Kewalee Chanpan, Sorwit Powtongsook, and Worapot Suntornsuk

pp. 89 - 99

Abstract

Accumulation of ammonia, nitrite and hydrogen sulfide in a shrimp pond is generally caused by incomplete degradation of residual organic matters from overfeeding and from organic wastes released by shrimps. The phenomenon affects shrimp growth and survival rate. The objectives of this investigation were
to screen for a bacterial strain able to digest organic residues and to evaluate the changes of residues by bacterial activities under natural conditions. The results from this work showed that the isolated strain, Bacillus cereus S1, had the highest protease activity (57.1 U/ml) with the presence of glucoamylase and lipase activities (4.5 and 0.13 U/ml, respectively). Under an aseptic condition in 1-L flasks containing seawater with 0.1% shrimp feed, B. cereus S1 degraded organic matters and significantly reduced chemical oxygen demand
(COD) (70.8%). An amount of ammonia-nitrogen was increased during the first 5 days of incubation due to the degradation of organic compounds in shrimp feed. However, it declined afterward with nitrate-nitrogen increase and unchanged nitrite-nitrogen content. Under natural conditions in 10-L glass jars containing seawater with 0.05% shrimp feed and 0.05% sediment, B. cereus S1 and a commercial bacterial product (Inpicin-G) could reduce COD (4.5% and 15.8%, respectively) and biochemical oxygen demand (BOD) (35.1
and 11.4%, respectively). However, similar changes of ammonia-nitrogen, nitrate-nitrogen and nitrite-nitrogen contents in water samples were observed. The results indicate that this selected bacterium could reduce organic compound accumulations on a laboratory scale. In addition, the strain did not produce any enterotoxins compared to a toxin standard. Therefore, the bacterium, Bacillus cereus S1, could be applied to decrease organic matters accumulated in shrimp pond without any harm to shrimps or consumers.