Bacillus S11 bacterium isolated from black tiger shrimp habitats was added to shrimp feed as a probiotic in three forms: fresh cells, fresh cells in normal saline solution, and a lyophilized form. After a 100-day feeding trial with probiotic supplemented and non-supplemented (control) feeds, Penaeus monodon (from PL30) exhibited no significant difference (p>0.05) in growth, survival nor external appearance between all three probiotic treatments, but significant differences (p