In other words, koi fish will cross with wild natural carp. In the long run, natural carp genes will be mixed, thus threatening the purity and survival of local carp. Among domestic pets, besides koi fish, there are other animals that can't be kept at will, such as Brazilian tortoise, mosquito-eating fish, scavenger, crocodile turtle, bullfrog, tilapia and finch eel.
Red carp will appear in carp herds all over China and can live in various waters. On the basis of red carp, the bred varieties are glass red carp, purse red carp, Xingguo red carp, Qingjiang red carp in Hubei and Oujiang colored carp in Zhejiang.
Koi fish was bred by the Japanese on the basis of red carp imported from China, and has become the national fish of Japan. Red carp is the main breeding object, which breeds all year round, and the yield is high in spring and autumn.