The speckled chub seldom exceeds three inches in length and is considered to be threatened in Wisconsin. Plankton are very tiny plant and animal organisms, a preferred food for many juvenile fish and some adults. The paddlefish is uniquely adapted to filter such organisms out of the water as it swims along with its mouth open. Often shaking its head, the fish will engulf a vast amount of water to strain out the food. Other bottom dwellers grab free floating food as it comes by rather than sucking it up from the bottom.
Examples are the mottled sculpin and blackside darter.
The mottled sculpin has an exceptionally large mouth that allows it to feed on both mature and immature aquatic insects and, occasionally, on unwary small fish. Common in streams and lakes, it reaches four inches in length. The blackside darter has a much smaller mouth and must eat smaller prey, with mature and immature insects and crustaceans desirable foods. About four inches in length, it lives in small rivers throughout Wisconsin. These fish have another adaptation for living on the bottom.