This study was conducted to estimate dietary valine (Val) requirement for juvenile olive flounder (Paralichthys olivaceus). In a feeding trial, a total of 540 fish (initial body weight: 23.0 ± 0.2 g) were stocked into 18 tanks (210 L). Six experimental diets containing graded levels of Val (4, 8, 12, 16, 20, and 24 g/kg, dry matter basis) were fed to the fish in triplicate groups for 13 weeks. The lowest growth, feed utilization, and survival were observed in 4 g/kg Val group (P < 0.05). Dietary Val deficiency resulted in significant decreases (P < 0.05) in whole-body protein and Val concentrations, hepatosomatic index, condition factor and plasma protein and cholesterol levels. Nonspecific immunity and antioxidant activities were significantly lower (P < 0.05) in 4 g/kg Val group than in other groups. Dietary Val deficiency upregulated the expression of proinflammatory cytokines and downregulated the expression of anti-inflammatory cytokines and intestinal tight junction protein (occludin) (P < 0.05). Mucosal fold height and submucosa and muscularis thickness of fish intestine were significantly lower (P < 0.05) in fish fed 4 g/kg Val diet. Relatively lower lipid droplet in hepatic cell was observed in 4 g/kg Val group. Our findings suggested that dietary Val requirements for juvenile olive flounder would be 17.7–18.9 g Val/kg (35.4–37.8 g/kg on the basis of crude protein), estimated by quadratic regression analysis based on the weight gain, protein efficiency ratio, and protein retention efficiency.
Aquaculture Nutrition, Volume 2024, Issue 1, 2024. Read More