Effects of a probiotic mixture (Bacillus subtilis YB-1 and Bacillus cereus YB-2) on disease resistance and non-specific immunity of sea cucumber, Apostichopus japonicus (Selenka)

The effect of a commercially available compound probiotics product containing Bacillus subtilis YB-1 (50%) and Bacillus cereus YB-2 (50%) fed to sea cucumbers, Apostichopus japonicus (Selenka) on challenge infections and non-specific immune responses was assessed. Sea cucumbers (were randomly allocated into nine aquariums at a density of 30 sea cucumbers per tank and triplicate groups) were fed diets containing 0 (control), 10(7) and 10(10)cfu (g diet)(-1) of the probiotics mixture for 32days. The growth factors and immunological parameters were measured. In addition, the effects on resistance against Vibrio alginolyticus infection were also evaluated. The results indicate that all the immunological parameters (phagocytic activity, superoxide anion production, lysozyme activity, catalase activity and phenoloxidase activity) measured and the growth rate of sea cucumbers fed 10(10)cfu of the probiotics mixture were significantly (P<0.05) improved than control groups at 16 and 32days. After challenging, the cumulative mortality for the control was 100%, whereas the cumulative mortality for sea cucumbers fed 10(10)cfu of the probiotics mixture was 47% (P<0.05). Although the total autochthonous intestinal heterotrophic bacterial counts were not affected by dietary treatment (P>0.05), Bacillus sp. levels were significantly elevated in sea cucumbers fed the probiotics mixture (P<0.05). These results confirmed that administration of the probiotics mixture in the diet stimulated non-specific immune responses and enhanced the growth performance of sea cucumbers, and was effective in controlling infections caused by V.alginolyticus.