The warmouth is a thick-bodied, stout-appearing fish 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 other sunfi
The warmouth is found throughout the Mississippi River and has been rarely taken in the lower reaches of its tributaries, particularly the Cedar River. However, it is essentially a species of lakes and ponds, where it reaches its greatest abundance. Longitudinal differences in its distribution and abundance may exist, with warmouth being common in southeastern lakes and rare in southwestern lakes. The reason for this occurrence is unknown.
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.
Fish for them with a small chunk of worm near aquatic plants or rocks.
The warmouth is a sunfish species that is synonymous with lakes and ponds. It is rarely found in river lakes, overflow ponds or oxbows. The warmouth reaches abundance in a wide variety of habitats, from basic or low-gradient streams, overflow waters, marshes, swamps, and natural lakes of lowland areas, to impoundments, reservoirs and ponds in mountainous areas, assuming its microhabitat exists. The warmouth requires pooled or slow moving, clear to moderately turbid water with dense beds of aquatic vegetation and soft bottoms of silt-free, mud and organic debris. The warmouth is often found about cover, such as submerged stumps or logs.
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. The largest fish listed elsewhere was over 11 inches in length.
Recent stream sampling information is available from Iowa DNR's biological monitoring and assessment program.
Harlan, J.R., E.B. Speaker, and J. Mayhew. 1987. Iowa fish and fishing. Iowa Conservation Commission, Des Moines, Iowa. 323pp.
Loan-Wilsey, A. K., C. L. Pierce, K. L. Kane, P. D. Brown and R. L. McNeely. 2005. The Iowa Aquatic Gap Analysis Project Final Report. Iowa Cooperative Fish and Wildlife Research Unit, Iowa State University, Ames.
Photo credit: Photo courtesy of the Virtual Aquarium, The Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia.