Factors determining the size of suspended solids in a flow-through fish farm

The efficiency of the mechanical effluent treatment in flow-through fish farms depends mainly on the size distribution of the suspended solids. We measured the particle size distribution (PSD) throughout a commercial flow-through trout farm using a high-resolution laser technique. This resulted in a space-resolved data set that allows us to identify fish density, fish contact surface area, and distance from inlet as general factors controlling PSD. Furthermore, we present evidence that turbulence generated by aeration units and fish-feeding activity also induces particle breakdown. Contrary to the common perception, however, the size of suspended particles increases rather than decreases as they progress through the farm. The waterfall at the end of the fish farm significantly reduced the size of the suspended solids and hence the efficiency of the drum filter installed behind it. It was calculated that removing the waterfall would increase the effectiveness of the drum filter by about 33%. Based on these findings we give advice on aquaculture facility design and management that will help to maintain or even increase the size of suspended solids. (C) 2004 Elsevier B.V. All rights reserved.