The glucocorticoid stress response is repeatable between years in a wild teleost fish

Patterns of glucocorticoid (GC) hormone regulation exhibit considerable inter-individual variation that is often examined relative to individual traits and fitness measures. Although stress-induced GC concentrations are repeatable within an individual in captive populations, this assumption remains untested in wild animals in their natural environment across longer time periods. We assessed the repeatability of baseline and post-stress GC concentrations in a wild teleost fish. Largemouth bass (Micropterus salmoides) were captured and subjected to a standard stress protocol and then stocked into a small research lake. Upon recapture by angling up to 1 year later (n = 26), fish were re-sampled following identical methods. After controlling for a strong effect of water temperature, we confirmed repeatability of post-stress cortisol concentrations despite stress presumed to accompany relocation. We documented no consistency in baseline GC concentrations. This study serves as an important validation for the use of post-stress cortisol concentrations as an individual trait. However, the effect size of repeatability was lower than that found in other taxa. Results also bring forth the reality that environmental variables such as temperature must be considered in studies where these factors can vary, such as when sampling wild animals at liberty.