Dietary β-1,3-glucan effectively improves immunity and survival of Penaeus monodon challenged with white spot syndrome virus

The effectiveness of dietary beta-1,3-glucan (BG), derived from Schizophyllum commune, in modulating the non-specific immunity of the grass prawn Penaeus monodon and its resistance to white spot syndrome virus (WSSV) were investigated. Juvenile P. monodon (6.5 +/- 0.4 g) were fed for 20 days on a series of test diets containing graded levels of BG (0, 1, 2, 10, 20 g kg(-1) diet) and were then challenged by injection of WSSV. The haemolymph total haemocyte count (THC), phagocytosis (PI), phenoloxidase (PO), superoxide anion (O-2(-)) and superoxide dismutase (SOD) production were measured at days 0, 1, 3, 6, 9, 12 and 24 after challenge, and shrimp survival rate was also recorded. All the shrimps fed on diets containing BG no more than 1 g kg(-1) died by day 12. Conversely, the survival rate of shrimp fed with the diet containing 10 g kg(-1) BG was significantly higher (P < 0.05) by day 9 than that of the other groups. When screened by the WSSV PCR diagnostic procedure, the percentages of surviving juveniles of the BG 2, 10, 20 g kg(-1) groups that were 2-step WSSV negative, were 55, 65 and 65%, respectively. The haemolymph THC, PO, O-2(-) and SOD production of the 2, 10 and 20 g kg(-1) BG diet groups dropped drastically immediately after the WSSV challenge but subsequently returned to normal. Therefore, oral administration of BG at an optimal level of 10 g kg(-1) diet for 20 days effectively enhanced the immune system and improved the survival of WSSV-infected P. monodon. (C) 2003 Elsevier Ltd. All rights reserved.