Adaptability of probiotic bacteria is an important trait for the survival and colonization in water or fish intestine and the performance of their bio-control function. Bacillus is a widely used genus of probiotic bacteria in aquaculture. However, its survival dynamics and effect on water or fish intestine is still unclear. In this study, we assessed the survival dynamics of exogenous Bacillus subtilis Bst51 and its effect on the microbial community structure in water and fish intestine by using green fluorescent protein (GFP) labeling and bacteriological methods. Results showed that GFP labeling was an efficient method for detection of the survival of B. subtilis in the water column and fish intestine. Our results showed that when administered only once, the concentration of Bst51 in water declined to one-tenth of the original concentration and reached a stable state after 24 h. This confirmed that Bst51 strain was able to survive and colonize in aquaculture water with concentrations higher than 103 CFU (Colony Forming Units)/mL. The concentration of Bst51 cells in zebra fish intestine decreased slightly and remained constant at around 5×106 CFU/g after only one treatment. The results confirmed that if Bst51 cells have a concentration of over 109 CFU/mL they can survive and colonize in zebra fish intestine
