Basin-scale patterns of common carp physiological condition associated with EDC exposure in a large Anthropocene river

Common carp (Cyprinus carpio) is a commercially and recreationally important species that has declined by > 80% across the Illinois River basin since the 1960s, suggesting impairment of population-level reproduction. Numerous controlled experiments have shown common carp reproductive physiology is susceptible to endocrine-disrupting chemical (EDC) exposure at levels commonly associated with the urban and agricultural reaches of this large river. The aim of our study was to investigate spatial patterns of potential physiological and reproductive impairment in common carp related to basin-scale differences in land use. There were complex sex-specific differences in the spatial patterns of several biomarkers we examined from common carp in the Illinois River, suggesting common carp may be exhibiting physiological effects related to EDCs and other contaminants. Biomarkers in female common carp showed little spatial variation along the Illinois River, whereas multiple biomarkers in male common carp indicated a spatially variable response. However, the low prevalence of intersex condition in male common carp contrasts with centrarchid species from the same system, perhaps because of differences in trophic position, habitat use, or physiology. This same low prevalence of intersex may preclude the utility of blood plasma vitellogenin as a nonlethal indicator of intersex in male common carp. Ultimately, despite the evidence of intersex in largemouth bass and black crappie from the Illinois River, we conclude that it is unlikely that EDC exposure leading to intersex condition is contributing to the declining common carp population in this river.