Iowa DNR
River & Stream Biological Monitoring
Fish and Benthic Macroinvertebrate Surveys
Physical Habitat Assessments

Largemouth Bass Micropterus nigricans

Centrarchidae (Sunfishes)
Trophic Class
Top Carnivore-LMB Exclusion
Is Exotic to Iowa?
Is Lithophilous Spawner?
Is Hybrid?
State Listing Status
Not Listed
Assessment Program Statistics

This species was found at 409 bioassessment sites, 44 rapid fish bioassessment sites, 90 fisheries assessment sites, and 5 fisheries presence-only assessment sites. In total, it was collected at 526 distinct sites, or 35.8% of the 1470 total sites monitored by the bioassessment program. It is the 13th most commonly collected species.

The Largemouth Bass was collected in 729 bioassessment sampling sessions and 278 fisheries assessment sessions. It was present in 44 rapid bioassessment sessions and 5 presence-only sessions.

The biological assessment program has collected a total of 7,572 individual Largemouth Bass specimens, ranking it the #35 most collected fish.

Species Characteristics

A slender, streamlined sunfish, with a very large mouth, with the upper jaw extending far past the rear margin of the eye when the mouth is closed (except in small young). The spiny and soft portions of the dorsal fin are almost completely separated by a deep notch. The middle of the green-shaded body has a broad continuous dark stripe, but this sometimes becomes unclear in large adults and fish taken from turbid water. The belly is greenish-white or yellowish, and the eye is usually gold. The pyloric caeca, finger-like extensions at the junction of the stomach and intestine, are forked, and the tail fin in young Largemouth Bass is clearly bicolored -- not tricolored as in Spotted Bass and Smallmouth Bass. The rear part at the fin is much darker than the basal part.

Species Distribution Maps

HUC12 watersheds where this species has been found