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Title:Patterns of intersex prevalence, vitellogenin, and reproductive condition in two commercially harvested fish along a pollution gradient in the Illinois River complex
Author(s):VanMiddlesworth, Madeleine Marie
Advisor(s):Casper, Andrew F.
Contributor(s):Fraterrigo, Jennifer M.; Levengood, Jeffrey M.
Department / Program:Natural Res & Env Sci
Discipline:Natural Res & Env Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Endocrine-disrupting chemicals (EDC)
Illinois River
Common carp
Channel catfish
Endocrine disruption
Abstract:The Illinois River in Illinois is characterized by a pollution gradient originating from highly urbanized and industrialized upstream sources that contain elevated levels of endocrine-disrupting chemicals (EDCs). Controlled exposures of fish to EDCs in laboratory have produced increased feminization of male gonadal tissue in fish (i.e. intersex condition), elevated levels of the blood lipoprotein vitellogenin (VTG), and decreased reproduction. However, assessments of the prevalence and distribution of VTG and intersex in wild fish populations are necessary and few have been performed on the Illinois River. Such field studies may provide insight into both the extent of exposure of fish to EDCs and whether there are species-specific differences in response to this exposure. Long-term data suggests that common carp populations are declining in the Illinois River while the age structure of channel catfish has shifted to primarily older fish. This study assessed gonadosomatic index (GSI), liver somatic index (LSI), intersex condition, elevated VTG levels, and fecundity indices in common carp (Cyprinus carpio) and channel catfish (Ictalurus punctatus) along a pollution gradient in the Illinois River, Illinois from the headwaters to the confluence with the Mississippi River. Common carp and channel catfish were collected along a downstream gradient of sites in the Illinois River from River Kilometer 32 to 446. Microscopic analysis of thin sections of male gonadal tissue were assessed for prevalence of intersex (oocytes in testicular tissue) in both species. In addition, I utilized a carp-specific Enzyme-Linked Immunosorbent Assay (ELISA) to contrast carp blood plasma VTG between fish caught at Upper and Lower Illinois River watershed sites. I found evidence of intersex condition in male testes from both fish species and VTG induction in male common carp, however rates of intersex were low compared to other fish species and did not vary spatially. Male carp VTG levels were not different among sites and averaged 6.7 ug/mL across all sites. This level of VTG is near or below method detection limits and low in comparison to levels in females, which had blood concentrations in the <100 ug/mL range. I also investigated whether landscape and point-source pollution factors were related to patterns of reproductive health in common carp and channel catfish. Reproductive condition was indexed using LSI, GSI, total fecundity and relative fecundity. An Akaike’s Information Criterion (AIC) modeling approach was used to identify the most influential landscape and point-source pollution-related variables. The AICc modeling produced only one candidate model in which a single health attribute, male GSI in common carp, was affected by temperature and proportion of urbanization and wetland land uses in the tributaries immediately upstream of sampling sites. These results suggest that the other select landscape attributes considered (distance of the site downstream from Chicago, adjacent land use, local point-source pollution load, and site environmental variables) had little demonstrable effect on the reproductive condition of common carp and channel catfish between locations. Reproductive metrics in fish from the heavily urbanized upper and highly agricultural lower basin sites were compared to fish collected from a disconnected, restored floodplain wetland preserve. Common carp from the Emiquon Preserve had both smaller gonads and smaller, fewer eggs at a given body length than carp from the Upper Illinois or Lower Illinois River sites. The fecundity and GSI of channel catfish did not differ between Upper River and Lower River locations. The LSI was elevated in male common carp from the Upper River and both genders of channel catfish from the Upper River locations. This study provided a baseline assessment of intersex, vitellogenin, and reproduction in two commercially important species. While many studies have examined common carp in the lab and aquaculture environments for signs of endocrine disruption, little has been documented for either wild populations of carp or channel catfish. The declining population trends for these two important Illinois River fishes and the physiological differences between species necessitates continued investigation of endocrine disruption. Contrary to the results from the examination of other select species in this river system, I found little evidence of endocrine disruption in common carp and catfish. Because this result is in strong contrast to other species in this system and elsewhere in the North America, it is essential to continue to monitor the reproductive health of these species as well as others in the Illinois River to determine the potential long-term consequences of EDCs.
Issue Date:2017-01-06
Rights Information:Copyright 2017 Madeleine VanMiddlesworth
Date Available in IDEALS:2017-08-10
Date Deposited:2017-05

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