Enhancement of the non-specific defence activities in carp (Cyprinus carpio) and flounder (Paralichthys olivcaces) by oral administration of schizophyllan

The effect of an immuno-stimulative beta-glucan from Schizophyllum commune, schizophyllan, on the enhancement of fish immunity was evaluated with carp and flounder. The oral administration of schizophyllan induced a reduction in cumulative mortality after a bacterial challenge. Whereas mortality in the control groups was 100% after seven days, it was only 60% after challenging carp (Cyprinus carpio) with 1 x 10(6) cells of Aeromonas hydrophila and 70% for flounder (Paralichthys olivaceus) using 1 x 10(6) cells of Edwardsiella tarda. The numbers of peripheral macrophages and neutrophiles, the phagocytic activities of leukocytes and the activity of serum lysozyme were increased in the fish being fed a schizophyllan-supplemented diet. These results support the findings that non-specific defence activities in fish such as the number of leukocytes, phagocytic activities and serum lysozyme activity could be enhanced by oral administration of schizophyllan. Moreover, the oral administration of schizophyllan can reduce mortality after bacterial infections depending on the size of fish and the concentrations of bacteria.