Effect of Immobilized Bacteria on Tan Suppression, Survival Rate, and Biomass Harvest of Pacific White Shrimp, Litopenaeus vannamei, Grown in Biofloc Culture System

In this study, immobilized bacteria (Nitrosomonas, Nitrobacter and Nitrospira) were added into three shrimp ponds in a concentration of 2x10⁶ cfu mL^-1 that equals to 20 kg beads ha^-1. The other three ponds were used as control treatment. All ponds were stocked with PL’s (Post Larvae) of Pacific white shrimp at a density of 100 PL’s m^-2. Shrimps were fed with a commercial diet containing 36% crude protein, 7% fat, 10% ash, and 2% crude fibre. Oxygen was kept near saturation through paddle-wheels. Secchi disc depth, pH and temperature were monitored daily. Total ammonia nitrogen (TAN), nitrite and nitrate were measured every 10 days together with sampling for shrimp body weight and feed adaptation. Average TAN concentration of ponds with nitrifying bacteria was 0.12±0.144 mg L^-1, one fourth of the control ponds (0.523±0.564 mg L^-1). Average nitrite concentration in control ponds (0.058±0.045 mg L^-1) was also significantly higher than the ponds added with immobilized bacteria (0.037±0.038 mg L^-1). However, the end product of nitrate was not significantly different (α = 0.607) among the ponds. Although not affecting shrimp growth, TAN suppression significantly increases the survival rate and finally resulted in higher (α = 0.043) biomass harvest, from 12.37 t ha^-1 (control ponds) to 18.87±2.91 t ha^-1 at treatment ponds. This study concluded the importance of transforming TAN concentration into nitrate, particularly in intensive culture system. To do this, the presence of immobile nitrifying bacteria is needed.