A parasitic species, the chestnut lamprey is fitted with numerous strong, sharp teeth for grasping and piercing the body of a host. It is ideally suited to feed off body fluids of other fishes. However, only the adult can feed in this fashion. The juveniles, called ammocoetes, have mouth parts that form a sieve to feed on minute plankton. The chestnut lamprey reaches a length of about 13 inches and can be found throughout the upper Mississippi River Valley drainage.
Many fish eat both plants and animals and are classified as omnivorous feeders.
An example is the hornyhead chub, a member of the cyprinid or minnow family. This widemouthed species feeds at any depth on flora and fauna of clear water creeks and smaller rivers. Items as large as small crayfish are eaten. This unspecialized fish is rather common in Wisconsin streams, and reaches a maximum size of a little over eight inches. This highly specialized member of the cyprinid family is a bottom dwelling species.