Evaluation of potential probiotics isolated from saline tilapia in shrimp aquaculture

Integration of tilapia to shrimp culture is currently being practiced to minimize the growth of pathogenic luminous bacteria. The microorganisms that are associated in tilapia may contribute to the inhibition of the growth of Vibrio harveyi through the production of secondary metabolites. In this study, two Bacillus strains (MJA1.1, MJA2.1) isolated from mucus of tilapia were evaluated for their possible application in shrimp culture. The inhibitory property of these isolates against V. harveyi was determined in vitro using co-culture assay in a liquid medium. Also qualitative extracellular enzyme assay was conducted to assess whether the bacterial isolates produce extracellular enzymes. Furthermore, the potential use of these isolates as shrimp feed additive was tested. Thereafter, shrimps were exposed to lethal dose of ammonia (140 mg l(-1)) to test the effects of the isolates in vivo. The results showed that in vitro co-culture assay after 72 h caused a significant decline in the population of V. harveyi in treatments with potential probiotic isolates. Both isolates showed protease, amylase, and cellulase activities. Although no significant difference was observed in growth, survival was significantly higher in shrimp fed with diets added with either of the isolates. The shrimp exposed to lethal dose of ammonia demonstrated better survival when supplemented with the probionts compared to the control group. Thus, the efficiency of the isolates in inhibiting V. harveyi population and the improvement of survival and resistance of cultured shrimp to ammonia stress indicate their potential as probionts for shrimp culture.