However, Shariff et al. (2001) found that treatment of P. monodon with a commercial Bacillus probiotic did not significantly increase survival. It was difficult to directly assess different studies using probiotics, because the efficacy of a probiotic application depended on many factors ( Gomez-Gil et al., 2000) such as species composition, application level, frequency of application and environmental conditions. Moreover, there was no significant difference between T-2 and T-3. This indicates that the quantity of probiotics was only one of the factors promoting the survival rate of shrimp larvae.