Spreading of feed pellets in a sea cage for salmon farming using an automatic rotor spreader feeding system.A CREATE project

Summary

Efficient production of fish in large cage units demands a feeding practice which is according to the fish’s behavioral and physiological requirements. It is generally presumed that spreading the feed pellets uniformly over a large pen surface area improves feed intake. Pneumatic feeding systems are commonly used to spread feed pellets in the cages, however, pellet degradation increases with increasing airspeed. The aim of this study was to describe the surface distribution of feed pellets in sea cages when using a pneumatic feeding system with a rotor spreader. Feeds with three different pellet sizes were used and two different spreader types were tested, both with different orientation of the top unit. The spreader test was carried out with three different airspeeds of the feeding system. The test was carried out in an outdoors square steel cage (24 x 24 meter) with the rotor spreader positioned in the centre of the cage. Styrofoam boxes were used to collect the pellets. The boxes were positioned in a row on each side of the spreader, referred to as two opposite directions. The results showed that the pellets were distributed unevenly over the cage surface. One direction had higher spatial pellet densities and less area covered with feed pellets. The opposite direction showed a more dispersed pattern and longer spreading distance. Between 18.2 % and 79.8 % of the cage surface was covered with feed pellets and spatial pellet densities between 0 g m-2 and > 200 g m-2 were measured depending on spreader, tilting of the top unit and airspeed. Increasing airspeed gave a longer spreading distance of pellets, measured from the centre. The effect of airspeed was more pronounced for spreader direction with dispersed spreading. Also, with increasing airspeeds the areas with high spatial pellet densities were decreased for both directions, indicating a more uniform spreading with higher airspeeds. The pellet distribution for the different pellet sizes was similar. Spreader type and tilting significantly affected pellet distribution. In conclusion, this experiment showed that when using a pneumatic feeding system, distribution of feed pellets was non-uniform over the cage surface and that spreading area could be manipulated by airspeed, spreader type and tilting position, while the spreading pattern was similar for feeds of different pellet sizes.