Abstract:
Accumulation of ammonia, nitrite and hydrogen sulfide in shrimp pond is generally caused byresidual organic matters from overfeeding and from organic wastes released by shrimps. Thephenomenon effects to shrimp growth and survival rate. The objectives of this research were toscreen for a bacterial strain able to digest organic residues in shrimp pond and to evaluate thechanges of residues by bacterial activites. The results from this investigation showed that theisolated strain, Bacillus cereus S1, had the highest protease activity (57.1 U/ml) with highglucoamylase and lipase (4.5 and 0.33 U/ml, respectively). Under an aseptic condition with 0.1%shrimp feed, B.cereus S1 and the mixture of this B.cereus S1 and a water sample from nitrificationpond were able to degrade organic matters and significantly reduce chemical oxygen demand(COD) (70.8% and 83.4%, respectively). However, similar changes of NH+4-N (ammonia-nitrogen),NO-3-N and NO-2-N (nitrite-nitrogen) from both conditions were observed. Undernatural conditions with 0.05% shrimp feed and 0.05% sediment, B.cereus S1 and a commercialbacterial product (Inpicin-G) reduced COD (4.5% and 15.8%, respectively) and BOD (35.1 and11.4%, respectively). However, similar changes of NH+4-N, NO-3-N, NO-2-N and protein content inwater sample from the conditions were observed. Toxin production test indicated that, B.cereus S1produced a very small amount of toxin compared to toxin standard. Therefore, the bacterium,Bacillus cereus S1, could be applied to decrease organic matters accumulated in shrimp pondsediment without any harms to shrimps or consumers.