La Crosse Fish and Wildlife Conservation Office
Biologist Pilot Study Reveals Intersex Condition in Largemouth Bass from Lower Des Plaines River, Illinois
BY MARK FRITTS, LA CROSSE FWCO
tissue of a largemouth bass collected from the Dresden Reach of the Illinois
River Waterway, Illinois, U.S.A. in 2014. Credit: Mark Fritts, USFWS
intersex analysis during 2014 in the Dresden
Reach of the upper Illinois River Waterway,
Illinois, U.S.A. Credit: Map courtesy of US
In recent nationwide studies, one of the most commonly used biomarkers to assess the effects of EDCs on fishes is the presence of eggs in male fish testes (i.e., intersex condition). Previous studies have indicated that Chicago-area streams have relatively high concentrations of EDCs known to induce intersex condition. Many of these streams also feed eventually into the lower Des Plaines River and the Illinois River Waterway. Thus, during spring 2014, Illinois Natural History Survey Fish Biologist Mark Fritts, who is now a biologist with the La Crosse FWCO, headed an EDC pilot study in the Dresden Island reach of the Illinois Waterway near Joliet, Illinois. The objective of the study was to survey the severity of intersex in male largemouth bass in an area directly affected by surface runoff and wastewater effluents from the Chicago Metropolitan Area. Previous studies have shown that largemouth bass are known to be very vulnerable to EDC exposure. Largemouth bass were collected during April and May, when the probability of catching pre-spawn males – and therefore detecting intersex condition – would be greatest. Testicular tissue samples were processed by the Veterinary Diagnostic Lab at the University of Illinois-Urbana Champaign.
Intersex condition was detected in 21 of 51 (41%) male largemouth bass collected during 2014. Interestingly, intersex males did not differ from normal males in length, weight, age, gonadal/somatic and hepatic/somatic indices of condition. Although no discernable differences in these metrics were observed between intersex and normal males, there could still be behavioral or reproductive differences that went undetected in this pilot study. A peer-reviewed manuscript of these results has been accepted, and is available in the July 2016 edition of American Midland Naturalist. As a follow-up to this 2014 pilot study, current INHS biologists have expanded the spatial and taxonomic scope of the study during 2015-16 to include collections of bluegill and black crappie at riverine sampling locations extending over 100 km downstream of the initial collection sites sampled in 2014.