The four major species of carp refer to artificially raised herring, grass carp, silver carp and bighead carp. It is a fish species that has been selected for polyculture and high yield in pond fish farming in China for more than 1,000 years. Silver carp is also called silver carp. It moves in the upper layers of the water and eats green algae and other phytoplankton; bighead carp has a larger head and is commonly known as "fat-headed fish" and also called silver carp. They live in the middle and upper layers of the waters and eat protozoa, water fleas and other zooplankton; grass carp lives in the middle and lower layers of the waters and feed on aquatic plants; herring lives in the bottom of the waters and eats molluscs such as snails, clams and mussels; these four species of fish Mixed feeding can improve the utilization rate of bait and increase fish production.

So choose: A