1. Brixham Environmental Laboratory, AstraZeneca UK Limited, Freshwater Quarry, Brixham, Devon, TQ5 8BA, U.K., School of Biological Sciences, The Hatherley Laboratories, University of Exeter, The Prince of Wales Road, Exeter, Devon, EX4 4PS, U.K., Department of Biology and Chemistry, University of Bremen, Germany, and Fish Physiology Research Group, Department of Biological Sciences, Brunel University, Uxbridge, Middlesex, UB8 3PH, U.K.