DHA is essential, EPA appears largely expendable, in meeting the n − 3 long-chain polyunsaturated fatty acid requirements of juvenile cobia Rachycentron canadum

Cobia may require both eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids to meet dietary n − 3 long-chain polyunsaturated fatty acid (LC-PUFA) demand. Growth performance is reduced when LC-PUFA-rich fish oil is replaced with soybean oil, a LC-PUFA deficient lipid, in cobia diets, but individual requirements for EPA and DHA have not been quantitatively determined. We assessed the growth performance and tissue fatty acid composition of juvenile cobia fed a fish oil-based positive control diet (FISH), a soy oil-based negative control diet (SOY), or experimental diets based on soy oil supplemented with EPA, DHA, or both at 50% or 100% of the concentrations typically observed in fish oil: (SOY + 50% EPA, SOY + 100% EPA, SOY + 50% DHA, SOY + 100% DHA, SOY + 50% BOTH, SOY + 100% BOTH). Growth performance of fish fed the SOY was impaired relative to those fed the FISH diet. Supplementing the soybean oil-based diet with DHA, alone or in combination with EPA, restored performance. EPA supplementation had no effect on growth performance. Fatty acid composition of cobia fillet, liver, brain, and eye tissues was significantly affected by diet, but tissue profile change among fish fed any of the soy oil-based diets was less overt in the brain compared to the periphery. Diets supplemented with DHA and/or EPA resulted in increased tissue levels of these fatty acids, however, the maximal levels were observed in the FISH treatment. Our data suggest the dietary n − 3 LC-PUFA requirement of juvenile cobia can be largely satisfied by DHA, and that EPA, if required, is required only in trace amounts. Soybean oil supplemented with DHA is an effective alternative to fish oil in juvenile cobia diets.