In this research microflora associated with the natural habitat of Macrobrachium rosenbergii, an important cultivated freshwater shrimp. Water, sediment and feed items of this shrimp were analysed to find out bacterial strains with potential to act as probiotic in the culture and rearing operations of this shrimp. Nearly 900 strains of bacteria were isolated from various samples were characterised and evaluated for their probiotic potential using standard methods. Two strains such as Bacillus NL 110 and Vibrio NE 17 which showed good probiotic potential were chosen for further studies. These strains were administered through water and feed to the young ones of Macrobrachium rosenbergii and improvements in growth and immunity were evaluated. Environmental microflora associated with farm raised Macrobrachium rosenbergii and those from the hatchery environment were also characterised and evaluated for their antibiogram. The results are presented as separate chapters after and introductory chapter on aquaculture and use of probiotics in aquaculture.