The warmouth is a sunfish species that is synonymous with lakes and ponds. It is rarely found in river lakes, overflow ponds or oxbows. There is some speculation that there are longitudinal differences in the distribution and abundance of warmouth in southern Iowa. Warmouth are common in the southeastern lakes and rare in the southwest. The reason for this occurrence is unknown.

The warmouth is a thick-bodied, stout-appearing sunfish with a rich olive-brown color on the back and sides. The sides are covered with dark brown mottlings, and the belly is light yellow. A characteristic feature is 4 or 5 reddish-brown streaks radiating from the eye across each side of the head. The iris of the eye is red, and the fins are spotted with dark brown, forming bands which are more prominent on the soft parts of the dorsal and anal fin. The warmouth can be easily distinguished from the other sunfishes by the patch of small teeth on the tongue. Most often this fish is confused by fishermen with the rock bass, but they are easily separated by counting the spiny rays in the anal fin; the warmouth has 3 spines, and the rock bass has 6 spines. The spiny dorsal fin, which is broadly connected with the soft part of the fin, contains 10 spines.

Warmouth are sight-feeders that consume largely insects, crayfish and fish that they prey on in the soft-bottomed, weedy areas that they prefer for habitat. The young feed heavily on zooplankton and insects that are abundant in these locations.

Warmouth, like all members of this family, reproduce by constructing a nest for egg deposition. Nest building begins in mid-May and peaks in early June, but spawning may extend into August. Nests are built near underwater structures, a stump or clumps of vegetation but seldom on clean sand. The nests will be separated unless sites are limited; then they may adjoin each other. Most nests are constructed in 1 1/2 to 4 feet of water. The nest is constructed and guarded closely by the male until the fry depart. The male is very aggressive in his territory, approaching all intruders with flared gills, open mouth and blood red eyes. Eggs hatch in about 3 days, and the fry leave the nest in 5 to 6 days.

Young warmouth reach 1 to 2 inches in length by autumn and attain maximum size of about 7 to 8 inches by the fifth year of life. There is no record-size warmouth in Iowa, but the largest fish listed elsewhere was over 11 inches in length.

*Mayhew, J. (editor). 1987. Iowa Fish and Fishing. Iowa Department of Natural Resources, Des Moines, Iowa. 323 pp.