1. Laboratory for Endocrinology, Department of Biology, Faculty of Science, University of Utrecht, Padualaan 8, NL-3584 CH Utrecht, The Netherlands, Department of Molecular Biology, University of Bergen, HiB, Thormoehlensgt. 55, N-5020 Bergen, Norway, and Environmental and Molecular Fish Biology Group, School of Biosciences, Hatherly Laboratories, University of Exeter, Prince of Wales Road, Exeter, Devon, EX4 4PS, UK