More Judicious Use of Fish Oil in Cobia Feeds: II. Effects of Graded Fish Oil Sparing and Finishing

Abstract

AbstractReplacement of long‐chain (LC) polyunsaturated fatty acid (PUFA)‐rich fish oil with alternative lipids in aquafeeds typically reduces the LC‐PUFA content and associated nutritional value of farmed fish even if production performance is unaffected. Finishing can be used to augment tissue LC‐PUFA levels prior to harvest; however, the effectiveness of this strategy for use with the Cobia Rachycentron canadum is relatively unknown. For 8 weeks, Cobias (initial weight [mean ± SE] = 59.8 ± 0.2 g) were fed diets in which the supplemental lipid consisted of 100% fish oil; 100% beef tallow; a blend of 33% beef tallow and 67% fish oil; or a blend of 67% beef tallow and 33% fish oil. After the 8‐week grow‐out period, all treatment groups received the 100% fish oil feed for 6 weeks to simulate finishing. Differences in production performance were observed, but growth and growth efficiency were not reduced by inclusion of beef tallow in the grow‐out feeds. Prior to the finishing period, fatty acid profiles of fillet, liver, eye, and brain tissues varied considerably among treatments. As finishing progressed, tissue profiles converged on the profiles of fish that were fed the 100% fish oil diet exclusively. Specifically, saturated fatty acids (SFAs) and monounsaturated fatty acids (MUFAs) declined, whereas LC‐PUFA levels varied relatively little during the trial. Results indicate that SFA‐ and MUFA‐rich alternative lipids like beef tallow minimize LC‐PUFA loss during grow‐out and that finishing feeds can be used to modify Cobia tissue profiles prior to harvest.