The aquaculture live feed organisms Acartia tonsa (a calanoid copepod, experiment 1) and Brachionus Cayman (a rotifer, experiment 2) were cultivated in marine recirculating aquaculture systems (RAS), respectively. The pilot plant was built as a combination of conventional RAS (cRAS) and as a modified RAS which implemented an ultrafiltration membrane bioreactor (MBR) for the removal of fine suspended solids and colloidal particles as part of the treatment system (mRAS). The two treatment schemes were connected to the same biofilter (a moving bed bioreactor). In the first experiment, the membrane was operated with no extraction of concentrate, and hydraulic retention time (HRT) of 6 hours (i.e., water exchange in the cultivation tanks of 4 times per day). In the second experiment, the membrane was operated with daily extraction of concentrate, and HRT of 12 hours. Results show that the MBR option is more efficient in removing particles from the recycle stream than conventional RAS. However, the impact this has on the number of particles in the live feed cultivation tanks is not readily apparent based on particle analysis. The amount of suspended solids added during feeding exceeds the amount removed in the recycle system. This requires a higher recirculation rate and different membrane operating conditions.