Snakehead belongs to Perciformes, Heracleidae, commonly known as mullet, herring, snakehead, etc. It is a valuable freshwater economic fish with large size, fast growth and high economic value among Heracleidae. Snakehead has less bone spurs, high meat content and rich nutrition, which is higher than protein contained in chicken and beef. According to the determination, every 100g of snakehead meat contains 19.8g of protein, 1.49g of fat and 1.2g of carbohydrate, and is rich in nutrients such as calcium, phosphorus, iron and zinc needed by human body. As a medicine, snakehead has the effects of removing blood stasis, promoting tissue regeneration, nourishing and recuperating, etc. After surgery, snakehead can promote granulation, enrich blood and promote wound healing. Therefore, snakehead has always been welcomed by Southeast Asian countries and Hong Kong and Macao markets, and is one of the important aquatic products exported by China. The artificial culture of snakehead in China has just begun, and its prospect is promising, but there are still many problems to be solved urgently. The biological characteristics and culture techniques of snakehead are described as follows: 1. Biological characteristics of snakehead 1. Morphological characteristics The snakehead has a long cylindrical body, a snake-like tip and a round and flat tail. The upper and lower jaws are all thin, and there are canine teeth on the plough bone and palate bone, and the branchial fissure is large, which is not connected with the cheek. The branchial harrow is thick and short, and the arrangement is sparse. There are developed suprabranchial organs in the suprabranchial cavity, which can directly exchange gas. Therefore, the snakehead will not die as long as its gills and body are kept moist for 2 ~ 3 days, which is convenient for transportation. The snakehead is covered with round scales, its head and back are dark black, its abdomen is gray, and there are two rows of large irregular black spots on its side. Dorsal fin and gluteal fin are very long, including 47 ~ 52 dorsal fin strips, 31 ~ 36 gluteal fin strips, 17 pectoral fin strips, 1 ~ 5 ventral fin strips, 6069 lateral line scales, and 52 ~ 60 spine push bones. The body length is 53 ~ 6.2 times of the body height, 3.0 ~ 3.3 times of the head length, and the tail handle length is 0.6 times of the tail handle height. 2 Living Habits Snakehead likes to live in rivers, lakes, reservoirs, ditches, harbors and still water and grass areas in low-lying swamps. Snakehead is particularly adaptable to water quality, water temperature and other external environmental changes, and it can live even in the water environment where other fish are difficult to live. The survival water temperature of snakehead is 0 ~ 41℃, and the optimum water temperature is 26 ~ 28℃. When the water temperature is too low in winter, the latter half of its body is submerged in mud or hay, and its head is exposed in the water, so it can survive without eating or moving. Ophiocephalus argus is resistant to hypoxia and can survive in turbid and anoxic water. It leans its head out of the water and directly breathes oxygen in the air with the help of branchial organs. Even in the case of little water or even water, it can survive for a long time as long as the gill and body surface are kept at a certain humidity. Snakehead is good at jumping and easy to escape. A 800-1000 g snakehead can jump 1-2 m above the water. In rainy season, when food is insufficient or other conditions are not suitable, snakehead often jumps out of the water, resulting in "aisle" phenomenon. Therefore, it is necessary to pay attention to the prevention and escape of snakehead breeding. 3. Feeding habits and growth snakehead is a typical fierce carnivorous fish, which mainly feeds on small fish, shrimp, frogs and tadpoles, wild insects and other aquatic animals. Due to the different sizes and habitats of fish, the types of food they eat are different. In the fry stage, copepods, cladocera and chironomid larvae are the main food. When the body length is over 30 mm, aquatic insects is the main food, and some small fish and shrimp are also eaten. When the body length is over 80 mm, fish and shrimp are the main food. It is worth noting that with the growth of fish, snakehead has the habit of killing each other when the food is insufficient or the size is very different. Therefore, it is necessary to pay attention to the consistency of stocking specifications for snakehead, especially in the stage of fry cultivation, and multi-level sub-culture should be carried out according to the size. Under natural conditions, the growth of snakehead is accelerated before the 2nd instar, and it grows vigorously. After the 2nd instar, it enters the stage of sexual maturity, and the growth rate of fish slows down. Under the condition of artificial feeding, the fry of snakehead can reach 200 ~ 300 g/tail, and the second-instar fish can reach 1500 ~ 2000 g/tail. 4. Sexual maturity age and breeding season The sexual maturity age and breeding season of ophiocephalus argus vary slightly with different regions. The gonad of ophiocephalus argus in the Yangtze River basin can mature when it is 2 winter years old and over 30cm long, and its spawning season is from May to July, with the highest spawning season in June. The ophiocephalus argus in Heilongjiang river basin can mature only when it is over 2 winter years old and its gonad is over 35 cm long. Its spawning season is from June to August, and its spawning peak is in July. Second, the breeding of snakehead fry With the development of snakehead breeding, the demand for snakehead fry will be increasing. Only catching wild fry for breeding is not only a small number, but also a poor quality and irregular specifications. Therefore, artificial propagation of snakehead fry has become an inevitable trend. 1. Selection and cultivation of parent fish of snakehead (1) The source of parent fish of snakehead and the source of choosing parent fish of snakehead are mainly in two aspects: one is to select and keep parent fish in combination with winter fishing in rivers and lakes; The second is to cultivate and select parent fish in ponds. The main criteria for selecting and retaining parent fish are: strong physique, no disease or injury, weight above 750g, 2 winter age, sexual maturity, and the ratio of female to male is 1 ∶ 1. 2 Parent fish breeding pond for snakehead: The area is generally 300 ~ 400 m2, which should not be too large. The water depth is 1.2 ~ 1.5 m, and the bottom of the soil pond is provided with a nylon net with a height of 0.8 ~ 1 m to prevent snakehead from fleeing. Before stocking, each acre of pond is disinfected with 50 ~ 60 kg of quicklime. Parent fish stocking: There are a large number of parent fish, which can be raised alone, with 8 ~ 10 groups per 100 square meters, and appropriate silver carp and bighead carp species are raised to adjust the water quality. Feed feeding: the main feed for feeding the parent fish of snakehead is small fish and shrimp, which can be fed when the water temperature reaches above 18℃, and the food intake increases greatly when the water temperature is 23 ~ 27℃, and the feeding amount is 10% ~ 15% of the parent fish's weight. The small fish and shrimp fed should be fresh and palatable in size. Feeding management: mainly pay attention to the pre-natal and post-natal cultivation of parent fish, and often add micro-running water to keep the water fresh. In addition, aquatic plants such as water hyacinth or water peanuts are planted in the center or around the parent fish pond to facilitate snakehead hiding, feeding and regulating water quality. 2. Artificial spawning (1) Preparation of spawning ponds and fish nests. The spawning pond for snakehead is preferably a earthen pond, which does not harm the parent fish, with an area of 20 ~ 30m2 and a water depth of 1.2 ~ 1.5m. Before spawning, the pond should be thoroughly cleaned and disinfected with quicklime to eliminate harmful organisms such as wild fish and frog eggs, and it should be well fenced to prevent other animals from entering. Snakehead has nesting habit, so the spawning pond can be made of soft, fresh and nontoxic water hyacinth, water peanut or POTAMOGETON malayi, and put into the spawning pond after the parent fish is injected with oxytocin. (2) Drugs and methods for inducing spawning There are many kinds of drugs for inducing spawning of snakehead. In practical production, two carps+HCG 1000 ~ 1500 IU/kg or DOM+HCG 1000 ~ 1500 IU/kg are commonly used, and the dosage of male fish is 1/2 of that of female fish. The injection is divided into two times, the first injection is 1/3 ~ 1/4 of the total amount of the drug to promote the further maturation of gonads, and the second injection is given after 15 ~ 20 hours. The site of injection is generally the base of pectoral fin, which is injected into body cavity. (3) Pairing of parent fish and spawning After the parent fish is injected with oxytocin drugs, according to the individual size, the females and males are paired in 1: 1 and put in spawning ponds, and 1-2 pairs should be put in each spawning pond, so as to prevent "courtship struggle" from affecting the rate of spawning. When the water temperature is 20 ~ 25℃ and the effect time is 25 ~ 30 hours, eggs can be laid. Keep quiet when the parent fish is in estrus and lays eggs. 3. Incubation of fertilized eggs After the parent fish lays eggs, the fertilized eggs are hatched in time. There are various ways to artificially incubate the fertilized eggs of snakehead, which can be used flexibly according to the actual situation. (1) Incubation in spawning pool: after spawning, only the parent fish are fished out, and the fertilized eggs continue to hatch in the spawning pool. It should be noted that the incubation pool is kept in a micro-flow state and fresh water is constantly replaced. In addition, attention should be paid to prevent other fish and frogs from entering the pool. This method is time-saving, labor-saving, low-cost, the fertilized egg is not damaged, and the hatching rate is high, so it is suitable for production in every household. (2) Incubation loop incubation: move the fish nest together with fertilized eggs into the incubation loop for centralized incubation, and put 20,000 ~ 30,000 fertilized eggs in each cubic meter of water, with the impulse of running water, and pay attention to washing the screen window frequently to prevent flooding. The advantages of this hatching method are that the fertilized eggs are concentrated and easy to manage, which is suitable for large hatcheries. (3) Cage incubation: move the fish nest and fertilized eggs into the cage together. The place where the cage is set requires fresh water, no pollution, and a certain amount of running water, with 10,000 ~ 12,000 eggs per cubic meter of water. Cage incubation is easy to operate and easy to manage, which is suitable for both a small number of hatcheries and a large number of hatcheries. 3. Feeding habit domestication and fry cultivation of snakehead The feeding habit domestication and fry cultivation of snakehead is a major technical difficulty in artificial culture of snakehead. It is generally reflected in all places that "snakehead is easy to seedling and difficult to breed". The highest survival rate of flowering is only 50% ~ 60%, generally 20% ~ 30%, or even lower. Therefore, it is an urgent technical difficulty to improve the survival rate of snakehead fry cultivation and reduce the production cost. 1. Domestication of larvae The newly hatched larvae are weak in constitution and poor in mobility, floating on the water surface or lying on the side of aquatic plants and other attachments, and take their own yolk as the source of nutrition. As the yolk sac is gradually absorbed and shrunk, the larvae develop continuously, their mobility is enhanced, they can swim freely, and they begin to take the initiative to feed and take mixed nutrition. At this time, the death of snakehead larvae is the peak, so it is necessary to domesticate them carefully. Its domestication method is as follows: (1) Feeding in time. When the yolk sac disappears and the fry feed from the outside, the plankton is fished out with a plankton net, filtered with a 30-40 mesh sieve for 2-3 days, and the filtrate is evenly spilled in the incubator. If the food still cannot meet its needs, the cooked yolk can be fed, with 1-2 cooked yolks for every 10,000 fry, filtered with a 30-40 mesh sieve, and the filtrate is evenly spilled in the incubator. (2) Keep the water fresh. After the fish fry are demoulded, a large number of egg membranes and oils float in the water or sink to the bottom of the water, so a certain amount of micro-flow water should be kept frequently to increase dissolved oxygen in the water and eliminate egg membranes and oils. (3) Pay attention to disease prevention. Ophiocephalus argus is the most susceptible to water mold at the fry stage, and it is generally disinfected with 0.1 ~ 0.2g/m3 malachite green water. After 8 ~ 10 days of domestication, the fry can reach 10 ~ 15 mm in length and turn yellow. With the increase of fry size and density, the demand for bait and dissolved oxygen also increases. At this time, it should be transferred to seed cultivation in time. 2. Fish seed cultivation (1) Cultivation of fry in earthen pond ① Requirements for fry pond: It is better to cultivate fry of snakehead in earthen pond, with an area of 50 ~ 100m2 in general, so as to facilitate feeding, operation and management. Before stocking the fry, drain the pond water, thoroughly clean the pond with quicklime and apply sufficient base fertilizer to improve the water quality, so that the fry can eat food when they go into the pond. (2) fry stocking: before fry stocking, put 20 ~ 30 test fish to see whether the medicinal properties of the water body have disappeared. The released fry should be hatched in the same batch, and the temperature difference of water during stocking should not exceed 2℃. The stocking density depends on bait, culture technology and culture specifications, and the general stocking density is 60 ~ 80 fish/m2. After that, the fry will be gradually screened and diluted according to the growth situation and cultivation time. Others put 40 ~ 50 fish/m2 at a time, and directly cultivate large-scale fish species. ③ Feed feeding: Domesticated larvae feed on zooplankton when they go into the pond. As the fry grow up, the food intake increases, while the zooplankton in the pond gradually decreases. At this time, on the one hand, plankton can be cultivated by continuing fertilization, on the other hand, soybean milk can be added. After 15 ~ 20 days' cultivation, when the fry is more than 3 cm, its feeding habits begin to change, and its food intake is further increased. Zooplankton alone can no longer meet its growth needs. At this time, minced fish can be fed on the dining table for taming, and a small amount of artificial compound feed is added to mix minced fish after 2 ~ 3 days, and then the proportion of artificial compound feed is gradually increased, and the consumption of minced fish is reduced until all artificial compound feed is used. ④ Cultivation management: A. Timely mediation of water quality. In the process of fry cultivation, due to fertilization and baiting, the remaining manure residue baits are the most likely to deteriorate the water quality. Therefore, during the fry cultivation of ophiocephalus argus, the water should be changed every 2 ~ 3 days, and the amount of water changed each time is 1/3 ~ 1/4 of the pool water, and the water should be drained first and then irrigated. In addition, some aquatic plants such as water peanuts or water hyacinths are transplanted in the fry pond to purify the water quality and provide shelter and food for the fry. B. Separate feeding in time. When there is a big difference in fry growth specifications, snakehead has the habit of eating big and eating small, especially when food is lacking. Therefore, snakehead fry cultivation should be timely hauled, screened and separately raised, and the fry in the same pond should be of the same size to avoid the law of the jungle.