Abstract
Fish production in closed recirculating systems, which makes reduced discharge of organic and inorganic wastes possible, is considered to be one of the promising approaches for sustainable development of aquaculture. We have been conducting research on the closed production of Japanese flounder Paralichthys olivaceus since 1986 and developed a pilot scale culture system of 10m3 in total water volume. The system consists of a fish tank of 4m in diameter, settling tank, drum screen filter, submerged biological filter, heating-cooling unit, oxygen generator and supplier, blower, and UV-sterilizer. In the feeding experiment, 1015 fish of 2g initial body weight were introduced to the fish tank and fed commercial pellet diet twice daily to satiation. Fish grew to 456g after 259 days with good survival rate (85%) and feed efficiency (97%). Culture density at the end was 31kg/m2; the bottom area of the fish tank and total culture water used was 25m3. Dissolved oxygen ranged from 90 to 130% of saturation through the rearing period. Ammonia and nitrite were maintained at less than 4mg-N/L and no apparent adverse effects on the feeding and growth were observed.
