Rainbow trout is commonly known as squat fish. Originally from California, USA, it is mainly distributed in the sea area between Mexico and Alaska, and has been introduced to Oceania, Southeast Asia, Europe, Japan and North Korea. 1959 is the first time that North Korea was introduced into China. It was first cultured in freshwater ponds and then domesticated, which is one of the objects of seawater cage culture. The fish is tender in meat, rich in fat and delicious in taste, and it is an excellent fish species favored by people. Bows are slender spindles. The head length accounts for about 20% of the total length. The mouth is big, the upper and lower teeth are developed, and the gill rake is of medium length. Sexually mature individuals have a wide and bright rainbow band along the middle of the lateral line, hence the name. Males have smaller heads and taller bodies than females. The mandibular curve of male fish increases with age. The back of the young fish is blue-green, the sides are silvery white, the ventral surface is white, and there are 5 ~ 10 longitudinal stripes between the head and the caudal fin. The markings of adult fish disappear and spots appear (Figure 25).

Rainbow crouches in the natural environment, often inhabiting the waters with clear water quality and gravel bottom. It is a cold-water fish, but it can tolerate higher water temperature than other cold-water fish. The domestic water temperature is 3 ~ 24℃, and the suitable temperature is 10 ~ 18℃. The optimum growth temperature is 14 ~ 18℃, and the fastest growth is around 17℃. This kind of fish is an aerobic fish with high countercurrent. It is best to cultivate in running water and cages, which consumes a lot of oxygen. When the dissolved oxygen in water is less than 5 mg/L, it is uncomfortable. The adaptability to salinity increases with the growth of individuals. The salinity adaptation range of juvenile fish is 0.5% ~ 0.8%, that of current fish is 65,438+0.2% ~ 65,438+0.4%, and that of second instar fish is 2% ~ 2.5%. Crocodiles mainly eat larvae and adults of Trichoptera, Coleoptera and Odonata. Also eat tadpoles, chironomid larvae, small fish and shrimps. They also eat leaves and seeds of aquatic plants. Under the condition of mariculture, small miscellaneous fish, shellfish, etc. , and can throw mixed bait. Growth is greatly influenced by water environment and food. About100g of fish is released in the coastal areas of Shandong Province from September to June, and about 500g of commercial fish can be farmed in April to May of the following year. The second-instar fish has the highest growth rate. The life span of this fish is generally 8 ~ 1 1 year, with an individual of 7.5 kg and a maximum of 20 ~ 25 kg. The age of sexual maturity is generally 3 ~ 5 years old, and the male fish is one year earlier than the female fish. The spawning season varies with region and temperature, and usually spawns around the Spring Festival. Usually found on gravel beaches of small rivers. During the breeding season, males will fight with each other. Female fish dig spawning pits and male fish protect them.

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