Fish is the oldest vertebrate. They inhabit almost all aquatic environments on earth-from fresh lakes and rivers to salty seas and oceans.

There are about 24,000 species of fish in the world. Two-thirds of people live in seawater, and the rest live in fresh water. There are 2,500 species in China, among which more than 100 species can be used for medicine. Common medicinal animals are seahorse, sea dragon, Monopterus albus, carp, crucian carp, sturgeon (swim bladder glue), large yellow croaker (otolith is brain stone), shark and so on. In addition, it is often used as raw material for pharmaceutical industry. For example, the liver of cod, shark or ray is the main raw material for extracting cod liver oil (vitamin A and vitamin D). Hydrolyzed protein, cytochrome C, lecithin and cephalin can be extracted from various fish. The liver and ovary of fugu contain a lot of tetrodotoxin, which can be extracted to treat neuropathy, spasm, tumor and other diseases. The bile of large fish can be extracted as "bile pigment calcium salt", which is the raw material for artificial production of bezoar.

Fish live in seawater or fresh water all their lives, and most of them have bodies and fins suitable for swimming. Breathe through gills and prey on the upper and lower jaws. There is a beating heart divided into an atrium and a ventricle. The blood circulation is single circulation. The appearance of spine and head makes fishes develop into a kind of vertebrate that can best adapt to life in water. This is because water is different in depth, and the pressure is different in different places. The sea level is 1 atmospheric pressure, while the deep sea area can reach 1000 atmospheric pressure. The range of salt content in fresh water and seawater is 0. 001~ 7% from fresh water to salt water. In addition, with the different geographical environment, the temperature difference and oxygen content of water are also very different. Due to the diversity of these waters, water layers, water quality, biological factors and abiotic factors in water, the posture structure of fish has changed differently to adapt to different external changes. Higher than the rotifer class.

Fish is the largest class in the existing subphylum of vertebrates. From the point of view of animal evolution, this class is the beginning of jaw, so it is the most primitive and oldest class among jaw. This is the largest taxonomic group in the subphylum of vertebrates. As far back as Devonian, many marginal branches have been derived, which have developed and evolved into various complex fish. The existing fishes are divided into cartilaginous fishes and bony fishes.

1. Chondrichthyes

This strain is the lowest group of existing fish, with about 200 species in the world and more than 40 species/kloc-0 in China, most of which live in the sea.

Its main features are:

① There is no hard bone for life, and the endoskeleton is composed of cartilage.

② Most of the body surfaces are covered with scales.

③ The branchial interval is well developed and there is no gill cover.

④ Skew caudal fin. This line is divided into two subclasses, namely Claudiobranchia and Holocephala.

2. Skeletal fishes (Osteichthyes)

Skeletal fish is the largest group of fish in the world, with more than 20 thousand species, most of which live in sea water and some in fresh water.

Its main features are:

(1) The bones are hardened into hard bones in different degrees.

② The body surface is covered with hard scales, round scales or comb scales, and a few species are degraded without scales. Mucous glands of the skin are well developed.

(3) The branchial septum is partially or completely degenerated, and the gills are not directly open to the outside, but covered by bony branchial cover. The water flowing out of branchial fissure is discharged through the rear edge of branchial cover, and most of them have swim bladder.

(4) Fish tails are often straight, with original or crooked tails.

⑤ Most of them are fertilized in vitro and oviparous, and a few of them are abnormal during development.

The earliest fish was a fish with a round mouth and no jaws that appeared on the earth during the Cambrian period 450 million years ago. Fish can be easily distinguished from each other in appearance. They constitute the largest group of vertebrates: there are 22,000 species of fish among the 50,000 species of vertebrates.

Not all animals that live in water are fish. For example, whales are mammals. However, all fish can adapt well to life in water. They move with their fins. Fish has two pairs of fins-pectoral fin and ventral fin, which are located in two parts of the body; There is also a caudal fin, which grows at the tail; And according to different species, there is one or two dorsal fins on the back and a gluteal fin on the hip. They have a bladder filled with gas, called swim bladder, which enables fish to sink, float and keep their position in the water. Only rays and sharks do not have this organ. Fish also have gills for breathing, and most kinds of gills are covered by gill cover bones. Gills are located on both sides of the head and behind the mouth. They are used to filter the water swallowed from the mouth, get oxygen from the water, and then discharge the water from the opening called branchial fissure. The size of different kinds of fish varies greatly. Their bodies consist of three parts: head, trunk and tail. The skin is covered with scales of different sizes and numbers. There is an obvious line on each side called lateral line, which is a sensory organ and is used to determine the direction. The muscles of some teleost fish are separated by some tiny bones.

The first fish that appeared on the earth had a round jawless mouth, and now only 70 kinds of such fish exist, forming jawless fish. Among these fish, lamprey is the most famous. They have no scales and are slender and round, much like eels. The lamprey attaches itself to other fish through a mouth with a sucker and sucks the blood of the host for a living. Other fish are divided into two categories: bony fish and cartilaginous fish.

A bony fish has a pair of bones. There are primitive bony fish in this kind of fish, and only a part of the bones are hard bones. For example, the fish of the suborder Total Fin (including the empty echinodermata), lungfish and sturgeon (such as sturgeon), the difference between these fish and the more evolved teleost is that the bones of teleost are completely composed of hard bones. As representatives of teleost, sea eel, sole and stickleback fish have different shapes, but they all have extremely symmetrical tail fins and are covered with tiny scales (with a few exceptions, including eel and some carp). Bony fish are divided into several types. Eels are some fish whose larvae look very different from adults. Herrings are some fish that live in groups. Carps contain almost all freshwater fish. Perch and tuna are fish whose tail fins are supported by hard spokes. They are called "spiny fins" and constitute the largest group of bony fishes.

Cartilaginous fish has a skeleton composed entirely of cartilage and reinforced by calcium. This kind of fish is mainly sharks and rays.

Eel is a small fish with a flat body when it is born, which is called "Little Eel". When they are mature, they have a long smooth body, generally without scales, and a continuous fin along the back. Eels live in rivers and lakes in Europe and America. They migrate to the algae sea in the northeast of the West Indies in the North Atlantic, where they breed. They die after the cubs are born. On the way back across the Atlantic Ocean, the young eels showed the form of adults, and on the way back, they also began to breed in the the sargasso sea.

Herring lives in the North Sea, the English Channel and the Baltic Sea. Adult fish have a pale belly and a dark blue or nearly black back. Like sardines and herrings, they live in groups, sometimes thousands of fish live together. For each fish, this is an effective self-defense method, because for a predator, only one target can be selected among many fish. When attacked, the fish disappeared almost immediately.

There are thousands of species of carp, almost all over the world. These freshwater fish have large scales, and their teeth are not fixed on their jaws but on their throats. Their mouths can move forward to suck food. Many species of Cyprinus mainly live in calm rivers, small ponds and lakes in Asia and Europe, and their shapes and colors vary greatly. Some species have only a few large scales (mirror carp) or almost no scales (grass carp). These fish are easy to breed, and breeders have created many varieties. Carp mainly feed on plants and invertebrates. The spawning season depends on the temperature of the water, not too cold (at least 20℃). Female fish produce hundreds of eggs, but most young fry become food for other fish and even adult carp as soon as they are born.

Spiny fin appeared about 60 million years ago. Perch is a typical representative of this kind of fish. Their fins are supported by hard and sharp spokes, and their huge tail fins have thorns. Perch live in lakes and rivers in Europe and North America. They eat invertebrates and small fish, including their own young fish. Other species of these fish live in the ocean, such as tuna and swordfish. They are powerful swimmers and can swim 100 km per hour. Tuna can weigh up to 500 kilograms and is a carnivore. Among fish, they have a unique ability to maintain a body temperature higher than the water temperature. Their species include albacore tuna in the Pacific Ocean and bluefin tuna in the Mediterranean and Atlantic Oceans.

Sharks and rays are the main representatives of modern cartilaginous fishes, which may have appeared 4. 1 100 million years ago. As their name suggests, they have a skeleton made of cartilage. Cartilage is a flexible material that hardens when it is filled with calcium, and it is a solid like bone. Chondrichthyes thrive in temperate and hot seas. They breathe through their gills in the water. Gills communicate directly with the outside world through several gill slits behind the head. There are about 550 species of cartilaginous fish, 370 of which are sharks, and the others are basically composed of flat-bodied rays and electric rays.

Fish animals, as experimental research objects or materials in the fields of biomedicine and environmental protection science, have obtained many scientific research achievements all over the world, such as Gordon's research in 1950, Klontz's research in 1968 and Smith's research in 1968. Only in the twelve years before1968, major journals of biological sciences in various countries published 2,500 related reports. In the past 20 years, there have been more relevant literatures. Among the known vertebrate species, there are 30,000 species of fish (estimated to be 40,000 species), 8,600 species of birds, and only 4,500 species of mammals (that is, mice, rats, rabbits, domestic dogs, etc.). It can be seen that the use of fish and animals as experimental materials is indeed an inexhaustible resource, which urges people to widely develop, study and try to apply such rich potential resources.

The selection of fish for biomedical research, especially the toxicological and pharmacological tests of drugs, has many unique advantages: fish are very sensitive to certain drugs and toxic gases, and can cause strong reactions as long as they contain extremely small amounts of ingredients; Taking the pharmacological and toxicological tests of fish as an index, the influence on its habits may be more sensitive; It is suitable to put smaller fish directly into different concentrations; This may be more suitable for the study of some Chinese herbal medicines with low content or weak pharmacological effects that need long-term oral administration; Fish are sensitive to some central nervous system stimulants or inhibitors; The results of fish test method are clear and easy to master; Fish is an economical experimental animal in feeding management.

Up to now, there have been inbred pure fish experimental animals (Gordon's,1950) for more than 20 generations; The development of aseptic fish experimental animals is also being explored (Luckey's, 1936). Fish experimental animals have been widely used in embryology, genetics, endocrinology, toxicology, behavioral science, comparative pathology, environmental protection science and other experimental research fields (Mitruka et al., 1976). Fish animals have some irreplaceable advantages and characteristics, and their biological characteristics can be compared with those of human beings. In China, there are many researches on the subject of fish and its culture, but the research and application of it as an experimental animal are very lacking (Zhu Xishi et al., 1960, 1962).

There are many achievements in the application of fish experimental animals. Fish animals (especially small freshwater fish) have been used in cancer research in the field of oncology, and a lot of observation and experimental work have been done. It is known that all tissues of freshwater fish will have neoplasia, and its clinical course and morphological manifestations are similar to those of other vertebrates (including humans). Therefore, fish experimental animals have become indispensable materials in experimental oncology, especially in comparative oncology and the exploration of suspected carcinogens in the environment (especially in water sources). In fact, the research on fish oncology has gone through the stages of systematic classification and experimental analysis, and has reached a new stage of prevention and treatment research (Squire et al., 1978), with broad prospects.

The application of goldfish (Carassius Auratus Linnaeus) in biomedical research has been reported. Diethylnitrosamine was put into goldfish bowl water (below 120ppm) for 4 months, and after 6 months' storage, it was found that 13 tail animals developed liver cancer; In addition, precancerous cell lesions (Bannsch, 1976) appeared in the liver of four fish. The livers of animals in the control group were all negative. It is suggested that it is possible to use goldfish as an experimental animal to establish an induced tumor model.

Fish has a unique use in toxicology. Fish are often selected for acute toxicity experiments. When conducting such experiments, various experimental conditions must be strict before and during the experiment: representative experimental fish in this area must be selected, which is sensitive to harmful substances. Bait organisms must also meet the experimental requirements. Try to keep the concentration of harmful substances in water stable during the test, and try to find toxic reactions in the specified concentration. When conducting toxicity test, it is required that the average body length of freshwater fish, marine freshwater fish or marine fish should be below 50 mm. The newly collected fish should be domesticated for less than a week until it gradually adapts to the experimental conditions. During the domestication process, the feeding amount should be less, and the feeding should be stopped 2 days before the experiment. The mortality and morbidity of domesticated fish must be above 10% within 4 days before the experiment. The water temperature is kept within a certain range. Warm-water fish require 20 ~ 28℃, cold-water fish keep12 ~18℃, and the general variation range should not exceed 4℃. In each experimental concentration group, if more than 10 fish are released, the water in the experimental tank should be continuously changed by using the running water test device, and the water should be changed 6 ~10 times a day. If the static water test method is adopted, the experimental concentration should be kept below 1 g per 1 liter of fresh water; The seawater body should be kept below 0.3g, and all the water should be replaced at least once every 24 hours, and the logarithmic intervals of 100, 75, 56, 42, 32, 24, 18, 13.5 and10ml/l should be selected. Exploratory experiments should be carried out first, and the primary concentration must include the concentration with a mortality rate of about 50% within 24 ~ 96 hours. The dissolved oxygen content in experimental water should not be less than 4 mg/L for warm-water fish; Cold water fish shall not be less than 5mg/L.. To test whether the fish is dead or not, tap the handle of the fish tail with a glass rod. If the fish does not move, it is judged to be dead. It is required to set up a control experiment at the same time. When the number of dead fish in the control group exceeds 10% or there are unhealthy fish, the experimental results obtained cannot be used.

Macropolecs Opercularis in Qishan or Betta Splendens in Thailand are sensitive animals to determine the inhibition of instinctive behavior by drugs. Betta grows in Southeast Asia, and there are feeding supplies in Guangdong Province of China. The feeding temperature is 27 ~ 29℃. If tap water is used when feeding, it should be placed in the open air for more than 24 hours, and undiluted drugs should be avoided to poison rabbits and fish by drinking high-concentration drugs. Female fish and male fish don't fight when they live in groups. When feeding, if the mature male fish isolated for one day meets another male fish, a fighting action will occur. If two male fish are raised in square glass jars respectively, and the middle of the two jars is separated by cardboard, when the cardboard is removed, the gill covers of the two fish can be seen to open, spread the dorsal fin and caudal fin and impact each other. If chlorpromazine hydrochloride is put into the pot with a content of 2 mg/L, the fighting action of betta can be terminated. If a drug can inhibit instinctive behavior, it can prevent two bettas from fighting. Some people divide it into five periods according to the degree of action of drugs to inhibit fighting of betta fish: 0 period is not to inhibit fighting; 1 period is taming, suppressing fighting action and feeding as usual; The second stage is imbalance or sideways; The third stage is anesthesia, sideways, and the reaction to contact is slight or disappeared; Stage 4 is death.

Catfish (Catfish) has no power generation organ, but it has sensitive electrical sensation. Four electrical sensation centers have been found, namely, the posterior linear lobe of the medulla oblongata, the posterior lobe of the cerebellum, the semicircular process of the midbrain and the pronucleus. It is suitable for studying the response of electric sensory center to static and dipole electric fields.

The catfish is15 ~ 20 cm in length, and the temperature is lowered (1~ 4℃) to anesthetize it. Then a small hole is made in the top of the head to expose the brain to be recorded. After the operation, 0.5mg/kg of tuba curculicidae is injected intramuscularly, and the catfish is sunk into the experimental tank, only the surgical site is exposed to the water, and water containing saturated air is introduced into the mouth with a latex tube for artificial operation.