Dietary glycine supplementation enhances the growth performance of hybrid striped bass (Morone saxatilis ♀× Morone chrysops ♂) fed soybean meal-based diets

Abstract

This study was conducted to test the hypothesis that supplementing 1% and 2% glycine to soybean meal (SBM)-based diets can improve the growth performance of juvenile hybrid striped bass (HSB). The basal diets contained 15% fishmeal and 58% SBM (DM basis). Alanine was used as the isonitrogenous control in different diets. All diets contained 44% crude protein and 10% lipids (DM basis). There were four tanks (15 fish per tank) per dietary group, with the mean of the initial body weight (BW) of fish being 5.3 g. Fish were fed to apparent satiation twice daily, and their BW was recorded every 2 wk. The trial lasted for 8 wk. Results indicated that the BW, weight gain, protein efficiency ratio, and retention of dietary lipids in fish were enhanced (P < 0.05) by dietary supplementation with 1% or 2% glycine. In addition, dietary supplementation with glycine did not affect (P > 0.05) the feed intake of fish but increased (P < 0.05) the retention of dietary nitrogen, most amino acids, and phosphorus in the body, compared to the 0% glycine group. Dietary supplementation with 1% and 2% glycine dose-dependently augmented (P < 0.05) the villus height of the proximal intestine and reduced the submucosal thickness of the gut, while preventing submucosal and lamina propria hemorrhages. Compared with the 0% glycine group, dietary supplementation with 1% or 2% glycine decreased (P < 0.05) the proportion of skeletal-muscle fibers with diameters of 40 to 60 µm but increased (P < 0.05) the proportion of skeletal-muscle fibers with diameters of 80 to 100 µm and > 100 µm. Collectively, these findings indicate that glycine in SBM-based diets is inadequate for maximum growth of juvenile HSB and that dietary supplementation with 1% or 2% glycine is required to improve their weight gain and feed efficiency. Glycine is a conditionally essential amino acid for this fish.

Keywords: amino acids; fish; glycine; growth; health; nutrition.

Figure 1.

The sampling sites of the proximal intestine and skeletal muscle in juvenile hybrid striped bass.

Figure 2.

Histological analysis of the proximal intestine of juvenile hybrid striped bass fed glycine-supplemented diets for 8 wk. The tissues were stained with hematoxylin and eosin. Fish received dietary supplementation with 0%, 1%, or 2% glycine for 8 wk beginning at 5.3 g of body weight. Alanine was used as the isonitrogenous control. On day 56 of the experiment, the proximal intestine was obtained from the fish at 4 h after feeding. White arrow: submucosal and lamina propria hemorrhages; Black arrow: thickened submucosa. Gly-0%, Gly-1%, and Gly-2% denote dietary supplementation with 0%, 1%, and 2% glycine, respectively.

Figure 3.

Histological analysis of the skeletal muscle of juvenile hybrid striped bass fed diets with different levels of glycine. The tissues were stained with hematoxylin and eosin. Fish received dietary supplementation with 0%, 1%, or 2% glycine for 8 wk beginning at 5.3 g of body weight. Alanine was used as the isonitrogenous control. On day 56 of the experiment, skeletal muscle was obtained from the fish at 4 h after feeding. White arrow: small newly recruited fibers formed by mosaic hyperplasia; Black arrow: older larger fibers.