Warmouth

Characteristics

A thick-bodied, stout-looking 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 noticeable on the soft parts of the dorsal and anal fin. It can easily be distinguished from other sunfish by the patch of small teeth on the tongue. Anglers often confuse this fish 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, has 10 spines.

Distribution

Found throughout the Mississippi River; rarely taken in the lower reaches of its tributaries, mainly the Cedar River. Most abundant in lakes and ponds. Longitudinal differences in its distribution and abundance may exist, with Warmouth common in southeastern lakes and rare in southwestern lakes. The reason for this is unknown.

Foods

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

State Record

1.13 lbs 10.75 in. - farm pond, Taylor County, May 12, 2018 - Celsey Rynearson, Milo, Iowa

Expert Tip

Use a small chunk of worm near aquatic plants or rocks.

Details

Warmouth are a sunfish species that is synonymous with lakes and ponds. It is rarely found in river lakes, overflow ponds or oxbows. It reaches abundance in a 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, if its microhabitat exists. Warmouth need 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. It is often found around cover, such as submerged stumps or logs.

Warmouth, like all members of this family, build a nest to deposit eggs in. Nest building starts 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 built in 1 1/2 to 4 feet of water. The male builds and closely guards the nest until the fry leave. 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 long by autumn and maximum size of about 7- to 8-inches by the fifth year of life. The largest fish listed elsewhere was over 11-inches long.

Recent stream sampling information is available from Iowa DNR's biological monitoring and assessment program.

Sources:

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.