CLOSED CIRCULATORY-SYSTEM FOR MARICULTURE USING OZONE

In a closed circuit fish culture constructed of an ozone water purifying system, striped jack (Caranx delicatissimus) juveniles could be raised for more than 100 days without introducing fresh seawater. The water treatment process consisted of solid separation, ozonation, filtration with coral sand and activated carbon, and foam skimming. The bacteria counts, NH4+-N and NO2--N concentrations and COD in the fish tank water were maintained as low as 9.3 x 10(5) cells/mL, 0.46 mg/L, 0.04 mg/L, and 3.4 mg/L, respectively. Ammonia nitrogen was denitrified by oxidants which were produced during ozonation. In the decomposition of NH4+-N, the yield of NO3--N as a byproduct was less than 1%. Disinfection by ozonation and removal of organic pollutants using the foam skimmer were performed effectively in the system.