Methylmercury Impacts to Reproduction in the Eastern Mosquitofish (Gambusia holbrooki)

Science Center Objects

USGS researchers investigate the effects of methylmercury contamination on reproduction of the Eastern mosquitofish, a common fish in South Florida.


Mosquitofish (Gambusia holbrooki) in Tanks - WARC
Mosquitofish (Gambusia holbrooki) in tanks

The Science Issue and Relevance: Many studies have documented the extent of methylmercury (MeHg) contamination in many of the environmental matrices throughout south Florida. However, relatively little work has been reported in the open literature regarding effects upon biota as a result of that contamination. Published papers pertaining to Hg impacts for the south Florida environment are either laboratory dosing studies or prospective risk assessments. All reported possible risk for piscivorous wildlife (birds, alligators, raccoons, panthers), but did not evaluate such risks for the preyed upon fish. The uncertainty of risks to fish in south Florida is significant given the elevated MeHg burdens in tissues of south Florida fish.

Methodology for Addressing the Issue: The goal of this project is to evaluate the impact of dietary MeHg exposure on fish reproduction through multiple generations. The model organism will be the eastern mosquitofish (Gambusia holbrooki), one that is very common in south Florida and is often used as a biomonitor of MeHg contamination. The mosquitofish is a fecund species with a short generation time and distinctive secondary sexual characteristics making it an ideal model organism to evaluate the impact of MeHg on fish reproduction. The exposure time frame for this project will encompass approximately three generations. The measurement endpoints that will be used to assess reproductive impacts will range from molecular (e.g., gene regulation, steroid hormones) to morphological (e.g., histology, gonopodium length) and gross reproductive (e.g., brood size, sex ratio, inter-brood interval). The selected endpoints were chosen to assess the potential for MeHg impact to fish populations. The dose levels will be selected to allow derivation of threshold effect levels that could be used by resource managers in south Florida to assess the likelihood wild fish populations are impacted based on MeHg monitoring data.

Mosquitofish (Gambusia holbrooki) in Lab - WARC
Mosquitofish (Gambusia holbrooki) in lab

Future Steps: A gene sequence library has been built for the mosquitofish (see product 1 below). That library will be used to build a microarray for evaluating gene up and down regulation as a result of MeHg exposure. Such information will enable a better understanding of the molecular effects of MeHg on fish. The laboratory studies described under project goals will commence once the library has been completed. This project will enable evaluation of risks for fish in south Florida based on the immense dataset of mercury contamination in south Florida fish.


  1. Custom Microarray construction and analysis for determining potential biomarkers of subchronic androgen exposure in the Eastern Mosquitofish (Gambusia holbrooki). 2013. BMC Genomics, V14:660.
  2. A Risk Assessment of Methylmercury to Fish in South Florida – poster presentation at Greater Everglades Ecosystem Restoration Conference, 2010.