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Testicular oocytes in smallmouth bass in northeastern Minnesota in relation to varying levels of human activity
Citation:
Kadlec, S., R. Johnson, Dave Mount, J. Olker, B. Borkholder, AND P. Schoff. Testicular oocytes in smallmouth bass in northeastern Minnesota in relation to varying levels of human activity. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 36(12):3424-3435, (2017).
Impact/Purpose:
Testicular oocytes (egg cells occurring in the testes of male fish) have been reported to occur in wild smallmouth bass from a number of locations across the US, and occurrence of testicular oocytes is often taken to imply the presence of exposure to estrogenic chemicals (chemicals that mimic the action of natural estrogens). However, relatively little is known about the occurrence of testicular oocytes across lakes with different degrees of human influence, and particularly in remote lakes where there should be little or no estrogenic exposure. This manuscript explores the occurrence of testicular oocytes (eggs cells occurring in the testes of male fish) in several watersheds in northeastern Minnesota, representing a range of human population and development. Testicular oocytes were significantly more common in the three watersheds with higher levels of development, but were also found in all of the more remote lakes, sometimes with frequencies close to those in the more highly developed watersheds. Correlations of testicular oocyte occurrence with human development were relatively weak, and were similar in strength to those with fish size and other, unrelated factors. This suggests that testicular oocytes in smallmouth bass likely arise from multiple causes, and probably should not be taken as unique evidence of exposure to estrogenic chemicals.
Description:
Testicular oocytes (TOs) have been found in black basses (Micropterus spp.) from many locations in North America. The presence of TOs is often assumed to imply exposure to endocrine disrupting compounds (EDCs), however, a definitive causal relationship has yet to be established, and TO prevalence is not consistently low in fish from areas lacking evident EDC sources. This could suggest unknown or unidentified EDC sources, or that TOs can be stimulated by other stressors, or that they arise spontaneously during normal development. In the present study we analyzed TO occurrence in smallmouth bass (M. dolomieu) from eight populations in Northeastern Minnesota watersheds with differing degrees of human development and hence, likelihood of EDC exposure. Three watersheds were categorized as more developed, based on the presence of municipal wastewater discharges and higher human population density, and five watersheds were less developed, with very low human population density and minimal built environment. Testicular tissues from mature fish were evaluated using a semi-quantitative method that estimated TO density, normalized by cross-sectional area. TO prevalence and density among populations from more developed watersheds was higher than in populations from less developed watersheds. However, TO prevalence was unexpectedly high and variable (7-43%) in some populations from less developed watersheds, and only weak evidence was found for a relationship between TO density and watershed development, suggesting alternative or more complex explanations for TO presence in smallmouth bass from this region.
