Performance and Behavior of Rainbow Trout Reared in Covered Raceways

Abstract

Rainbow trout (Oncorhynchus mykiss) were reared in outdoor concrete raceways either with or without plywood covers. Growth, feed conversion, and mortality were not significantly different between the two groups after 215 d. Autopsy-based health and condition variables were not significantly different between the two groups. Fin length measurements were also not significantly different, indicating no reduction in fin erosion due to rearing in covered raceways. Fin erosion was worst at the end of the study (mean fin indexes, 1.45 and 1.60), but signs of fin erosion also occurred in the first autopsy sample when the fish were about 10 g each (mean fin indexes, 0.8 and 1.0). In an outdoor observation tank, single fish were observed for 5 min. Preference for the covered end of the tank was evident among fish from both covered and uncovered raceways (P < 0.001) and did not differ between treatments. Observations were also made for four-fish groups over a 45-min period either in the presence of a stuffed eagle or without it. During the first 15 min, fish from covered raceways stayed under cover more frequently than fish from uncovered raceways when the eagle was present. No significant differences in cover preference between fish from cover or no-cover treatments were noted during the second and third 15-min periods or when all periods were pooled. There was a tendency for all groups to seek cover less frequently in each successive time period.