea fish lose water through osmosis, and reverse occurs in the case of fresh fish. The kidneys secrete a diluted amount of urine. Scales in fish come from the skin.
The fish’s brain is comparatively small compared to other vertebrates, but some large fish, like sharks, have a mormida with larger brains than animals. The brain of fish consists of several parts. The anterior region is occupied by olfactory love, which receives and processes signals from the nostrils through two olfactory tracts. Olfactory love is usually very large in sharks, trenches and catfish, since they depend solely on the smell to catch their prey. Directly behind the olfactory shoulder straps is a two-blade structure called teleencephalon, which is equivalent to the brain of higher vertebrates. It is associated with the sense of smell. Both olfactory love and telencepahlon unite the forebrain of fish.
The forebrain is connected to the midbrain through the diencephalon. Diencephalon controls the function of regulating hormones and maintaining homeostasis. The pineal body is present just above the diencephalon, and it detects changes in light, circadian rhythms, and color changes. The midbrain or mesencephalon consists of two optical lobes that are large in those fish that prey on species, like rainbow trout and cichlids. The hindbrain or metencephalon performs the function of swimming and maintaining balance. The cerebellum is the largest structure of the brain, and it is monocotal. The whips and lamprey have small cereals, while the Mormirids have heavy cerebellums, as this is due to their electrical senses. The back of the brain is the brain stem or myelenecephalon. It manages muscle coordination functions along with breathing and osmoregulation.
Most fish have very well developed sense organs. All daily fish have well-developed color vision. Many fish are endowed with chemoreceptors that are responsible for unusual feelings of taste and smell. Although the fish have ears, they are not able to hear well. Sensory receptors form a system of side lines in fish, which detects the smallest currents and vibrations, as well as the movement of nearby prey. Sharks and catfish can also detect low level electrical currents. Electric coals create electrical currents. Experiments have shown that fish have good learning and memory skills.
An experiment conducted by William Tavolga at leisure, says that the fish have the ability to pain and fear. According to a study conducted by Scottish researchers from the University of Edinburgh and the Roslin Institute on rainbow trout in 2003, he shows that he shows behavior associated with pain, like other animals. Researchers injected bee venom and acetic acid into the lips of rainbow trout. The fish immediately began to rub lips on the walls of the tank, and this response was perceived as behavior aimed at alleviating pain in researchers. Neuron firing is similar to humans found in humans. Professor James D. Rose, however, argues that fish do not feel pain because they lack the neocortex.
Fish have a paired set of alternately located contact muscles on both sides of the spine. These compressive muscles form S-shaped curves that move down to the body and help in swimming. Fingers also increase the surface area of the tail for effective swimming. The streamlined body reduces frictional force. Many bony fish have a swim bladder that is filled with gas and helps maintain buoyancy. Although fish is ectothermic, exceptions always exist. Some fish are amphibious, as are sailors. Some fish maintain their body temperature in a higher range. All sharks of the Lamnidae family are endothermic. The degree of endothermy varies in different fish, although it is very expensive, but it provides such advantages as increased muscle strength, higher processing rates of the central nervous system and higher digestion rates.
The reproductive organs of fish include the testicles and ovaries. Most species of gonad have the same size and can be partially or completely fused. Secondary reproductive organs are also associated with reproductive organisms in order to increase its fitness. In terms of the distribution of spermatogonia, two types of testicles are found in the bones. In the first type, the testes are found in all the seminiferous tubules, while in other types of testes are present along with the distal part of the seminiferous tubules. The ovaries in fish are of three types. They can be high school students, secondary high school students and cistovaras. In the gymnasium ovary, the oocytes are released directly into the coelomic cavity, from where they enter the ostium and, finally, are removed through the oviduct. A secondary gymnastic ovary releases an egg cell into a stake, from where they fall directly into the oviduct. The Gnonnovarian ovaries are a primitive typification of the ovaries present in pulmonary fish, sturgeon and bowfin. Cystavariant kidneys are characteristics of most bones, since here the ovary is directly related to the oviduct.
The development of oogonia differs in different groups of fish and gives details of maturation, as well as the process of fertilization. Changes in the nucleus, ooplasm and surrounding layers determine the maturation of the oocyte. Postuulatory structures formed after the release of oocytes are absorbed by the process of apoptosis. Some fish are hermaphrodite, as they have testicles and ovaries in their bodies at different stages of their life cycle. About 97% of fish is ovoid. Common eggs are eels, tuna, goldfish, cichlids and salmon. In these fertilizations, fish occur outside the mother’s body, as parents lose their gametes in the surrounding water. Some egg-shaped fish also practice the method of internal fertilization, as the males use some nascent organ to deliver the spermatozoa to the female's sexual opening. Skates and horny sharks fall into this category. In these fish, the male uses clusters to deliver sperm cells to the body of the female.
Sea fish produce a large number of eggs in a column with open water, and the diameter of the eggs is about 1 mm. Newly hatched young fish from egg fish are called larvae. They are very delicate and carry a yolk sac for their nourishment and are very different in appearance compared to adults. The larval period is very short, and the larvae quickly lose the yolk sac and grow to the juvenile stage and begin to feed on zooplankton. Since zooplankton are present in insufficient quantities, many of them lose their lives because of hunger. Guppies, healers and angel sharks are ovoviviparous. Here the eggs develop inside the mother's body after internal fertilization and receive only the yolk as a means of nutrition.
Some species are viviparous. In some species, the mother saves eggs and feeds the embryos. Lemon sharks, splits and sickle-shaped perches are usually viviparous fish, where the embryo is fed through the placenta, similar to the structure found in mammals. In some viviparous sharks, developing embryos eat other eggs produced by the mother, and this phenomenon is called oofagia. Young gray nurses show intrauterine cannibalism, where a stronger young man devours weaker brothers and sisters. The immune system of fish is also variable. In the stray fish there are no real lymphoid organs. Red blood cells, macrophages and plasma cells are produced in the anterior part of the kidney and somewhere in the intestine, and they have a close resemblance to the bone marrow, as is the case with agave. In cartilaginous fish, the immune system is well developed and the epigonal organ surrounding the gonads, the Leydig organ in the intestinal walls and the intestinal volute are responsible for the production of immune cells. In cartilage fish, the spleen and thymus are well developed, which produce lymphocytes, macrophages and plasma cells. Bone fish demonstrates further advancement in the case of the immune system. In addition to the spleen and thymic gland, the scattered cells of the bony fish mucosa also act as immune tissues.
Like other animals, fish also suffer from an attack of parasites, as well as diseases. In order to remain free from disease, they have a well-developed defense system. The skin and scales, as well as the mucous secreted by the epidermis, prevent the penetration of microorganisms into the body of fish. The immune system also plays an important role in fighting infections. It is believed that the fish has evolved from a coral sea syringe.
According to the IUCN report in 2006, 1,173 species of fish are threatened with extinction. White sharks, Atlantic cod, devilish puppy are some of the endangered species. Overfishing is a very dangerous enemy of cod and tuna. Overfishing is responsible for the collapse of the fish population, since the production of offspring is under threat.
Water pollution, dam construction, water disposal for human use and the introduction of exotic species are also responsible for the destruction of the habitats of native species, and all this leads to a reduction in fish populations. The introduction of Nile perch into Lake Victoria has destroyed the lake cichlid population.
Also found fish associated with culture and religion. Collecting fish in the area for food and nesting only is called aggregation. Depending on the degree of their organization, fish schools or schools are formed. Weeds are free organizations where fish adjust their behavior and swimming movements in response to other members of the group. Schools of fish are close organizations representing all movements and other activities in one direction. Both schools and schools benefit fish in many ways.
We can conclude that nature has provided fish with a number of adaptive features that help them develop well in extreme conditions.
