Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Filter feeders can be sessile, planktonic or nektonic, and some extant animals that rely on this method of feeding are clams, krill, sponges, baleen whales and many fish. Some birds, such as flamingos and certain species of duck, are also filter feeders. Filter feeders can play an important role in cleaning water, and are therefore considered ecosystem engineers. They are also important in bioaccumulation and, as a result, as indicator organisms.

A fish is an aquatic, anamniotic, gill-bearing vertebrate animal with swimming fins and a hard skull, but lacking limbs with digits. Fish can be grouped into the more basal jawless fish and the more common jawed fish, the latter including all living cartilaginous and bony fish, as well as the extinct placoderms and acanthodians. Most fish are cold-blooded, their body temperature varying with the surrounding water, though some large active swimmers like white shark and tuna can hold a higher core temperature. Many fish can communicate acoustically with each other, such as during courtship displays.