ABSTRACT

Corticosterone is the primary glucocorticoid hormone produced by reptiles in response to stressful stimuli. Evaluating hormone responses to stress in reptiles relies on acquiring baseline corticosterone levels; however, the stress associated with restraint needed to collect blood samples from animals can affect the results. Therefore, it is important to obtain a blood sample in a relatively short time after the capture of an animal. In some avian and reptilian species, a “3 min rule” has been determined, suggesting that blood samples collected within 3 min of capture are more likely to represent baseline corticosterone levels. The purpose of this study was to determine a time limit for collection of blood samples to evaluate baseline corticosterone concentrations in captive gopher tortoises, Gopherus polyphemus. Four nonreleasable, adult gopher tortoises were used for this study. All tortoises were acclimated to their captive environment for 10 months. Each tortoise was then manually restrained for a continuous 60 min. Blood samples (0.5 ml) were collected from the subcarapacial venous sinus at 0, 2, 4, 6, 10, 30, and 60 min. Each tortoise was sampled during a separate 24 h period. After a 4 wk washout period, all tortoises were sampled a second time as described above, except that a volume of 1.0 ml of blood was collected at each time point. The additional 0.5 ml of blood was used to determine a complete blood count (CBC) for each sample. Plasma corticosterone concentrations were determined by quantitative radioimmunoassay. Corticosterone data were analyzed for a time at which a significant increase from time 0 occurred. The CBC data were also analyzed for significant changes associated with time. Corticosterone concentrations were found to increase significantly at 30 and 60 min, although levels began to increase after 6 min of restraint. No significant changes in CBC parameters were found. Based on this study, it is recommended that blood samples for baseline corticosterone concentrations be collected within six minutes of capture for gopher tortoises.