THE ACTIVITIES of NH4+ and NO2- OXIDIZING BACTERIA IN A RECIRCULATING AQUACULTURE SYSTEM FOR MUD CRAB (Scylla serrata) CULTURE
The culture of mud crab Scylla serrata in a recirculating system involves the microbiological nitrogen nitrogen removal including aerobic and anaerobic nitrogen conversion such as nitrification and denitrification. The concentrations of ammonia, nitrite and nitrate are increasing with the age of the cultured biota, and this could contribute to the animal's survival. The objective of this study was to isolate and to determine the activities of ammonia and nitrite oxidizing bacteria in crab culture using recirculating aquaculture system using two different quantity of shelters (0, 4 and 6 shelters). Ammonia and nitrite oxidizing activities tests was be used to determine the enzyme activity and affinity in the culture substrate . Based on Michelis Menten kinetics analysis for ammonia oxidizer, it was found that treatment P4 showed Vmax value (Maximum speed) of 0.073 µM/h and the Km (Michelis-menten Constant) of 0.1909µM/h. Whereas treatment P6 showed smaller values, i.e. Vmax of 0.0673 µM/h and Km of 0.0788 µM/h indicating that the affinity of enzymes related to ammonia oxidation by the bacteria in this treatment was higher. This was supported by the higher ammonia oxidation rate (12.72 ± 5.89 µM/h).