Redefining Essential Fatty Acid Requirements of Fishes in the Context of Rendered Fat-based Aquafeeds

Title: Redefining Essential Fatty Acid Requirements of Fishes in the Context of Rendered Fat-based Aquafeeds

Principal Investigator: Jesse T. Trushenski, Southern Illinois University

Keywords: Hybrid Striped Bass, Pompano, Atlantic Salmon, long-chain polyunsaturated fatty acid, LC-PUFA, Trushenski, nutrition, tallow, aquaculture, Southern Illinois University, 2012

Year: 2012

Objective:
Determine the relative requirements of long-chain polyunsaturated fatty acids EPA and DHA in beef tallow-based feeds for Atlantic salmon Salmo salar, hybrid striped bass Morone chrysops x M. saxatilis, and pompano Trachinotus carolinus.

Lay Summary/Industry Summary:
The researchers evaluated growth performance and tissue fatty acid profiles of juvenile hybrid Striped Bass Morone chrysops × M. saxatilis, Pompano Trachinotus carolinus, and Atlantic Salmon Salmo salar fed diets containing menhaden fish oil (FISH ONLY), beef tallow (BEEF ONLY), or beef tallow amended with purified sources of eicosapentaenoic acid (EPA) and/or docosahexaenoic acid (DHA) to achieve levels corresponding to 50% or 100% of those observed in the FISH ONLY feed (BEEF + 50% EPA, BEEF + 100% EPA, BEEF + 50% DHA, BEEF + 100% DHA, BEEF + 50% BOTH, BEEF + 100% BOTH). Diets were randomly assigned to replicate tanks of fish (N = 3-4, 10 fish/tank), and fish were fed assigned diets for a period of 8-10 weeks. Results suggest that beef tallow may be used as a direct replacement for menhaden fish oil in practical diets for a number of fish species, but performance may be improved by supplementation with LC-PUFA, particularly DHA. The three trials described herein have expanded our knowledge and understanding of fatty acid requirements in fish and have demonstrated that beef tallow has considerable value—perhaps even strategic value compared to traditional, plant-derived oils—as an ingredient in aquafeeds.

Scientific Abstract
Previous research suggests that saturated fatty acid (SFA)-rich lipids, including beef tallow, can make utilization of available long-chain polyunsaturated fatty acids (LC-PUFAs) more efficient in aquatic livestock. We hypothesized using beef tallow as an alternative to fish oil may effectively reduce LC-PUFA requirements of hybrid Striped Bass Morone chrysops × M. saxatilis, Pompano Trachinotus carolinus, and Atlantic Salmon Salmo salar and allow for greater fish oil sparing. Accordingly, we evaluated growth performance and tissue fatty acid profiles of juvenile fish fed diets containing menhaden fish oil (FISH ONLY), beef tallow (BEEF ONLY), or beef tallow amended with purified sources of eicosapentaenoic acid (EPA) and/or docosahexaenoic acid (DHA) to achieve levels corresponding to 50% or 100% of those observed in the FISH ONLY feed (BEEF + 50% EPA, BEEF + 100% EPA, BEEF + 50% DHA, BEEF + 100% DHA, BEEF + 50% BOTH, BEEF + 100% BOTH). Diets were randomly assigned to replicate tanks of fish (N = 3-4, 10 fish/tank), and fish were fed assigned diets for a period of 8-10 weeks. With respect to Hybrid Striped bass, survival (98―100%) was equivalent among treatments, but weight gain (117―180%), specific growth rate (1.1―1.5% body weight/d), feed intake (1.4―1.8% body weight/d), and feed conversion ratio (FCR; 1.1―1.4, dry matter basis) varied. Except for FCR, no differences were observed between the FISH and BEEF treatments, but performance was generally superior among fish fed the BEEF + 100% DHA, BEEF + 50% BOTH, and BEEF + 100% BOTH diets. Regarding Pompano, production performance was largely unaffected by dietary lipid source and fatty acid composition. Weight gain (183-223%), specific growth rate (1.85-2.09% body weight/d), feed intake (3.37-3.71% body weight/d), and FCR (1.60-1.85, dry matter basis) varied slightly among dietary treatments, but not significantly. Fish fed the negative control feed BEEF ONLY exhibited equivalent performance as those fed the positive control feed FISH ONLY. Supplementing beef tallow-based diets with DHA alone had a greater effect on growth than supplementing in combination with EPA or with EPA alone. With respect to Atlantic salmon, (N = 3, 30 fish/tank, 14-week feeding period) survival (99―100%) was also equivalent among treatments. Weight gain was consistent, apart from BEEF ONLY out-performing BEEF + 50% EPA 50% (~250%), though no difference in specific growth rate (~1.3% body weight/d) was observed. Feed intake was highest in BEEF ONLY and lowest in BEEF + 100% BOTH (3.0―2.2% body weight/d). Feed conversion ratio was lowest among fish fed the FISH ONLY feed, but equivalent in all other treatments (0.9―1.0) varied. Organosomatic indices did not vary. Tissue fatty acid composition was significantly distorted in favor of SFAs and monounsaturated fatty acids among fish fed the beef tallow-based feeds; however, changes in fatty acid profiles were generally less overt than those typically induced by C18 polyunsaturated fatty acid-rich plant oils. Results suggest that beef tallow may be used as a direct replacement for menhaden fish oil in practical diets for a number of fish species, but performance may be improved by supplementation with LC-PUFA, particularly DHA.