Effect of Graded Levels of Dietary L-Methionine on Growth Performance, Body Composition, Amino Acid Requirements, Serum Biochemical Parameters and Gut Microbiota in Coho Salmon (Oncorhynchus kisutch) Alevins Cultured in Freshwater

Abstract

This study aimed to evaluate the methionine requirement of coho salmon (Oncorhynchus kisutch) alevins. A total of 1,800 alevins (initial body weight: 0.338 +/- 0.002g) were used in the experiment, distributed across six dietary treatments with three replicates per treatment and 100 alevins per replicate. Six dietary concentrations levels of L-methionine were as follows: 1.09%, 1.64%, 2.15%, 2.63%, 3.14%, and 3.67% of the feed, or 1.98%, 3.01 %, 3.91%, 4.75%, 5.74% and 6.66% of the feed protein. ANOVA test was applied to statistically analyze the data. The results of the study revealed that body weight and specific growth rate were higher at 2.15% methionine level. While body protein increased with the increase of methionine level in the feed, reaching the highest (P<0.05) level at 2.63% methionine, the arginine content was significantly lower at 1.09% and 1.64% levels; the lysine and methionine content was significantly higher at 2.15% and 2.63% methionine levels. Body fat, ash content, and essential amino acid requirements were nonsignificant. Significantly higher ALT, aspartate AST, Lactobacillus, and Bacillus, and lower (P<0.05) total cholesterol and triglyceride, Coliform, and Vibrio were recorded in 2.15% and 2.63% L-Methionine group. It was concluded that dietary L-methionine levels of 2.15% and 2.63% effectively enhanced performance, body composition, serum biochemical parameters, and gut microbiota in coho salmon alevins. Furthermore, the quadratic polynomial model analysis indicated that a methionine requirement between 2.55% and 2.69% is optimal for achieving the best results in specific growth rate, feed conversion ratio, protein efficiency ratio, and body protein deposition.