Non-Essential Heavy Metals as Endocrine Disruptors: Evaluating Impact on Reproduction in Teleosts

The concentrations of ubiquitous heavy metals such as mercury (Hg), lead (Pb), chromium (Cr) and cadmium (Cd) can be enhanced in freshwater aquatic systems through anthropogenic activities. The present review collates the current information concerning their probable role as endocrine disruptors affecting fish reproduction. During the last two decades, several studies have implicated the toxic effects of sublethal metal exposure on different reproductive parameters in fish. This report summarizes results from both laboratory and field studies favouring the hypothesis that metals can disrupt fish reproduction, and analyzes the possible mechanisms of metal-induced reproductive impairments. The endocrine disrupting effects have been discussed separately in male and female fish for each metal. The four metals were found to elicit disrupting activity at the level of brain neurotransmission, hypothalamo-hypophyseal hormone axis and/or gonad structure and function. The metals modulated expression of different reproduction related genes possibly through altered transcription factor activity. Some critical issues related to the area such as effects of low level environmentally relevant metal exposure, presence of confounding factors, and assessment of possible additive, synergistic or antagonistic effects of different metals are identified as future research topics.