Shape characteristics of suspended solids and implications in different salmonid aquaculture production systems

In the interests of optimizing the performance and welfare of fish in aquaculture systems and informing simulated and real-world fish farm operations, the particles in two recirculating (RAS), two semi-recirculating (sRAS) and two flow-through systems (FTS) were analyzed using non-invasive digital image techniques to determine shape factors including equivalent circular area diameter (ECAD), circularity, ellipticity and feret diameter. With the exception of feret diameter, most particle shape parameters showed little variation between systems: the majority of particles had a flake-like structure, while round or elongated particles were relatively rare. The exception was one system which yielded large numbers of elongated particles, most probably originating from intrinsic algae production. Generally, mean circularity and ellipticity of particles was about 0.5 and 0.7 respectively, indicating an ellipsoidal rather than spherical shape. Thus, in a departure from previous approaches, it was asserted that calculations based on an ellipsoidal shape will produce more accurate results than those making an assumption of sphericity, when calculating particle volume and surface area. This result has implications for system design and for theoretical calculations. Mechanical treatment did not appear to exert relevant effects on particle shape, apart from expected reductions in feret width and length. Overall, the present results indicate that particle shape is primarily governed by feed composition and intrinsic biology rather than by production system type. Moreover, an assumption of ellipsoidal shape presents a robust modelling approach for further scientific calculations.