Abstract
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.
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