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Testicular oocytes in smallmouth bass in northeastern Minnesota in relation to varying levels of human activity
Author(s) -
Kadlec Sarah M.,
Johnson Rodney D.,
Mount David R.,
Olker Jennifer H.,
Borkholder Brian D.,
Schoff Patrick K.
Publication year - 2017
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1002/etc.3928
Subject(s) - micropterus , bass (fish) , biology , population , population density , watershed , fishery , testicle , zoology , ecology , endocrinology , medicine , environmental health , machine learning , computer science
Testicular oocytes (TOs) have been found in black bass ( Micropterus spp.) from many locations in North America. The presence of TOs is often assumed to imply exposure to estrogenic 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 might indicate any of a number of situations: 1) unknown or unidentified EDCs or EDC sources, 2) induction of TOs by other stressors, or 3) testicular oocytes occurring spontaneously during normal development. In the present study, we analyzed TO occurrence in smallmouth bass ( Micropterus dolomieu ) from 8 populations in northeastern Minnesota watersheds with differing degrees of human development and, hence, presumed likelihood of exposure to anthropogenic chemicals. Three watersheds were categorized as moderately developed, based on the presence of municipal wastewater discharges and higher human population density (4–81 per km 2 ), and 5 watersheds were minimally developed, with very low human population density (0–1 per km 2 ) and minimal built environment. Testicular tissues from mature fish were evaluated using a semiquantitative method that estimated TO density, normalized by cross‐sectional area. Testicular oocyte prevalence and density among populations from moderately developed watersheds was higher than in populations from minimally developed watersheds. However, TO prevalence was unexpectedly high and variable (7–43%) in some populations from minimally 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. Environ Toxicol Chem 2017;36:3424–3435. © 2017 SETAC