The effect of dietary fish oil and poultry fat replacement with canola oil on swimming performance and metabolic response to hypoxia in stream type spring Chinook salmon parr

Abstract

Swimming performance, metabolic rate, and the metabolic response to hypoxia were measured in stream-type spring Chinook salmon parr ( Oncorhynchus tshawytscha) that had been reared for up to 40 weeks on diets where varying levels of refined canola oil (CO) replaced anchovy oil and poultry fat as the source of supplemental dietary lipids. Thus, CO comprised either 0% (dAPF), 25% (CO25), 49% (CO49), or 72% (CO72) of total dietary lipid. Aerobic swimming performance (repeat U crit test) was unaffected by diet in freshwater or following 24 h exposure to 75% seawater. Resting oxygen consumption (MO 2) and metabolic response to hypoxia (as indicated by the critical oxygen tension, P crit) were also unaffected by diet. Although dietary fatty acid (FA) composition clearly affected the FA composition of whole body total lipids in Chinook salmon parr, it had little effect on the FA composition and unsaturation index of whole body polar lipids. Chinook salmon parr maintained their polar lipid composition and unsaturation index, possibly through bioconversion of 18:3n−3 (linolenic acid; LNA) and 18:2n−6 (linoleic acid; LA) to their more highly unsaturated derivatives and/or by selective incorporation and retention of omega-3 FAs into the polar lipids. Because the polar lipids are largely found in membranes, this may indicate that membrane lipid composition was relatively constant across dietary groups and this, in turn, may largely explain the lack of physiological effects observed in this study. Taken together with a companion study on this same group of fish (Huang et al., 2008) where dietary treatment was not observed to adversely affect fish growth, feed intake and utilization, survival, and ionoregulatory development, there appears to be great potential for inclusion of CO in the diets of farmed pre-smolt Chinook salmon.