Tolerance to environmental contaminants in the mummichog, Fundulus heteroclitus

Mummichogs or killifish (Fundulus heteroclitus) are abundant estuarine fish that can tolerate, widely varying environmental conditions. They are found in some highly contaminated sites, and their development of tolerance to toxicants has been studied. Populations have developed resistance to methylmercury, kepone, dioxins, polychlorinated biphenyls, and polyaromatic hydrocarbons. This article describes what is known about their tolerance, and discusses similarities and differences among these resistant populations. In some cases tolerance is seen only in early life stages, whil e in other cases tolerance is seen in adults also. In. many of the populations, adults show signs of stress. The mechanism of embryo tolerance to meHg appears to be reduced chorionic permeability, and more rapid development through sensitive stages. One mechanism of resistance to dioxins, PCBs and PAHs is nonresponsiveness (lack of inducibility) of CYP1A. In some populations it is already elevated, while in others it is not. Another mechanism in the PAH-resistant fish is elevation of the phase II metabolizing enzyme, GST. The tolerance appears to be genetic. In populations in which it has been studied, the age structure is skewed towards younger fish, and adults appear to put more energy into reproduction as a way of maintaining the population in the stressful environment.