Limited Effects of Temperature on Captive Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis) Growth.

Amphibians are among the most threatened vertebrates, with 41% of species at risk of extinction due to factors such as habitat loss, pollution, and climate change. One such species, the Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis), has experienced significant population declines, particularly in Indiana. Conservation efforts, including captive breeding and rearing, have been initiated to mitigate these losses. However, the rearing conditions that optimize the growth of this species in captivity are understudied. Higher temperatures are known to increase amphibian growth, but many captive rearing facilities rear Eastern Hellbenders at relatively low temperatures (e.g., 16°C). Our goal was to assess the effects of rearing temperature on Eastern Hellbender growth under captive rearing conditions. Eastern Hellbenders (N = 207) were reared at two temperatures (16°C and 21°C) at the Indianapolis Zoo. Every 8 weeks from February 2023 to July 2024, we collected mass and total body length on each individual to assess changes over time. Contrary to predictions, we found no evidence that higher temperatures increased the growth (mass or total length) of Eastern Hellbenders. This suggests that Eastern Hellbender growth is unlikely to be influenced by the rearing temperatures used at most captive facilities. These results challenge assumptions about the role of temperature in captive rearing outcomes and suggest that future research focus on other variables (e.g., diet, density) that might enhance captive-rearing efficiency.