Environmental levels of heavy metals like mercury have increased significantly over the last 100 years in response to anthropogenic activities. More recently the increase in acid precipitation may make the situation worse in that it appears to increase the production of methyl mercury (MeHg) in the surface waters and benthic regions. Concentrations of mercury in surface waters are normally relatively low in the ng/L range, yet levels of mercury in fish tissue in the mg/L range are not uncommon. There have been several well-publicized accounts of acute mercury poisoning from consuming highly contaminated fish. Less is known about the health risks associated with consumption of fish with low levels of mercury contamination. Human embryos are especially sensitive to MeHg's teratogenic effects. For example, psychomotor retardation is a common outcome of fetal MeHg exposure. Such neural effects may be the result of abnormal migration of neurons during development. A number of different species have been utilized to investigate the effects of mercury on teleost development. Coho salmon, like all teleostean embryos possess mitotic cells that provide a useful model for the study of MeHg teratogenesis. Due to their large size, coho salmon embryos are easily observed and maintained in the laboratory.more » In addition large numbers of eggs are available from one female thus minimizing effects of variability among individuals. The objective of the present study is to characterize the toxic levels of MeHg and study their uptake. In addition some of the teratogenic effects of MeHg on coho salmon embryos will be described. 16 refs., 3 figs., 1 tab.« less