Reevaluating polyunsaturated fatty acid essentiality in hybrid Striped Bass

Understanding fatty acid requirements in multiple taxa is necessary to determine the degree to which dietary fish oil can be reduced or replaced with less costly, more abundant lipid sources. The polyunsaturated fatty acid (PUFA) requirements of hybrid Striped Bass (White Bass Morone chrysops x Striped Bass M. saxatilis) are currently reported as 0.5-1.0% eicosapentaenoic acid (20:5n-3) and/or docosahexaenoic acid (22:6n-3). This requirement does not account for n-3 PUFA essentiality on an individual fatty acid basis and does not address possible requirements for n-6 PUFAs (i.e., linoleic acid [18:2n-6] or arachidonic acid [20:4n-6]). Accordingly, hybrid Striped Bass were fed diets containing selected individual n-3 and n-6 C-18 PUFAs, n-3 and n-6 long-chain (LC) PUFAs, or combinations thereof to determine the essentiality or expendability of these nutrients. These experimental feeds were compared to feeds containing only saturated fatty acids (negative control) or menhaden fish oil (positive control). Growth performance and ratios of 22:5n-6 : 22:6n-3 observed in tissue fatty acid profiles suggested that dietary provision of 22:6n-3 was adequate to satisfy physiological demand for LC-PUFAs. However, reductions in feed conversion ratio and numeric improvements in growth suggest that dietary provision of 20:4n-6 is also important. Results of this study indicate that provision of C-18 PUFAs alone is insufficient to avoid essential fatty acid deficiency and to support optimal growth of this fish. To ensure that essential fatty acid requirements are met and performance is optimized, diets for hybrid Striped Bass should be formulated to contain 22:6n-3 and 20:4n-6, if not a full complement of n-3 and n-6 LC-PUFAs.