It is a gregarious animal. Bighead fish generally refers to bighead carp (Cyprinidae, Genus Bighead), a freshwater fish, which lives in the middle and upper layers of rivers, gentle bends, lakes and reservoirs. It is a typical plankton-eating fish with zooplankton as its staple food and phytoplankton as well. Cod is a marine fish, mostly cold-water fish living in the bottom of the ocean and the middle and lower layers of the deep sea. Like to live in groups, usually inhabiting the sea area with water depth of15-250 m.