Abstract:
The closed recirculating seawater system for an indoor black tiger shirmp cultivation was consisted of; (1) round-shape shrimp tank with 3 m in diameter and 3,000 L in volume, (2) 5 microns cartridge filter, (3) protein and fat fractionator, (4) nitrification tank with a diameter of 2x2x1.25 m and 3,500 L in volume packed with Biopolyma [superscript TM] biofilter material and (5) Tubular Denitrification Reactor (TDR) made of 50 m length PVC pipes (1 inch in diameter) packed with 2,040 plastic bioballs. The denitrification reaction in TDR was automatically regulated using ORP controller in order to supply methanol as the carbon source for the bacteria. The experiment consisted of two identical seawater systems. High shrimp density (150 shrimp/m [superscript 2] and normal shrimp density (50 shrimp/m [superscript2] were applied to system 1 and 2 respectively. The P23 shrimps were cultivated for 132 days in 25 PSU seawater without water exchange throughout the culture period. The results show that the closed recirculating seawater system had very good performance in water quality control. With high-density shrimp tank, average total ammonia was 0.086+-0.05 mg-N/L (0.00-0.25 mg-N/L data range), average nitrite was 0.04+-0.047mg-N/L ( (0.009-0.23 mg-N/L) and average nitrate was 30.45+-9.08 mg-N/L (9.16-45.59 mg-N/L). On the other hand, normal-density shrimp tank had slightly lower inorganic nitrogen concentrations. With normal-density shrimp tank, average ammonia was 0.060+-0.05 mg-N/L (0.00-0.25 mg-N/L), average nitrite was 0.023+-0.018 mg-N/L(0.006-0.15 mg-N/L), and average nitrate was 23.29+-4.25 mg-N/L(14.46-34.49)mg-N/L). Growth of shirmp in both systems was not systems was not significant different. Weight of shrimp in the high-density tank increased from 0.13 g to 10.82 g with an average daily weight gain (DWG) of 0.081 g/d and feed conversion ratio (FCR) of 1.86. Weight of shrimp in the normal-density tank had slightly higher than that found in high-density tank. Average weight increase from 0.13 g to 11.96 g with DWG of 0.09 g/day and FCR of 1.71. Survival rate of shrimps was 51.1 and 51.7% in high and normal-density tank respectively. The results suggested that the closed recirculating seawater system could maintain good water quality throughout the experiment and eliminated the need of water exchange. Seawater in the tank after shrimp harvest could be reused for the next crop.