Studies on the improvement of self-feeding system to fasten feeding for cultured fish.

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Two of the primary aims of self-feeding are to maximize growth and minimize food wastage. Earlier work has reported that the self-feeding trigger (which controls food delivery) can be monopolised by a few individuals, whose appetite may not reflect the needs of the whole group. We hypothesized that these problems may be circumvented if we combined the self-feeding systems of different groups of fish.Eighteen groups of rainbow trout (n = 10 group^<-1>) were allowed independent access to self-feeders for 14-28 days. When the self-feeding systems were paired between tanks (n = 9 pairs, for a total of 12-24 days) there was no detrimental effect on overall group ration. Interestingly, in 5 cases, one group from each pair decreased or ceased actuating the trigger, and became dependent on the trigger actuations of its paired 'satellite' group for food delivery (although this did not lead to a reduction in daily group ration). When the combination self-feeding was terminated and independent access to the feeders resumed, 75% of groups attained the pre-combination ration level almost immediately, with the remaining groups reaching the level within 10 days.In the final year of the study (H15), we scaled-up the initial experiment by using larger groups (50 trout per group) and bigger tanks. Due to infection problems and associated mortalities, we had to suspend the Grant-in-Aid until disease problems were brought under control. When experiments were resumed, we compared ration, growth, and food wastage of the combined self-feeding regime versus an independent self-feeding regime. Groups under the combined self-feeding regime consumed significantly more food and exhibited significantly better growth than groups under the independent self-feeding regime. Food wastage was low (< 1%) irrespective of feeding regime. These results suggest that the combined self-feeding regime is a successful method for feeding large groups of fish.