Translocation efforts often use captive-reared animals to help bolster or re-establish wild populations. However, captive environments are highly dissimilar from wild conditions and usually deprive animals of experiences that promote behavioral, physiological, and morphologic development. Captive rearing and translocation efforts are underway for eastern hellbenders (Cryptobranchus alleganiensis alleganiensis); yet, hellbenders reared in aquaria that lack stimuli are ill-prepared for riverine environments and often make long-distance downstream movements following release. We altered standard captive techniques and reared juvenile hellbenders with and without water current for eighteen months. We quantified morphological plasticity and swim performance as a function of rearing environment.
Conditioned hellbenders gained weight more slowly compared to unconditioned individuals, which we assert is a result of greater energy expenditure against moving water. Moreover, we detected evidence for phenotypic plasticity as conditioned individuals developed more shallow tails by the end of the rearing period. We did not find morphologic plasticity to influenence hellbenders’ swimming ability; however, we did find that after three swim trials, conditioned hellbenders were less likely to need manual motivation and more likely to successfully complete the trial. Moreover, conditioned hellbenders tended to improve through time and decreased the number of upstream attempts at each trial. Together, our data suggest that the addition of water current to hellbender rearing environments induces a more streamlined tail and improves hellbenders’ ability to reach upstream refugia. We advocate incorporating natural conditions into captive rearing programs to better prepare animals for and potentially improve the success of future translocations.