Eastern mosquitofish as a bioindicator of pulp and paper mill effluents.

摘要

A variety of sublethal physiological effects have been reported for fish exposed to pulp and paper mill effluents. As mill processing technologies improve, mounting evidence demonstrates fewer effects potentially linked to reduction in wood extractives. Repercussions of sublethal effects at higher levels of biological organization are important questions beginning to be explored. The goal of my study was to evaluate whether sublethal effects in mosquitofish can be used reliably to indicate adverse impact of pulp and paper mill effluents. Biomarkers of anal fin morphology and whole body sex steroids were validated, then studied extensively in wild-caught mosquitofish from Florida effluent-receiving streams that varied markedly in effluent composition. These biomarkers were also examined under short-term controlled whole effluent exposures (caged in field and in tanks at 0, 10, 20, 40, and 80% dilutions); and in relation to fry production and preliminary population surveys. Extent of female anal fin masculinization, or development of male-like secondary sex characteristics, was associated with increasing concentrations of wood extractives in water samples from field sites. Implementation of EPA's Cluster Rule at one mill was followed by a significant reduction, but not elimination, of this response. However, masculinization could not be reproduced under controlled exposure, likely due to insufficient exposure duration. Alterations in sex steroids were manifested in both sexes for wild-caught and experimentally-exposed fish: males exhibited feminized hormonal profiles will females displayed masculinized profiles. Differential responses among cage-exposed and tank-exposed fish indicated additional environmental factors (such as bacterial communities hypothesized to degrade effluent components into androgenic compounds) were influential in producing responses. However, large natural variation at unexposed sites and indication of seasonality precluded definitive interpretation. The lack of association between these biomarkers demonstrated whole body sex steroids cannot be used to predict morphological masculinization; but they can be compared as biomarkers of recent versus past exposure. Finally, reproductive success studies implied mosquitofish may adapt different reproductive strategies in effluent-receiving streams. Since neither biomarker could be linked to differences in fry production or population structure, at this point mosquitofish may not be a suitable bioindicator of adverse effects due to pulp and paper mill effluents.