3. Waste production
3.1. Feed conversion in RAS
Although liable to imprecision due to large differences in operational parameters, it might be concluded that feed utilization by fish cultured in RAS often compares favorably to that of fish raised in other type of culture systems (Table 1). Production of waste in RAS, like in any other aquaculture system, depends on a number of factors with as most important ones: (a) the type and age of fish, (b) the feed composition, (c) the feeding regime, and (d) the prevalent water quality conditions in the system. In RAS, high feed utilization efficiencies can be attained by controlling some of these factors. For instance, feeding in RAS, whether performed manually
or automatically, is well monitored. Hence, lapses of off-feed are easily identified thus minimizing overfeeding and consequent accumulation of uneaten feed in the system. In addition, batch wise growth of uniform size classes of fish further contributes to an efficient feed utilization in RAS (Karipoglou and Nathanailides, 2009). Another factor contributing to reduced feed wastage in RAS is water quality control. Treatment systems in RAS are designed to control water temperature and critical water quality parameters within an acceptable range hence avoiding inferior water quality conditions and concomitant reduced feed utilization efficiency.
Finally, in these relatively well monitored systems, a quick response to changes in water quality conditions may also contribute to an efficient feed utilization (Martins et al., 2010).