Resting egg formation of the rotifer Brachionus plicatilis using a semi-continuous culture method

This study examined whether the efficiency of resting egg production of the marine rotifer Brachionus plicatilis is improved by employing the semi-continuous culture method. Rotifers were cultured in 0.5 m(3) polycarbonate tanks for 17-23 days by feeding frozen and concentrated Nannochloropsis oculata. An average harvest of 9.0 x 10(4) resting eggs per a gram (dry weight) N. oculata was achieved, which was 2.5 times more efficient than that from batch cultures. Although the water quality was comparatively improved (less concentrations of NH4-N, NH3-N and DON) in semicontinuous rotifer cultures, two out of four cultures collapsed on 15-20th days, probably due to the bacterial effect. The semi-continuous cultures were stabilized by placement of a nylon filter to remove particulate organic materials. With a filter, 1.3 times more resting eggs were harvested on average.