Dietary glycine supplementation improves the growth performance of 110- to 240-g (Phase-II) hybrid striped bass (Morone saxatilis ♀× Morone chrysops ♂) fed soybean meal-based diets.

We recently reported that supplementing glycine to soybean meal (SBM)-based diets is necessary for optimum growth of 5- to 40-g (Phase-I) hybrid striped bass (HSB). The present study tested the hypothesis that supplementing glycine to SBM-based diets may enhance the growth of 110- to 240-g (Phase-II) HSB. HSB (the initial body weight of approximately 110 g) were fed a SBM (58%)-based diet supplemented with 0%, 1%, or 2% of glycine, with L-alanine serving as the isonitrogenous control. There were 4 tanks per dietary group, with 4 fish/tank. The fish were fed their respective diets to apparent satiation twice daily. The feed intake and body weight of fish were recorded daily and every 2 wk, respectively. At the end of the 56-d feeding trial, plasma and tissue samples were collected to determine amino acid concentrations and histological alterations, and tissues were used to measure the oxidation of L-glutamate, L-glutamine, L-aspartate, and glycine. Results showed that dietary supplementation with 1% and 2% glycine dose-dependently increased (P ˂ 0.05) the concentration of glycine in the plasma of HSB by 48% and 99%, respectively. Compared with the 0%-glycine group, dietary supplementation with 1% glycine did not affect (P ˃ 0.05) the feed intake of HSB but increased (P ˂ 0.05) their final body weight, weight gain, and gain:feed ratios during the whole period by 13%, 29%, and 21%, respectively. Compared with the 1% glycine group, dietary supplementation with 2% glycine increased (P ˂ 0.05) the feed intake, final body weight, and weight gain of HSB by 13%, 7%, and 14%, respectively. Compared with the 0%-glycine group, fish fed the 1%-glycine and 2%-glycine diets had a greater (P ˂ 0.05) villus height in the proximal intestine, when compared with the 0%-glycine group. Collectively, these results indicated that SBM-based diets did not provide sufficient glycine for Phase-II HSB (110 to 240 g) and that dietary glycine supplementation is essential for their optimum growth and intestinal structure.