Vibriosis resistance induced by glucan treatment in tiger shrimp (Penaeus monodon)

Postlarval tiger shrimp (Penaeus monodon) were immersed in aerated beta-glucan suspensions for 3 h. Enhanced growth was observed in shrimp immersed in glucan at concentrations of 0.5, 1, and 2 mg/ml, but not at 0.25 mg/ml. Shrimp gill tissue became shrunken immediately after immersion in the 2 mg/ml suspension. On days 10, 18, and 43 after beta-glucan treatment, shrimp were immersed in a bacterial suspension containing Vibrio vulnificus cells at a concentration of 5×107 CFU/ml for 12 h at a density of 25 individuals per liter; deaths were recorded for one month following experimental infection. The protective effect of glucan treatment was observed in those shrimp treated with 0.5 and 1 mg/ml glucan, but not in shrimp treated with 0.25 and 2 mg/ml glucan. The protective effect lasted until day 18 following immersion. In vitro, beta-glucan treatment enhanced the phenoloxidase activity in shrimp hemocytes. It therefore appears that beta-glucan is a short-term immunostimulant for shrimp.