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Brief introduction of mullet
Snakehead, also known as snakehead, raw fish, snakehead, talented fish, etc., belongs to the order Perciformes, snakehead. In China, there are two genera of Ophiuchus: Ophiuchus and Ophiuchus. There are 7 species of snakehead (and Heilongjiang subspecies), spotted snakehead, snakehead, eye snakehead, spotted snakehead, snakehead and striped snakehead in the genus snakehead. There is only one species of Channa in the genus Channa. At present, snakehead and spotted snakehead are the breeding objects.

Snakehead is mainly distributed in the Yangtze River basin and the area as far north as Heilongjiang, especially in Hubei, Jiangxi, Anhui, Henan, Liaoning and other provinces. It is also found in the south of the Yangtze River basin, but it is rare. The Heilongjiang subspecies of ophiocephalus argus are mainly distributed in the southern part of Heilongjiang River Basin, Wusuli River Basin, Xingkai Lake, Songhua River and other swamp areas. The spotted snakehead is distributed in the south of the Yangtze River basin, especially in Guangdong, Guangxi, Taiwan Province, Fujian, Yunnan and other places.

Ophiocephalus argus is very popular in domestic and foreign markets because of its tender meat, delicious taste and high nutritional value, and it is a favorite excellent dish. In addition, the anchovy also has the medical effects of removing blood stasis, promoting tissue regeneration, nourishing and recuperating, strengthening the spleen and promoting diuresis. After illness, postpartum and hand surgery, it has the functions of promoting granulation, enriching blood and accelerating wound healing, and can also treat edema, dampness, beriberi, hemorrhoids, scabies and other diseases.

Snakehead is not strict with the external environment, and has strong adaptability to life, even in the water with insufficient dissolved oxygen. In recent years, with the development of domestic aquaculture and the need of foreign trade, mullet has gradually become a special breed, and its breeding technology has begun to attract people's attention.

Second, biological characteristics

(A) morphological characteristics

The front part of mullet body is cylindrical, and the back part is flat. The head is long, slightly flat at the front and slightly raised at the back. The kiss is short, round and blunt, with a large mouth, an end position, a slightly oblique mouth crack, and a slightly protruding jaw. The teeth are small and banded in the upper and lower jaws, and the teeth on both sides of the mandible are firm. Small eyes, upper position, in the first half of the head, quite close to the snout. There are two pairs of nostrils, the front nostril is tubular at the snout and the rear nostril is a small round hole above the eyes. The branchial cleft is large, the left and right branchial membranes are healed, and the branchial harrow is short and sparse, and there is an auxiliary branchial organ above the branchial cavity.

The color of snakehead is grayish black, the color of its back and head is darker, its abdomen is pale, there are irregular black patches on its side, and there are two rows of black stripes on its head. The odd fin has black and white spots, and the lateral fin is grayish yellow with irregular spots.

The snakehead fish is covered with medium-sized scales, round scales and irregular scales on the top of its head. The lateral line is straight, with a slight twist above the anus, moving down two rows of scales, running in the middle of the body and extending to the caudal base.

The dorsal fin of snakehead is quite long, almost connected with the caudal fin, without hard spines, starting above the base of pectoral fin and close to the snout. The ventral fin is short, starting below the 4th-5th fin of dorsal fin and ending short of anus. The pectoral fin is round, and the tip of the fin extends beyond the middle of the ventral fin. The gluteal fin is shorter than the dorsal fin, and the starting point is below the 15- 16 fin of the pain fin. The caudal fin is round. The anus is located immediately in front of the anal fin.

The snakehead swim bladder is single-chambered, slender, with a round front end and a sharp end extending above the base of the gluteal fin. The stomach is cystic, with two pylorus, which are thick and long, and are about intestine 1/3. The intestine is short and hyperbolic, longer than half of the body length.

The Heilongjiang subspecies of snakehead is mainly characterized by dark green-black back, irregular black-green side, dorsal fin and caudal fin with the same color as back, and light pectoral fin and anal fin.

The main differences between snakehead and spotted snakehead are: snakehead body is longer and spotted snakehead bowl is shorter; There are also obvious differences in the markings on the top of their heads: there are seven-star markings on the top of snakehead's head, while the markings on the top of spotted snakehead's head are similar to those of "188"; In addition, the head of snakehead is longer and sharper, more like a snake.

(2) Living habits

Snakehead is a benthic fish, which usually lives in still water or micro-flowing water with overgrown aquatic plants and soft sediment, and is distributed in lakes, rivers, reservoirs, ponds and other waters. Often dive to the bottom of the water to swing its pectoral fins to maintain body balance.

Mullet has strong adaptability to the changes of environmental factors in water, especially to hypoxia, water temperature and poor water quality. When the water is short of oxygen, it can keep its head out of the water. With the help of the suprabranchial device, which is composed of the upper branchial bone on the back of the first branchial arch and the bone piece extended from the glossopharyngeal bone, the oxygen in the air can be directly breathed. Therefore, it can survive for a long time even in humid areas with little water and no water. The survival water temperature of mullet is 0-4 1℃, and the optimum water temperature is 16-30℃. When the water temperature reaches above 8℃ in spring, it often moves in the upper and middle layers of water. Summer season is active in the upper layer of water; When the water temperature drops below 6℃ in autumn, it swims slowly and often lurks in the depths of water; When the water temperature is close to 0℃ in winter, it will stay in the bottom mud and stop eating.

Mullet has a strong jumping ability. When the weather is sultry and rainy and the water rises, mullet often jumps out of the water and escapes along the pond bank. When there is a running water impact, it will also arouse the fish to jump and escape. If the bait in the pond where he lives is insufficient, he will also move to other ponds, and his body will move forward slowly like a snake when moving.

(3) Feeding habits

Mullet is a fierce carnivorous fish, and it is gluttonous. The prey varies with the size of the fish. Larvae with a body length of less than 3 cm mainly feed on scratching feet, cladocera and chironomid larvae, while those with a body length of less than 3-8 cm feed on larvae, tadpoles, shrimps and larvae in aquatic insects, while adult fish with a body length of more than 20 cm prey on various small fish and frogs (small fish mainly refer to crucian carp, rice sticks, red-eyed trout, loach and various domestic juveniles). The mullet swims fast, but generally does not prey. Snakehead has a large food intake, and can often swallow live bait about half of its body length, and the maximum capacity of its stomach can reach 60% of its body weight. According to anatomy, a 500-gram snakehead swallowed 8 grass carp species 10 cm long in a short time. Snakehead also has the habit of killing each other, and can devour similar individuals whose body length is less than two-thirds of their own. Its food intake is closely related to the water temperature. When the water temperature is high in summer, it is quite gluttonous and eats a lot; Stop eating when the water temperature is lower than 12℃.

Under the condition of artificial feeding, when animal feed is insufficient, we can also feed on artificial compound feed such as bean cake, vegetable cake and fish meal.

(D) Age and growth

The growth rate of snakehead is quite fast, but the growth rate of snakehead and spotted snakehead is not the same in different regions and different environments.

The fry of snakehead hatched in that year can reach 1 5cm and weigh about 50g at the end of the year. According to the specimens collected in Taihu Lake, the body length and weight of each age group are1winter fish body length14.2-19.2cm and weight/kloc-. 2 The winter fish is 24-28 cm long and weighs 350-760 g; The winter fish is 32. cm long and weighs 605-1000g.

The growth rate of Mylabris argus at all ages is 1 winter fish length 19.0-39.8 cm, and its weight is 95-760 g; 2. The length of winter fish is 38.5-45.0g, and the weight is 625-1395g; 3 The winter fish is 45.0-59.0 cm long and weighs 1467-203 1 g.

Under the condition of artificial rearing, the individual weight can reach 250 grams in the current year and 500- 1000 grams in the next year.

(5) Reproductive habits

The spawning season of mullet varies with different climatic conditions in different places. In South China, it is from mid-April to mid-September, with the peak in May and June. The middle region is from May to July, and it is concentrated in June. The breeding water temperature is 18℃-30℃, and the optimum water temperature is 20℃-25℃.

The sexual maturity age of mullet varies slightly in different regions. In South China, the gonads of 1 winter fish, which are usually more than 20 cm in length, are mature, while in the Yangtze River basin, it takes 2 winters and 30 cm in length to lay eggs. Snakehead can naturally breed in ponds, rivers and reservoirs, and the spawning grounds are generally distributed in shallow waters with lush aquatic plants. The amount of eggs conceived and laid is related to the size of parents. The fecundity of snakehead is usually about 20,000-30,000 eggs per kilogram of body weight. The fecundity of 0.5 kg of snakehead is generally 0.8- 1 10,000 eggs, and individual can reach1-10.2 million eggs.

The way of spawning is to build a nest. Before spawning, the sexually mature male and female fish swim in the spawning site in pairs, and * * * use the same mouth to collect aquatic plants, plant fragments and spit foam to build a fish nest with a slightly ring shape and a diameter of about 0.5- 1 m, which floats on the water surface. After the nest is built, before sunrise in a calm morning, the female and male fish chase each other and estrus, and then the female fish. Fish spawn many times. After spawning, the parent fish stays at the bottom of the nest to protect the fish eggs from infringement.

The eggs of mullet are golden yellow with oil balls, which are floating eggs with a diameter of about 2 mm. The egg diameter of Siniperca chuatsi subsp. Heilongjiang is slightly smaller, about 1.5 mm. The incubation time of sperm eggs is related to the water temperature: when the water temperature is low, the incubation time is longer; The higher the water temperature, the shorter the incubation time. The newly hatched fry is 3.8-4.3 mm in length, with melanocytes all over the body, pectoral fin primordia appearing, oil balls and yolk sacs making the body swell obviously, with the appearance of tadpoles, often lying on the side and floating near the water surface, with poor exercise ability, and relying on the absorption of yolk. When the seedling is 6. 1-6.2 mm long, pectoral fin, branchial fissure and mouth have all appeared, and the oil ball in the yolk moves to the abdomen, often lying on its back on the water surface, and can make short-distance vertical movement downward. When the seedling is 7.4-7.5 mm long, the whole body is black, the yolk sac disappears, and the parent fish begins to eat.