Effects of dietary live Bacillus sp. BC26 on digestive enzyme activity, immune response and disease resistance against Vibrio splendidus infection in juvenile sea cucumber Apostichopus japonicus

Juvenile sea cucumber Apostichopus japonicus was randomly divided into 12 plastic tanks of each filled with 100 L filtered sea water at a rate of 50 individuals per tank and fed basal diet( control group) and the basal diets containing bacterium Bacillus sp. BC26 at a dose of 105,107and 109CFU / g diet for 45 d with triplication. At the end of the feeding trial,effects of Bacillus sp. BC26 on digestive enzyme activity,immune response and disease resistance against Vibrio splendidus infection were studied in the sea cucumber fed the various diets. Results showed that there were significantly higher trypsin and lipase activities in the intestine,and phenoloxidase and total nitric oxide synthase activities in the coelomic fluid in the sea cucumber in the experimental groups than those in the control group( P0. 01). The sea cucumber fed the diet containing Bacillus sp. BC26 at 107and 109CFU / g diet had significantly higher phagocytic activity than the sea cucumber in the control group( P0. 01). Cumulative incidence and mortality of the sea cucumber fed the Bacillus sp. BC26 were found to be lower than those in the control group when 10 sea cucumber samples in each group were challenged with V. splendidus NB13. The findings show the supplementation of Bacillus sp. BC26 lead to improvement of digestive enzyme activity and the immune response of the sea cucumber juveniles,thus enhancing their resistance against V. splendidus.