Assessment of Altered Rearing Environments on Survival and Performance of Hatchery-Reared Trout: Conservation Hatchery Implications for Cutthroat Trout Used in Reintroduction Programs

Fish reared in conventional hatchery environments may develop behavioral, morphological, and physiological features maladapted for survival and performance in the wild.  To address this problem, conservation hatcheries employ a variety of techniques to improve outplant survival and fitness.  This strategy is commonly used to aid recovery of anadromous salmonid species but has not been applied to artificial propagation of non-anadromous salmonids.  Our objective was to test if different hatchery rearing environments could improve the survival and performance of westslope cutthroat trout used in reintroduction programs.  In 60 day hatchery trials, we compared the survival, growth, and morphology of a slightly domesticated stock of westslope cutthroat trout to a highly domesticated stock of rainbow trout reared in either ‘conventional’ (no cover, hand-fed) or ‘enriched’ (overhead and submerged cover; remote, constant food delivery) environments.  Survival and growth of westslope cutthroat was similar among rearing treatments; however, fish reared in enriched environments exhibited significantly lower aggression,  higher fin condition (a measure of overall fish health) and improved cover seeking behavior (a measure of predator avoidance) (P < 0.05).  The response of rainbow trout to the hatchery alterations was similar to that of cutthroat trout, suggesting that rearing environment affects performance more than degree of domestication.  In 60 day outplanting trials in small ponds, hatchery rearing environment did not have a strong effect on survival of westslope cutthroat trout. However, fish from the enriched treatment lost about half as much fat content and exhibited higher growth rates than the other treatments throughout the outplant phase.  Study results indicated that relatively simple changes in the hatchery rearing environment could lead to marked improvements in survival and performance potential of native trout after stocking.