Effect of long-term administration of dietary β-1,3-glucan on growth, physiological, and immune responses in Litopenaeus vannamei (Boone, 1931)

beta-1,3-Glucan at different dietary doses was administered to enhance the growth, immunity, and survival against nitrite stress in Pacific white shrimp, Litopenaeus vannamei. Four different diets supplemented with 0, 250, 500, or 1,000 mg of beta-1,3-glucan kg(-1) diets were fed to L. vannamei. Growth performance (weight gain and survival rate), physiological conditions (blood total protein, glucose, lactate, triacylglycerols, cholesterol levels) and immunological responses (superoxide dismutase, catalase, lysozyme, acid phosphatase, and alkaline phosphatase activities) of shrimp were recorded after 84-day feeding and 120 h after exposed to nitrite-N. After 84-day feeding, 250 mg kg(-1) beta-1,3-glucan diet resulted in better weight gain (P < 0.05). Before the nitrite stress, blood lactate, triacylglycerols, and cholesterol level in shrimp fed with 250 mg kg(-1) beta-1,3-glucan diet were significantly higher than those observed in shrimp fed with other diets (P < 0.05). Higher activities of catalase, lysozyme, and alkaline phosphatase were observed in shrimp fed with 500 or 1,000 mg kg(-1) beta-1,3-glucan diet as compared to those obtained in shrimp fed with other diets (P < 0.05). After 120-h nitrite stress, blood protein, lactate, superoxide dismutase, catalase, and alkaline phosphatase activities in shrimp fed with 500 or 1,000 mg kg(-1) beta-1,3-glucan were significantly higher than those observed in shrimp fed with other diets (P < 0.05). Glucose and triacylglycerol levels of shrimp fed with 500 or 1,000 mg kg(-1) beta-1,3-glucan were significantly lower than those observed in other diets (P < 0.05). In shrimp fed with 500 and 1,000 mg kg(-1) beta-1,3-glucan and 120-h after nitrite stress, the mortality was significantly lower than that observed in shrimp of control. Together, in this 84-day feeding trial, 250 mg kg(-1) beta-1,3-glucan improved growth, whereas 500 mg kg(-1) beta-1,3-glucan preferentially improved nitrite resistance, probably through accelerating energy metabolism and activating immune system.