Effects of capture and recovery on plasma levels of cortisol, lactate and gonadal steroids in a natural population of rainbow trout

Rainbow trout were captured by angling from a run of spawning fish on the Tongariro River in northern New Zealand, to examine the effects of catch and release angling on stress and reproductive parameters. Fish were blood sampled immediately after capture at playing times of <5 or 15 min, or after 1 or 24 h of recovery in stream enclosures. Plasma samples were assayed for cortisol (F), lactate, testosterone (T), 17β‐oestradiol (E 2 ), and 17a,20β‐dihydroxy‐4‐pregnen‐3‐one (17,20βP). Plasma F levels were similar to those of hatchery stocks of rainbow trout, at capture, and became significantly elevated 1 h after capture. Plasma F was still clevated in some fish 24 h after capture. Plasma lactate levels began to increase 15 min after capture, were further elevated 1 h after capture, and had returned to normal 24 h after capture. We proposed that metabolic recovery had occurred but that some animals were still experiencing some degree of stress, possibly in response to holding conditions in the river. Both plasma T and E 2 were depressed 24 h after capture, whereas there was no change in plasma 17,20βP. This is consistent with other findings showing that acute stress is associated with depression of plasma levels of T and E 2 . There was no mortality as a result of capture or any of the handling protocols. We conclude that catch and release angling will result in negligible mortality, but may have an inhibitory effect on some reproductive processes.