1. BioCentrum-DTU, Nutritional Immunology Group, Center of Biological Sequence Analysis, Technical University of Denmark, DK-2800 Lyngby, Denmark, Skretting Aquaculture Research Centre, P.O. Box 48, N-4001 Stavanger, Norway, Wageningen Institute of Animal Sciences, Aquaculture and Fisheries Group, Wageningen University, P.O. Box 338, 6700 AH Wageningen, The Netherlands, and BioProcess Engineering, Department of Chemical Engineering, Technical University of Denmark, DK-2800 Lyngby, Denmark