The higher recovery of HNSP compared to LNSP feces by sedimentation is consistent with the results of a previous study using the same feeds in RAS (Meriac et al., 2014). However, it is important to acknowledge that the feces used in the sonication experiments apparently represented only 68% and 49% of the total feces produced with HNSP and LNSP diets, respectively. Thus, we have to assume that the composition of the collected feces was representative for the total feces produced by the fish. According Wong and Piedrahita (2000), the up flow velocity of 0.23 cm/s in our settling units should have been sufficient to collect at least 87% of all settleable solids.