The dietary lysine requirement for optimum protein retention differs with rainbow trout (Oncorhynchus mykiss Walbaum) strain

Authors: LEE, SEUNGHAN - University Of Idaho; SMALL, BRIAN - University Of Idaho; PATRO, BISWAMITRA - University Of Idaho; Overturf, Kenneth - Ken; HARDY, RONALD - University Of Idaho

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2019
Publication Date: 9/6/2019
Citation: Lee, S., Small, B., Patro, B., Overturf, K.E., Hardy, R. 2019. The dietary lysine requirement for optimum protein retention differs with rainbow trout (Oncorhynchus mykiss Walbaum) strain. Aquaculture. 514. https://doi.org/10.1016/j.aquaculture.2019.734483.
DOI: https://doi.org/10.1016/j.aquaculture.2019.734483

Interpretive Summary: Aquaculture is the fastest growing sector of animal aquaculture and feed costs can be as high as 70% of production costs. Traditional feeds consisted of fishmeal as the primary protein source but since fishmeal is a finite resource and cannot meet current protein requirements for aquaculture feed there has been substantial efforts put forth to identify alternative protein replacements. Plant proteins have been identified as the future protein source for aquaculture feeds, however plant proteins do not possess sufficient levels of certain necessary components, such as essential amino acids. A feeding trial was conducted to compare the nutritional requirement of a fast-growing strain and a slow-growing strain of rainbow trout evaluating effect of amino acid supplementation. Diets containing low levels of fishmeal were formulated and supplemented with the essential amino acid lysine at varying levels. Each diet was fed to three replicate tanks of each strain to satiation three times daily. After 12 weeks of feeding, the fast-growing strain had significantly higher weight gain and daily feed intake than the slow growing stain. The addition of dietary lysine significantly improved body weight gain and other calculated indices of weight gain in both strains when added. Significant differences between strains were found for protein retention, indicating differences in lean body weight gain. Our findings showed that the levels of other essential amino acids increased in a relatively equal manner with the levels of lysine added to the diet. The results from this study show that the dietary lysine requirement of rainbow trout for optimum lean-body growth and protein retention differs with fish strain and is independent of feed intake. This research is important for producers and feed manufacturers as they can now use this information collaboratively to modify the fish strains reared with the nutrient components of the feed to ensure optimal and economical growth.

Technical Abstract: A 12-week feeding trial was conducted to compare the dietary lysine requirement of a fast-growing strain (FGS) and a slow-growing strain (SGS) of rainbow trout, Oncorhynchus mykiss. Five isonitrogenous (37% digestible protein) and isocaloric (17.6 MJ kg-1 of digestible energy) diets were formulated and supplemented with L-lysine HCl in increments of 0.40% (1.80, 2.20, 2.60, 3.00 and 3.40% diet) resulting in analyzed lysine values of 1.83 (Lys1.83), 2.20 (Lys2.20), 2.67 (Lys2.67), 3.06 (Lys3.06) and 3.52 (Lys3.52) g/100g diet, respectively. Juvenile rainbow trout from the FGS (initial weight 12.2±0.3 g) and the SGS (initial weight, 8.54±0.19 g) were randomly stocked to 145-L tanks, each containing 35 fish per tank, in a 2 x 5 factorial design. Each diet was fed to three replicate tanks of each strain to apparent satiation three times daily. After 12 weeks of feeding, the FGS had significantly higher weight gain and daily feed intake (g/fish) than the SGS. No significant diet x strain interactions were detected. Dietary lysine significantly improved body weight gain and other calculated indices of weight gain in both strains up to 2.20% dietary lysine, but not higher. However, significant differences between strains were found in protein retention, indicating differences in lean body weight gain. Using broken-line regression analysis of protein retention, the optimum dietary lysine level for the FGS and SGS were 2.75 (6.18) and 2.23 (5.01) % of diet (% of dietary protein), respectively. Lysine retention decreased with increasing dietary levels in both strains. Whole body content of essential amino acids, with the exception of arginine, showed significant increases with dietary lysine levels in both strains of rainbow trout. Liver aspartate transaminase activity significantly increased with increasing dietary lysine, but alanine transaminase activity was not significantly affected by dietary lysine in either strain. The results show that the dietary lysine requirement of rainbow trout for optimum lean-body growth and protein retention differs with fish strain and is independent of feed intake.