The potential effect of two beneficial bacteria - Azotobacter vinelandii and Bacillus megaterium – was studied in experimental tanks cultured with Penaeus monodon. The shrimps exhibited higher levels of production and growth rate, along with lower levels of food consumption and food conversion ratio, in the experimental tanks inoculated with the bacterial strains. There was also a significant reduction in the level of ammonia. All these beneficial effects were higher in the tanks treated with B.megaterium than A. vinelandii and mixed cultures.

KEY WORDS: Probiotic bacteria, Bacillus megaterium, Azotobacter vinelandii, Penaeus monodon, water quality, shrimp