Dietary L-Lysine Requirement of Coho Salmon (Oncorhynchus kisutch) Alevins.

Simple Summary: With the increasing demand for aquaculture, the resource of high-quality traditional protein (such as fishmeal) becomes limited, and plant ingredients are often used as substitutes for fishmeal because of their low price and wide availability. However, plant proteins are usually deficient in certain essential amino acids (EAAs), which adversely affects the growth performance of aquatic animals. Lysine is generally the first limiting amino acid in plant protein ingredients used to formulate the aquafeed, and it plays an important role in physiological processes including antioxidant, differentiation, growth, immunity, and reduction of nitrogen emission. In this study, the effects of dietary graded L-lysine concentrations on the growth, proximate composition, and AA (amino acid) profile of coho salmon alevins were evaluated by a feeding trial. The results showed that an adequate dietary lysine level significantly improved the specific growth rate (SGR), protein efficiency ratio (PER), body protein deposition (BPD), and feed conversion ratio (FCR). The dietary optimum L-lysine requirements for coho salmon alevins were 3.74%, 3.73%, 3.91%, and 3.77% of the diet or 6.80%, 6.78%, 7.11%, and 6.85% of dietary proteins against the SGR, PER, BPD, and FCR, respectively. The suitable dietary L-lysine concentration for coho salmon (Oncorhynchus kisutch) alevins was assessed by a dose response feeding trial. Six experimental diets were made with graded L-lysine concentrations of 2.29%, 2.81%, 3.32%, 3.80%, 4.27%, and 4.78% of the dry matter, respectively, each of which was fed to triplicate groups of 100 alevins (initial body weight: 0.30 ± 0.01 g) in 18 plastic baskets (water volume 240 L). The alevins were cultured in a flowing freshwater system and fed manually to apparent satiation four times a day for 12 weeks. The survival rate of alevins did not differ significantly among the dietary groups. The specific growth rate (SGR), protein efficiency ratio (PER), and body protein deposition (BPD) increased significantly (p < 0.05) with the increase in dietary lysine concentration up to 3.80% and then reduced as lysine level further increased. The feed conversion ratio (FCR) had an inverse trend to SGR. The whole-body crude protein content of the alevins increased significantly with increasing dietary lysine level, while crude lipid content showed the opposite trend. In comparison, the contents of morphological indices, whole-body moisture, and ash were not affected significantly (p > 0.05) by the different dietary lysine concentrations. The highest contents of lysine, arginine, and total essential amino acids (EAAs) were observed in the group with 4.27% dietary lysine concentration, which did not differ significantly from those in the 3.32%, 3.80%, and 4.78% groups but was significantly higher than those in the 2.29% and 2.81% groups. Similarly, valine had the highest content in the group with 4.78%. The variations in dietary lysine had no significant impacts on other EAA and non-EAA contents except glycine, which increased with increasing dietary lysine level. Second-order polynomial model analyses based on SGR, PER, BPD, and FCR evaluated the optimum L-lysine requirements of coho salmon alevins as 3.74%, 3.73%, 3.91%, and 3.77% of the diet or 6.80%, 6.78%, 7.11%, and 6.85% of dietary proteins, respectively. [ABSTRACT FROM AUTHOR]