Performance of a closed recirculating system with foam separation, nitrification and denitrification units for intensive culture of kuruma shrimp, Marsupenaeus japonicus: a bench scale study

The development of a closed recirculating aquaculture system that does not discharge effluents would reduce a large amount of pollutant load on aquatic bodies. In this study,kuruma shrimp Marsupenaeus japonicus were reared in a closed recirculating system (total water volume, 1.3 m3), which consisted of a culture tank (area, 1.2 m2), a foam separation unit, a nitrification unit and a denitrification unit. The foam separation unit has an inhalation-type aerator and supplies air bubbles to the culture water. The shrimp used in the test (0.8g.individual- 1) were judged in advance to be free of the white spot disease virus (WSDV) by the method of loop-mediated isothermal amplification (LAMP). The growth of shrimp, which were fed a commercial diet, was satisfactory, with the average weight increases of up to 11 times in 4.5 months. The individual density at the end of the culture period was 51 individuals.m-2. The foam separation unit maintained oxygen saturation in the water used for rearing at 101%. Furthermore, contaminants such as suspended solids, chromaticity substances and bacteria absorbed on the stable foam were removed from the culture water by foam separation. The turbidity in culture water was kept at less than two units. Total ammonia-nitrogen (TAN) and nitrite (NO2-N) oxidation were accomplished rapidly and simultaneously in the nitrification unit. TAN and NO2-N concentrations were kept at less than 0.4 mg-N.L-1 and 0.02 mg-N.L-1, respectively. When the denitrification process was operated, nitrate (NO3-N) that accumulated in the culture water (20 mg-N.L-1) was reduced to 4 mg-N.L-1. Based on these results, the intensive aquaculture of kuruma shrimp can be achieved using a closed recirculating system under virusfree conditions without emission.