1. Division of Zoology, Department of Biology, University of Oslo, PO Box 1050 Blindern, N–0316 Oslo, Norway,,
2. Department of Morphology, Genetics and Aquatic Sciences, Norwegian College of Veterinary Medicine, PO Box 8146 Dep., N–0033 Oslo, Norway,,
3. Division of General Genetics, Department of Biology, University of Oslo, PO Box 1031 Blindern, N–0315 Oslo, Norway