Effect of dietary canola oil level on the growth performance and fatty acid composition of juvenile red sea bream, Pagrus major

This study was undertaken to evaluate the suitability of using refined canola oil as a source of supplemental dietary lipid for juvenile red sea bream (Pagrus major). Triplicate groups of 25 red sea bream fingerlings held under identical culture conditions (25 °C, aerated, re-circulated artificial seawater, 30 g/L; 12-h light/12-h dark photoperiod) were fed three times daily to satiation one of four diets with equivalent protein (approximately 46%), energy (approximately 21.9 MJ/kg) and lipid (approximately 15%) content on a dry weight basis for 12 weeks. The diets were identical in composition except refined canola oil (CO) replaced either 0%, 33%, 67%, or 100% of the supplemental dietary lipid content with the remainder originating from pollock liver oil (FO). Thus CO comprised either 0% (diet FO), 25% (CO25), 48% (CO48), or 70% (CO70) of total dietary lipid content. Fish weight gain, specific growth rate, feed intake, feed efficiency, protein and gross energy utilization, and percent survival were not affected by diet treatment. Except for percent moisture which was depressed in CO48 and CO70-fed fish, concentrations of terminal whole body proximate constituents were similarly uninfluenced by diet treatment. Dietary lipid compositions reflected the proportions of CO and FO in supplemental lipid and their respective fatty acid compositions. Whole body fatty acid compositions mirrored those of diet treatments. However, liver polar lipids of the fish suggested, some essential fatty acids such as eicosapentaenoic acid, docosahexaenoic acid and arachidonic acid were preferentially incorporated and regulated, which resulted in a relatively lower degree of difference between diet treatments compared to what was found in whole body lipid. Our findings suggest that refined canola oil is a suitable dietary lipid source for juvenile red sea bream under our test conditions. However, chronic assessments of CO as a supplemental dietary lipid source for red sea bream are warranted to ensure that similar results are obtained without adverse effects on fish health.