Effect of dietary β-glucan on blood metabolites and immunity of Litopenaeus vannamei at low salinities

In order to study the effects of long-term feeding β-1,3-glucan on blood metabolites and muscle immune related enzyme activities of cultured Litopenaeus vannamei at low salinity (5), we fed the fish with initial body mass of (0.65 ± 0.01) g with four diets containing 0, 250, 500 and 1 000 mg·kg⁻¹ β-1,3-glucan, respectively, for 84 d. The results show that the highest values of serum lactate and muscle lysozyme activity appeared on the 14^th day after ingestion. Levels of total protein, glucose, cholesterol and triglyceride reached their maximum levels at 42^nd day. Activities of superoxide dismutase, catalase and anti-O₂ ⁻ reached their maximum levels at 56^th day. The levels of glucose, cholesterol, triglyceride, lactate and superoxide dismutase were significantly higher in 250 mg·kg⁻¹ β-1,3-glucan-containing diets than those in the control diet (P<0.05). The contents of total protein and anti-O₂ ⁻ were significantly higher in 500 mg·kg⁻¹ β-1,3-glucan-containing diet than those in the control diet (P<0.05). The activities of catalase and lysozyme were significantly higher in 250 or 500 mg·kg⁻¹ β-1,3-glucan-containing diets than those in the control diet (P<0.05). Feeding 250 or 500 mg·kg⁻¹ β-1,3-glucan diets for 14, 42 or 56 d is recommended to improve shrimp's nutrition metabolism and immune ability.