Sparing Fish Oil with Beef Tallow in Feeds for Rainbow Trout: Effects of Inclusion Rates and Finishing on Production Performance and Tissue Fatty Acid Composition

Sparing fish oil with alternative lipids in aquafeeds generally results in the loss of long-chain polyunsaturated fatty acids (LC-PUFAs) from farmed fish tissues; however, finishing feeds can be used to augment LC-PUFA levels prior to harvest. We reared Rainbow Trout Oncorhynchus mykiss (initial weight, 47.0 0.2g [mean +/- SE]) in a recirculation aquaculture system (190-L tanks; 16.1 +/- 0.0 degrees C water temperature) on grow-out diets containing fish oil (FO; 100% FO), beef tallow (BT; 100% BT), or blends of these lipids (50% BT, 75% BT) in combination with 4, 8, or 12 weeks of finishing with the 100% FO feed (three replicate tanks per feeding regimen; N = 3). After 31 weeks, production performance was unaffected by feeding regimen: weight gain = 1,151 +/- 30%, feed conversion ratio = 1.50 +/- 0.03, specific growth rate = 1.15 +/- 0.01% body weight/d, and feed intake = 2.19 +/- 0.02% body weight/d. Replacing fish oil with beef tallow altered tissues in favor of tallow-associated monounsaturated fatty acids at the expense of fish-oil-associated LC-PUFAs. Finishing had a corrective effect on these distortions, with longer finishing periods resulting in more comprehensive restoration. The extent of profile distortion and plasticity of the fillet, liver, intraperitoneal fat, eye, gill, and brain tissues appeared to be a function of physiological demand for certain fatty acids, lipid class composition, and tissue turnover rates; however, for all tissues, profile similarity between the control (fish fed the 100% FO feed exclusively) and experimental regimens varied with cumulative fish oil intake. Our results indicate fish oil sparing with beef tallow is an effective approach to reduce the costs of Rainbow Trout production and, if combined with finishing to augment the LC-PUFA content of the edible tissues, produce more nutritious seafood while minimizing the reliance on fish oil as a feedstuff.