1. Laboratory of Food Technology, Faculty of Pharmacy, University of Basque Country, Marques de Urquijo s/n, 01006 Vitoria, Spain, Fish Nutrition Laboratory, Unité mixte INRA - IFREMER, B.P. 3, 64310 Saint-Pée-sur-Nivelle, France, French Veterinary Medicine Agency, CNEVA, B.P. 203, 35302 Fougères, cedex, France, and Laboratory of Biochemistry, Faculty of Science, University of Basque Country, B.P. 644, 48080 Bilbao, Spain