Effects of Different Water Velocities on the Hatchery Rearing Performance and Recovery from Transportation of Rainbow Trout Fed Two Different Rations

Abstract

AbstractWe examined the effects of exercise on hatchery rearing performance and posttransportation stress recovery, growth, and survival of Rainbow Trout Oncorhynchus mykiss reared for 9 weeks in one of three water velocities (0.5, 1.5, or 3.0 body lengths (BL)/s) and fed either a restricted ration or to satiation. The influence of previous exercise regimes on survival, growth, and stress recovery for 8 weeks after transportation of the fish fed a restricted ration was also evaluated. During hatchery rearing, reduced growth and poorer food conversion ratios at higher velocities (1.5 and 3.0 BL/s) were only observed in restricted ration‐fed fish, with satiation‐fed fish exhibiting no differences in hatchery rearing performance among the water velocities. Condition factor changed with exercise regime and was significantly greater in restricted ration‐fed fish at 3.0 BL/s and satiation‐fed fish at 1.5 and 3.0 BL/s. Hepatosomatic index was unaffected by exercise but was significantly greater in the fish fed to satiation, whereas the viscerosomatic index was not significantly affected by either exercise or ration. Hematocrit was also unaffected by exercise but was significantly lower in fish fed to satiation. Cortisol levels after 9 weeks of hatchery rearing were the same for all exercise regimes regardless of feed ration. Cortisol levels after transportation were also the same for all exercise regimes and cortisol levels returned to pretransportation levels within 24 h. Growth and survival after transportation were the same for all fish regardless of their previous exercise regime. These results indicate that that fish can be reared using adequate velocity to maintain the self‐cleaning properties of hatchery tanks without fear of negatively affecting fish condition or posttransportation performance, although exercise should be paired with adequate food intake to avoid decreased hatchery growth and elevated food conversion ratios.