The "four major fish", herring, grass carp, silver carp, and bighead carp, are the fish species that have 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 waters and eats green algae and other phytoplankton; bighead carp has a larger head and is commonly known as "fat-headed fish", also called silver carp. It lives in the middle and upper layers of the waters and eats protozoa, water fleas and other zooplankton; grass carp lives In the middle and lower layers of the water, they feed on aquatic plants; herring inhabits the bottom of the water and eats molluscs such as snails, clams, and mussels. Mixed feeding of these four kinds of fish can improve the utilization rate of bait and increase fish production.

So the answer is: grass carp, silver carp, bighead carp.