Effect of dietary beta-1,3 glucan on immune responses and disease resistance of healthy and aflatoxin B-1-induced immunocompromised rohu (Labeo rohita Hamilton)

The immunostimulant beta -1,3 glucan was fed at 0-1% in feed for 7 days to healthy and aflatoxin B-1 (AFB(1))-induced immunocompromised fish, Labeo ro hita (one of the major tropical carp species), in a 60 day trial. The effec ts of AFB(1), glucan and their interactions on non-specific and specific im munity levels and disease resistance of fish were studied. A single intrape ritoneal injection of AFB(1) at 1.25 mg kg(-1) body weight) caused a signif icant (P <0.05) reduction in non-specific immunity as measured through neut rophil phagocytic indices, serum bactericidal activity, and specific immuni ty as measured through bacterial agglutination titre against Edwardsiella t arda, as well as reduced protection against Acromonas hydrophila challenge in comparison to control fish which were exposed neither to aflatoxin nor t o glucan. Feeding of glucan to healthy fish raised the non-specific and spe cific immunity level and protection against bacterial infection compared wi th the control. Feeding of glucan to AFB(1)-induced immunocompromised fish for 7 days significantly raised the degree of resistance against A. hydroph ila challenge and the non-specific immunity level in comparison to non-trea ted AFB(1) exposed fish. Although feeding of glucan was able to increase sp ecific immunity, al measured through haemagglutination titre against sheep red blood cells, and bacterial (E. tarda) agglutination titre in healthy fi sh in comparison to all other groups, no significant increase in specific i mmunity to the aflatoxin-exposed group was seen. (C) 2001 Academic Press.