Using rainbow trout Oncorhynchus mykiss as self-feeding actuators for white-spotted charr Salvelinus leucomaenis: Implications for production and welfare

Self-feeding systems, where fish actuate a trigger to obtain food, can be a useful feed management tool for aquaculture. However, some species such as the white-spotted charr Salvelinus leucomaenis can be poor self-feeders. The current experiment evaluated the production and welfare effects of growing a single competent self-feeding ‘demonstrator’ species, rainbow trout Oncorhynchus mykiss, in tandem with groups of inexperienced, ‘observer’ white-spotted charr. During Part I (PI, 50 days), all demonstrator groups (n = 4) utilised the self-feeders from day one, whilst no naïve charr successfully actuated the self-feeders. This enhanced utilisation had a significant and positive effect upon the growth and condition of observer charr. When demonstrator trout were removed during Part II (PII, 26 days), only one group of observer and one group of naïve charr started actuating the trigger, on the 1st and 21st day of PII, respectively. This resulted in poor growth performance in both observers and naïve charr, and there were no significant differences between treatments. However, observer fish still retained a significantly better condition factor than naïve fish at the end of PII. There were no significant differences in the levels of fin erosion, opercular erosion and mortality between observer and naïve charr throughout the experiment.This study confirms the previous assumption that white-spotted charr are poor self-feeders, but their production performance and welfare can be improved by growing charr in tandem with experienced and proficient self-feeding rainbow trout.