The experiment was conducted in fiberglass tanks located inside a temperature-controlled concrete hatchery building. Four independent recirculating system units were used. Each unit comprised of five 0.43 m3 (1.0×1.0×0.43 m, L×W×D) fish
rearing tanks and one (0.43 m3) biological filter tank (Fig. 1). The water volume was 0.3 m3 per tank. The following filter media were tested (Fig. 2).