Improved growth rate and disease resistance in farmed Haliotis midae through probiotic treatment

The use of probiotics in aquaculture is proving to be highly effective in improving disease resistance, nutrition and/or growth of cultured organisms. We have shown that Haliotis midae fed a probiotic-supplemented diet have an improved survival and growth rate compared to animals not fed probiotics. The growth rate of small (20 mm) and large (67mm) abalone was improved by 8% and 34%, respectively, in two separate eight-month farm growth trials. Furthermore, the number, and phagocytic activity, of circulating haemocytes was significantly higher (P<0.05) in probiotic treated animals compared to non-treated animals following challenge with the pathogenic bacterium Vibrio anguillarum. Seven days after challenging with V. anguillarum, the probiotic-fed animals had 62% survival compared to 25% survival for non-treated animals. In situ protease assays showed that probiotic treatment significantly increased (P<0.05) protease activity in the intestinal region of the digestive tract of animals fed the probiotic-supplemented feed. This correlated with a significant increase (P<0.05) in the amount of protein digestion and absorption measured in this region of the abalone gut. Histological analysis showed that the digestive glands of animals receiving probiotics were bacteria-free, whereas the digestive glands of 70% of the animals receiving the non-supplemented feed had a high bacterial load. The microorganisms tested in this study therefore have tremendous potential as probiotics for commercially produced H. midae.