Adaptations of wild populations of the estuarine fish Fundulus heteroclitus to persistent environmental contaminants

Many aquatic species, including the estuarine fish Fundulus heteroclitus (m ummichogs), adapt to local environmental conditions. We conducted studies t o evaluate whether highly exposed populations of mummichogs adapt to toxic environmental contaminants. These fish populations are indigenous to an urb an estuary contaminated with persistent and bioaccumulative contaminants (d ioxin-like compounds, or DLCs) that are particularly toxic to the early dev elopment of fish. We conducted laboratory challenge experiments to compare mummichog embryos and larvae from reference sites and this highly contamina ted site [New Bedford Harbor (NBH), Massachusetts, USA] for their sensitivi ty to DLCs. While there was variation in DLC-responsiveness within each gro up, fish from NBH were profoundly less sensitive to DLCs than reference fis h. Specifically, concentrations of DLCs similar to those measured in NBH-co llected mummichog eggs were lethal to reference embryos. Further, DLC-respo nsiveness was inherited and independent of maternal contaminant contributio ns. These findings are consistent with the conclusion that DLC contaminatio n in NBH has contributed to the selection of fish that are resistant to the short-term toxic effects of these environmental-contaminant exposures. Thi s adaptation may be a critical mechanism by which fish populations persist in this highly contaminated site. Further evaluation of this ecosystem may provide important information concerning the direct and indirect consequenc es of this "unnatural" selection.