Title: Lysine optimization of a commercial fishmeal-free diet for hybrid striped bass (Morone chrysops x M. saxatilis) Authors
Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 13, 2013
Publication Date: March 5, 2013
Citation: Rawles, S.D., Fuller, S.A., Beck, B.H., Gaylord, T.G., Barrows, F., McEntire, M.E. 2013. Lysine optimization of a commercial fishmeal-free diet for hybrid striped bass (Morone chrysops x M. saxatilis). Aquaculture. 396-399:89-101. Interpretive Summary: When fishmeal in fish feed is replaced with different proteins, fish performance is often poor due to imbalances in essential nutrients in the resulting feed. This growth trial with hybrid striped bass was undertaken to test the hypothesis that the essential amino acid levels found in the muscle of hybrid striped bass accurately predict the levels that should be added to the diet when fishmeal is completely replaced by another protein in the diet. The basic test diet for this trial was composed of soybean (45%), corn gluten (10%), and poultry by-product (13%) meal as the protein sources. This high level of soybean meal in fish diets has caused intestinal allergies and poor growth in fish other than hybrid striped bass, so we were interested to examine the intestines of the fish fed our test diets. Two of the most deficient essential amino acids (Methionine and Threonine) were added to the base diet at the same levels found in the muscle of hybrid striped bass. Finally, seven different levels of another essential amino acid, Lysine, were added to the base diet in order to determine the optimum level of Lysine for maximum fish growth and nutrient retention. In addition, the diet formulas used our most recent data on the availability of essential nutrients in the different diet ingredients for hybrid striped bass. The test diets were extruded to achieve the same physical and chemical characteristics as a commercial-grade feed and then fed to hybrid striped bass for 12 weeks. In conclusion, hybrid striped bass muscle appears to be a reasonable pattern of essential amino acid ratios and levels to target for fishmeal-free diets for this fish. Given our current database of feed ingredient profiles and nutrient availabilities, this method of diet formulation was a sensitive indicator of the order and level of nutrient limitation, and will become more sensitive as we obtain more accurate long-run averages of nutrient availabilities in our growing database of feedstuffs. Finally, hybrid striped bass seem much less sensitive to soybean intestinal allergies than other commercial fish species.
Technical Abstract: Substitution of fishmeal with alternate proteins in aquafeeds often results in dietary imbalances of firstlimiting essential amino acids (EAA) and poorer fish performance. This growth trial was undertaken to test the hypothesis that ideal protein theory accurately predicts first-limiting amino acids and optimum lysine level for a fishmeal-free, commercial-grade diet formulated for hybrid striped bass (HSB). The ideal model for formulation was the amino acid pattern of hybrid striped bass muscle. A negative control diet based on soybean (45%), corn gluten (10%), and poultry by-product (13%) meals was formulated on an ideal basis to contain 18% lipid, 40% crude protein (CP), 36% digestible protein (DP) and 1.8% Lys from intact sources. Met and Thr were then added at levels equivalent to 40% protein from HSB muscle to form a basal diet that was fortified with seven levels of Lys (2.2 to 6.4 g /g diet) that bracketed the predicted ideal Lys requirement (3.5g/g diet) for this formulation. Diets were extruded to achieve similar characteristics as a commercial-grade feed and fed to juvenile fish (118 g BW) for 84 d. Response data were subjected to polynomial and exponential regression and the best model per response selected based on the lowest error (MSE) and p-values and the highest adjusted R2. Selected models were used to derive dietary Lys levels required to reach 95% (R95) or 99% (R99) of the minimum or maximum response. Final fish weights (328–369g) increased linearly with increasing dietary Lys. Weight gain, average daily feed intake (1.42-1.7%), and feed efficiencies at 4-, 8-, and 12-week intervals were modeled by cubic functions That yielded consistent R95 and R99 levels of about 2.4 and 4.3g Lys/g diet, respectively. These values evenly bracketed the predicted ideal Lys requirement. Slightly higher Lys requirement was found for optimum FE at 4 weeks and smaller fish, as opposed to 8 or 12 weeks and larger fish. Whole body composition was unresponsive to diet Lys level; however, higher dietary Lys was required to minimize liver size (4.8 to 5.2 g Lys/g diet) than to minimize body fat (2.5 to 3.1 g Lys /g diet) or maximize muscle ratio (1.8 to 3.9 g Lys/g diet). Whole body protein, lipid, energy, and EAA retentions were also consistent with cubic functions that generally confirmed the predicted ideal Lys requirement with notable exceptions. Retention of Lys decreased exponentially with increasing dietary Lys, whereas, met retention decreased in a linear fashion, corroborating that Met was first-limiting in this diet formula, as predicted. Retention of Thr and branched-chain amino acids were optimized at higher Lys levels (3.9-4.5 g/g diet) than those required to maximize growth parameters. Protein accretion (g/fish/d) responded quadratically to Lys intake predicting maximum deposition at 0.10 to 0.16 g Lys/fish/d. Histological assessment of intestines in fish fed these high-soybean meal test diets did not reveal any lesions associated with enteritis for any diet and overall normal intestinal morphology was observed in all fish sampled.