Bacillus as probiotics for aquatic species

Aquacultural output is now growing by over 7% per year, and is offering a vital opportunity to significantly help in meeting global food demand. However, disease and feed costs continue to pose a serious challenge to the industry, particularly in Asian fish and shrimp production. Recently-developed, reproducible in vivo methods, such as PCR-based quantification, in situ germination assays, and rapid histological evaluations have greatly accelerated the identification of effective direct-fed probiotic bacteria. Such bacteria are able to significantly increase growth, feed conversion and health of aquatic species. Certain specific spore-forming Bacillus strains have been found to germinate effectively in fish gut tissues of tilapia, pangasius, and trout and to significantly enhance microvilli length and density. In addition, via assessment of over 1,000 metabolites produced in the liver and plasma of treated fish, we have identified a subset of at least six novel bile acids that are induced in the fish liver by the presence of a specific direct-fed Bacillus strain. An increase in fillet weight of 8-11% in fish fed one of these Bacillus has been observed in pangasius and tilapia. However, no microvilli or filet-weight enhancement was observed for at least one other Bacillus strain, despite effective gut germination and presence, or in non-treated controls. In addition, separate probiotic Bacillus strains proved capable in tank studies of protecting shrimp from the highly virulent bacterial disease EMS (Early Mortality Syndrome) caused by Vibrio parahaemolyticus.