Effects of Fish Oil Sparing on Fillet Fatty Acid Composition in Hybrid Striped Bass Are Influenced by Dietary Levels of Saturated and Unsaturated Fatty Acids

We assessed the growth performance and fillet fatty acid composition of hybrid Striped Bass (White Bass Morone chrysops x Striped Bass M. saxatilis; initial weight = 29.1 +/- 0.2 g [mean +/- SE]) fed diets containing only menhaden fish oil (100 FISH); fully hydrogenated saturated fatty acid (SFA)-rich soybean oil (100 SFA SOY); 75: 25, 50: 50, 25: 75, or 0: 100 blends of fish oil and standard C-18 polyunsaturated fatty acid (C-18 PUFA)-rich soybean oil (25 PUFA SOY, 50 PUFA SOY, 75 PUFA SOY, 100 PUFA SOY); or nonhydrogenated monounsaturated fatty acid (MUFA)-rich soybean oil (25 MUFA SOY, 50 MUFA SOY, 75 MUFA SOY, 100 MUFA SOY) for 8 weeks. Feed conversion ratio varied, with the 100 SFA SOY feed yielding a significantly greater value (1.3) than the rest of the feeds (0.9-1.0). Although significant treatment effects were not observed for weight gain, specific growth rate, feed intake, or organosomatic indices, some variation was observed, suggesting some minor (albeit not significant) loss of growth performance among fish fed the 100 SFA SOY and, to a lesser extent, 100 MUFA SOY feeds. Fillets of fish fed diets containing soybean-derived lipids had reduced levels of fish-oil-associated, n-3 long-chain polyunsaturated fatty acids (LC-PUFAs, i.e., 20: 5[n-3] and 22: 6[n-3]) compared with those fed the 100 FISH feed. Conversely, fillets of fish fed diets containing C-18 PUFA-rich soybean oil and nonhydrogenated MUFA-rich soybean oil had higher levels of these fatty acids (i.e., 18:2[n-6] and 18:1[n-9], respectively). Although the 100 SFA SOY diet contained substantially more SFAs (i.e., 18:0) than the other diets, these fatty acids were not proportionally elevated in the fillets. It is possible that blending SFA-rich lipids with ingredients containing some level of unsaturated fatty acids may be a means of addressing digestibility limitations while still mitigating the effects of fish oil sparing on tissue composition.