Dietary glycine supplementation modulates antioxidant and immune responses of beluga, Huso huso, juveniles

Abstract

Glycine is a non-essential amino acid used in fish nutrition, and possess several important roles in physiological process. Despite such functions, little is known about the glycine roles in fish, particularly in sturgeons. Therefore, the present study aimed at assessing the effects of dietary glycine supplementation on growth performance, antioxidant, and immunological parameters in beluga, Huso huso. Four hundred eighty fish (~ 48 g) were randomly distributed in 12 fiberglass tanks (1200 L) at a stocking density of 40 fish per tank. Four diets supplemented with 0% (control), 0.25% (Gly0.25), 0.5% (Gly0.5), and 1% (Gly1) glycine were offered to the fish (each diet to a batch of three tanks) for eight weeks at water temperature of 23.2 ± 0.70 °C. At the end of the feeding trial, the fish were blood-sampled for blood leukocyte count, plasma cortisol, glucose, triglyceride, cholesterol, reduced glutathione (GSH), glutathione reductase (GR), glutathione peroxidase (GPx), malondialdehyde (MDA), lysozyme, and alternative complement activity (ACH50) analysis. The results indicated there were no significant differences in the fish final weight (197–213 g; P = 0.511), weight gain (299–311%; P = 0.956) specific growth rate (2.46–2.52%/d; P = 0.944), feed conversion ratio (0.97–1.03; P = 0.863), protein efficiency ratio (2.29–2.45; P = 0.775), and survival (91.7–100%; P = 0.306) among the treatments. Plasma cortisol level significantly decreased in Gly0.25 treatment, compared to the control (24.7 vs. 28.8 ng/mL; P = 0.035). Plasma glucose levels exhibited significant (P < 0.001) elevation in Gly0.5 (51.0 mg/dL) and Gly1 (53.0 mg/dL) treatments, compared to the control (42.0 mg/dL). The treatment Gly0.5 showed significant elevations in blood leukocyte count (11.4 vs. 8.23 ×1000cell/µL; P = 0.032), plasma triglyceride (581 vs. 410 mg/dL; P = 0.017), cholesterol (71.3 vs. 59.8 mg/dL; P = 0.011), GSH (2.67 vs. 2.21 mM/mL; P = 0.003), GPx (243 vs. 217 U/mL; P < 0.001), and MDA (123 vs. 99 mM/L; P < 0.001), compared to the control treatment. Plasma GR (P < 0.001) showed significant decrease in Gly0.5 (1154 vs. 1784 U/mL) and Gly1 (1171 vs. 1784 U/mL) treatments. Besides, Gly0.25 and Gly0.5 treatments showed significantly higher plasma lysozyme (45.8–45.9 vs. 36.5 U/mL; P = 0.001) and ACH50 (138–139 vs. 130 U/mL; P < 0.001), compared to the control. Based on the results, dietary glycine supplementation at 0.25–0.5% could suppress plasma cortisol levels and improve antioxidant and immunological parameters on beluga, although has no beneficial effects on the fish growth performance.