Rates of Endocrine Disruption In Two Commercial Fishes, Common Carp and Channel Catfish, Along a Downstream Gradient In The Illinois River

Endocrine-disrupting chemicals (EDCs) can be found in high concentrations in aquatic systems, especially via point source discharges such as waste water effluent. Controlled exposures in laboratory settings suggest feminization of male fishes, such as the intersex condition in the gonads and the presence of the female-specific lipoprotein, vitellogenin, in blood circulation. Field assessments of the distribution of these characteristics in feral fish populations may provide insight into the extent of endocrine disruption within a system and which species may be more affected. The Illinois River has a notable history of pollution originating from urbanized and industrialized areas, particularly in upstream locations. This study explores patterns of intersex and elevated vitellogenin levels in mature male gonads of common carp and channel catfish collected throughout a downstream gradient of sites in the Illinois River. Standard histological techniques were utilized to assess feminization in gonadal samples. For common carp, blood plasma was also sampled for detectable levels of vitellogenin via a carp-specific Enzyme-Linked Immunosorbent Assay (ELISA) kit from specimens caught in upper and lower river sites. Evidence of feminization was observed in male testes from both fish species and preliminary results suggest a rate of intersex of 12.5% in common carp collected in the previous year in the upper river. Selected sites in the upper and lower river contained male fish with detectable levels of vitellogenin with some comparable to those of female fish that were sampled simultaneously. While many studies have examined common carp for signs of endocrine disruption, little has been documented for channel catfish populations. Both species serve economic and recreational purposes throughout the Illinois River. As declining population trends of these fishes are shown through long-term data, it may be essential to examine the reproductive health of Illinois River fishes and the future significance of feminization of male fish.