The effects of exercise on behavior and reproductive success of captively reared steelhead

Steel head Oncorhynchus mykiss collected as eyed eggs from the Hamma Hamma River, Washington, and reared in high (similar to 1 body length/s) or low current velocity (similar to 0.25 body lengths/s) were tested for differences in reproductive behavior in both an experimental spawning channel and their natal river. We conducted continuous (24-h/d) behavioral observations in the spawning channel and applied DNA pedigree analyses to explain the variation in individual reproductive success. Female steelhead reared in high and low current velocities did not exhibit differences in reproductive behavior in the spawning channel, but females reared in low current velocity were snore frequently observed constructing nests in the Hamma Hamma River. Males reared in low-velocity tanks were more frequently observed courting females in the spawning channel and in the river. A pedigree analysis revealed no significant differences in reproductive success between the rearing treatments. Male reproductive success in the spawning channel was significantly correlated (r(2) = 0.602; P < 0.001) and the dominant male was identified by the frequency of spawning in both treatments. There was no apparent effect of male or female body mass on breeding behavior or reproductive success in the spawning channel. All 24 females and 23 out of 24 males produced free-swimming offspring in a 5.5% subsample of the fry population. This study suggests that releasing captively reared steelhead reared under conventional (i.e., low current velocity) culture conditions should be considered (along with other options) as a potentially viable component of captive rearing and breeding programs.