Alteromonas sp. S9730 cultured in 20% dilution of marine broth can produce antibacterial substance againts pathogenic V. harveyi 1526. Their fresh cells can also inhibit virulent V. harveyi 1526 in seawater. Alteromonas sp. S9730 showed antibacterial activity against shrimp pathogenic bacterias: V. harveyi 6 strains, V. parahaemolyticus, V. vulnificus, and non-pathogenic V. alginolyticus by using a double layer method. Adding Alteromonas sp. S9730 at 10x10x10x10x10x10x10 CFU/ml in the culture water did not increase survival of Penaeus monodon in the 3 different stages studied: zoea, mysis, and postlarvae. However, after challenging by immersion with V. harveyi 1526, shrimp larvae in mysis stage showed significantly higher survival rate than those of the control group (p<0.05) but no different survival rates among the treatment and the control groups in zoeal and postlarval stages were found.
