At high accumulation RAS (30 l/kg feed/d) water flows frows from 4 culture ranks (0.450m), 9 experimental tanks (0.060 m)-drum filter(Hydrotech HDF 501-1p,0.02 m,mesh size 90 um)-sump1(0.600m)-denitrifying reactor(0.480m)-trickling filter (0.070m, water flow 151.2 l/min; ventilator air flow: 1.39m/s; media Bionet 200m/m,media volume 1.200m)-sump2 (0.300m)-oxygen cone(0.050m)-experimental tanks.