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654 MESA AND SCHRECK 150 •-• multiple electroshock J a ?- -single electroshock E 125 •-• 30 s handling & o• • • • c control J 100 d O t V) F- 5 a ?a r 0 50 b 1 i U) 25 1 ?b J bf c b ------ Aab (L 0 v 60 0 ---T- o e- 0 1 3 6 12 24 168 TIME (h) FIGURE 7.-Mean plasma cortisol concentrations in Cedar Creek Hatchery cutthroat trout subjected to a single 8-s, 500-V-DC electroshock; three 8-s, 500-V-DC electroshocks separated by 0.5 h; or a 30-s handling stress relative to unstressed controls. Means represent data from two trials combined (except for fish subjected to handling stress). Means (N = 10) within a time interval with no letters in common are significantly different (P < 0.05); time intervals with no letters shown indicate no significant difference among the means. Vertical bars represent 1 SE. for wild cutthroat trout. However, the patterns of recovery from stress were different. In the artificial stream, normal behavior patterns, aside from a decrease in aggression, returned by 24 h after treatment. At Mill Creek, it was often difficult to even locate marked fish 24 h after they were shocked and marked. This discrepancy in recov- ery patterns between fish in the two systems is most likely due to the much more complex en- vironment of the natural stream, which would make it more difficult for us to locate and observe marked fish. Wild cutthroat trout appeared to be more se- verely affected by the stresses resulting from cap- ture and marking than hatchery fish in our arti- ficial stream. Various investigators have com- pared the ability of hatchery and wild rainbow trout Oncorhynchus mykiss to respond to various stresses (Wydoski et al. 1976; Casillas and Smith 1977; Woodward and Strange 1987), but results have been equivocal. Although we found that both wild and hatchery cutthroat trout decreased their activity upon release, hatchery fish generally re- covered in about 1-2 h, whereas wild fish required at least 24 h. Wild fish showed a general lethargy that was evident primarily as a marked decrease in aggressive behavior. Although there was ample opportunity for aggression to occur throughout the day after treatment, it never consistently returned to pretreatment rates. When aggression did occur, it was less intense. The relative absence of overt agonistic behavior throughout the posttreatment observation period suggests that normal behavior patterns were altered even though the fish were feeding. However, for at least the first 4 h after the fish were shocked and marked, most fed slug- gishly and did not swim far to acquire food. Feed- ing intensity increased later in the day and also at 24 h, presumably after the effects of the stress had decreased. The effects of electroshocking and marking on the integrity of a dominance hierarchy may affect the accuracy of population size estimates. Among wild fish, intermediate and subordinate fish may require more time for recovery from stress than social dominants. Hatchery fish, regardless of rank, may be more resilient after exposure to experi- mental stresses. The hypothesis that there is an inverse relation between dominance status and a low-level, chronic state of stress in fish (i.e., that dominant fish are under the least stress) has been inferred by several investigators (Erickson 1967; Noakes and Leatherland 1977; Ejike and Schreck 1980) and is consistent with our results for wild fish. Whether this apparent differential ability to respond to stress would have any effect on esti- mating population size is speculative, but such effects might be related to the proportions of dif- ferently ranked individuals residing in the stream section. Our inability to observe much behavioral change in fish during multiple-electroshock experiments at Mill Creek does not lead to the conclusion that multiple electroshocks have no effect. Although