Growing amago and rainbow trout in duoculture with self-feeding systems: Implications for production and welfare

Abstract

Some salmonids such as rainbow trout ( Oncorhynchus mykiss: Walbaum, 1792) can quickly learn to use self-feeding systems while others such as amago ( Oncorhynchus masou masou: Brevoort, 1856) can take longer. The current study examined the potential costs and benefits of growing each of these species in duoculture with self-feeding systems in terms of welfare and production. Three self-feeding treatments were evaluated: rainbow trout in monoculture (RM), amago in monoculture (AM), and rainbow trout and amago in duoculture (D). Self-feeder learning time for all RM and D groups varied from 1 to 9 days, while AM ranged from 2 to 25 days. Within the D treatment there was no indication that amago learned to use self-feeders by watching the rainbow trout. Initial food intake was significantly lower for AM than the other groups, but this did not result in significantly lower growth rates. Further, the growth performance of both amago and rainbow trout were similar, irrespective of being grown in either mono- or duoculture. There were no significant differences in feed wastage between treatments and feed wastage was < 6%. The welfare implications of duoculture for each species were quantified using four welfare indicators: aggression, fin damage, condition factor and mortality. No significant differences were found in any of these indices. The results of this study suggest that when using duoculture for growing rainbow trout and amago with self-feeding systems, amago benefits from reduced variability in self-feeder learning times, i.e. all duoculture groups learned within 5 days while amago-only groups took up to 25 days to learn. Further to this, there were no obvious detrimental effects upon production and welfare.