1. The Fish Physiology Research Group, Department of Biology and Biochemistry, Brunel University, Uxbridge, Middlesex UB8 3PH, U.K., Environment Agency, National Fisheries Laboratory, Bromholme Lane, Brampton, Cambs PE18 8NE, U.K, and Environment Agency, National Centre for Ecotoxicology and Hazardous Substances, Hawberry Park, Wallingford, Oxon OX10 8BD, U.K.