Effects of dietary canola oil level on growth performance, fatty acid composition and ionoregulatory development of spring chinook salmon parr, Oncorhynchus tshawytscha

Abstract

This study assessed the potential of refined canola oil (CO) as a source of supplemental dietary lipid for pre-smolt spring chinook salmon (Oncorhynchus tshawytscha) over a period of 30 weeks. Triplicate groups of 320 fry (∼0.80 g), reared in flow-through well water (8–11.5 °C), were fed one of four steam-pelleted dry diets with equivalent gross energy (24.3 MJ/kg), protein (∼51.3%) and lipid (∼21.6%) content on a dry-weight basis. CO furnished either 0%, 33%, 67%, or 100% of the supplemental dietary lipid, with the remainder from a commercial blend of 1:1 anchovy oil and poultry fat (APF). Thus, CO comprised either 0% (dAPF), 25% (CO25), 49% (CO49), or 72% (CO72) of total dietary lipid content. Overall fish growth rate, feed intake, feed efficiency, protein utilization, percent survival, and terminal whole body proximate constituents were unaffected by diet treatment. Dietary lipid compositions reflected the ratios of CO and APF in the supplemental lipid and their respective fatty acid compositions. Whole body fatty acid compositions mirrored those of diet treatments. However, some essential fatty acids, namely, arachidonic acid (20:4n-6; AA), and docosahexaenoic acid (22:6n-3; DHA) were conserved in fish regardless of dietary CO level. Direct relationships were found between dietary and whole body concentrations of: 18:2n-6 (R2=0.94; slope=0.72), 18:3n-3 (R2=0.99; slope=0.58), 20:4n-6 (R2=0.84; slope=0.42), 20:5n-3 (R2=0.99; slope=0.43) and 22:6n-3 (R2=0.82; slope=1.25). High dietary levels of 18:3n-3, 18:2n-6, and 20:5n-3 may have been utilized for energy or converted to more unsaturated derivatives. Overall development of ionoregulatory ability, as assessed by 24-h seawater challenge tests, was unaffected by diet. However, whole body chloride content was generally inversely related to dietary CO level during early development. Our findings suggest that there is excellent potential for long-term replacement of fish oil with canola oil in the diet of pre-smolt spring chinook salmon, provided that some marine oil is present to ensure that the essential fatty acid needs of the fish are met.