Rearing experiment with Japanese flounder, Paralichthys olivaceus, was carried out within a closed recirculating system of 22m³ in total water volume. At the start of the experiment, 2000 flounder of 3.5g in average body weight were introduced to the system and fed a commercial pellet diet to apparent satiation twice daily. Fish grew to an average weight of 480g and had a survival rate of 88% during 337 days. Amount of exchanged seawater was 15m³, yielding a calculated productivity of 23kg fish per cubic meter of seawater used. The experiment was continued to day 533 with 1127 fish of 562g initial average body weight. The average body weight at the end was 851g and survival rate from 337 to 533 days was 71%.
Ammonia-nitrogen concentration within the culture system fluctuated throughout the experiment, especially day 100 to 350, sometimes exceeding 5 mg-N/l. A similar trend was seen in the nitritenitrogen concentration with a peak of 4 mg-N/l. The nitrate concentration decreased during day 220 to 350, even though the system was not equipped with a denitrification unit.