Effects of reduced feed ration levels on fat content and fatty acid composition in white and red muscle from rainbow trout

Abstract

The effects of different ration levels (RL) on lipid content and composition in red and white muscle of rainbow trout ( Salmo gairdneri Rich.) were investigated in a study lasting from start-feeding throughout life. Three experimental ration levels, adequate feeding, moderate restriction and strong restriction, were defined according to expected growth. Groups of trout were maintained at constant experimental ration levels, or subjected to changed levels. In this paper results from the first year of the ongoing experiment are presented. Total fat content was low in white and high in red muscle, with only minor differences between the groups. The fat content of the dorsal fat depot, however, was very low when RL was low but rose with increasing rations. The amount of saturated fatty acids was about the same in white and red muscle. Monounsaturated fatty acids were higher, whereas polyunsaturated fatty acids were lower, in red than in white muscle. Changing RL caused changes in mono- and polyunsaturated fatty acids in white as well as in red muscle, especially in the groups where RL was reduced from high to low and increased from low to high. This was particularly evident for the monounsaturated fatty acids 16:1, 18:1, 20:1 and 22:1 and the polyunsaturated acids 20:5 and 22:6. The fatty acid composition in muscle deviated from that of the feed. Thus, the content of 16:0, 18:1 and 22:6 was high, whereas 20:1, 22:1 and 20:5 were low in muscle compared to feed.