Feed pellet distribution in a sea cage using pneumatic feeding system with rotor spreader

In modern salmon farming feed is commonly transported to the cages and distributed over the surface by means of a pneumatic conveying system. Airspeed in the feeding system is used to spread the feed, although high airspeed causes pellet breakage. Thus, knowledge about how airspeed affects spreading of feeds of different pellet sizes is necessary in order to optimise the feeding routines at salmon farms.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 orientations 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 m × 24 m) 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. Depending on airspeed, spreader and tilting of the top unit, between 18% and 80% 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. 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.

► Pellet distribution from a pneumatic feeding system is described.
► Pellet size, air speed, spreader type and orientation of spreader were tested.
► Feed distribution over the cage surface was non-uniform.
► Between 18% and 80% of the cage surface was covered with feed pellets.