Female reproductive impacts of dietary methylmercury in yellow perch (Perca flavescens) and zebrafish (Danio rerio)

Authors: DEBOFSKY, ABIGAIL - University Of Wisconsin; KLINGER, REBEKAH - University Of Wisconsin; MORA, FRANCISCO - University Of Wisconsin; WALTZ, MARCUS - University Of Wisconsin; Shepherd, Brian; LARSON, JEREMY - University Of Wisconsin; ANDERSON, DAVID - University Of Wisconsin; YANG, LUOBIN - Idaho State University; GOETZ, FREDERICK - National Oceanic & Atmospheric Administration (NOAA); BASU, NILADRI - McGill University - Canada; HEAD, JESSICA - McGill University - Canada; TONELLATO, PETER - University Of Wisconsin; MURPHY, CHERYL - Michigan State University; CARVAN, MICHAEL - University Of Wisconsin

Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2017
Publication Date: 12/6/2017
Citation: Debofsky, A.R., Klinger, R., Mora, F.X., Waltz, M., Shepherd, B.S., Larson, J., Anderson, D., Yang, L., Goetz, F., Basu, N., Head, J., Tonellato, P., Murphy, C., Carvan, M.J. 2017. Female reproductive impacts of dietary methylmercury in yellow perch (Perca flavescens) and zebrafish (Danio rerio). Chemosphere. 195:301-311. https://doi.org/10.1016/j.chemosphere.2017.12.029.
DOI: https://doi.org/10.1016/j.chemosphere.2017.12.029

Interpretive Summary: While farmed fish have significantly lower mercury levels than wild-caught fish, suggesting that farmed fish are safer (in this regard) for human consumption, very little effort has been focused on how mercury impacts the physiology of domesticated fish species. This is particularly important for initiation of breeding and genetic improvement programs, such as on-going work in yellow perch. In this study, we sought to evaluate the effects of environmentally relevant dietary methyl-mercury (MeHg) exposures on adult female yellow perch (Perca flavescens) and zebrafish (Danio rerio) reproduction. Yellow perch were used in the study for their socioeconomic importance within the Great Lakes basin. While analyses of ovarian gene expression in zebrafish exposed over their entire life-cycle showed changes in several genes involved in reproductive processes, there were no significant changes observed with ovarian staging, fecundity (egg production), or embryo mortality. By contrast, measures of ovarian gene expression, ovarian somatic index, circulating estradiol, and ovarian staging were not altered by MeHg exposure in yellow perch. These results suggest that environmentally relevant MeHg exposures, over a short-time period, do not reduce the spawning ability of yellow perch during a single season. However, whole life-cycle exposures, similarly to that conducted in zebrafish, should be conducted in yellow perch to ensure that environmentally-relevant doses do not affect life-time reproductive capacity in this species.

Technical Abstract: The purpose of this study was to evaluate the effects of environmentally relevant dietary MeHg exposures on adult female yellow perch (Perca flavescens) and zebrafish (Danio rerio)reproduction. Yellow perch were used in the study for their socioeconomic and ecological importance within the Great Lakes basin, and the use of zebrafish allowed for a detailed analysis of the molecular effects of MeHg following a whole life-cycle exposure. Chronic dietary exposure of zebrafish to MeHg mimics realistic wildlife exposure scenarios, and the twenty-week adult yellow perch exposure (where whole life-cycle exposures are difficult) captures early seasonal ovarian development. In zebrafish, several genes involved in reproductive processes were shown to be dysregulated by RNAsequencing and quantitative real-time polymerase chain reaction (QPCR), but no significant phenotypic changes were observed regarding ovarian staging, fecundity, or embryo mortality. Yellow perch were exposed to dietary MeHg for 12, 16, or 20 weeks. In this species, a set of eight genes were assessed by QPCR in the pituitary, liver, and ovary and no exposure-related changes were observed. The lack of genomic resources in yellow perch hinders the characterization of subtle molecular impacts. The ovarian somatic index, circulating estradiol and testosterone, and ovarian staging were not significantly altered by MeHg exposure in yellow perch. These results suggest that environmentally relevant MeHg exposures do not drastically reduce the spawning capacity of these fish, but to capture realistic exposure scenarios, whole life-cycle yellow perch exposures are needed.