Stress in the neighborhood: Tissue glucocorticoids relative to stream quality for five species of fish

Anthropogenic alterations to terrestrial habitat (e.g., urbanization, deforestation, agriculture) can have a variety of negative effects on watercourses that flow through disturbed landscapes. Currently, the relationship between stream habitat quality and fish condition remains poorly understood. The use of physiological metrics such as glucocorticoids (GCs) provides a useful tool for quantifying these effects by relating the health of resident fishes to stream quality. To date, however, most studies that measure GC levels tend to focus on a single, large-bodied species, rather than evaluating how GCs may be influenced differently between species in a community. In this study, we measured cortisol, the glucocorticoid found in fishes, from fish tissues to quantify effects of habitat degradation on the glucocorticoid function of five species of juvenile and small-bodied stream fish which differ ecologically and phylogenetically. Largemouth bass Micropterus salmoides, brown bullhead Ameiurus nebulosus, white sucker Catostomus commersonii, pumpkinseed Lepomis gibbosus, and logperch Percina caprodes were sampled from a reference and a degraded stream. Upon capture, fish were either euthanized immediately, to quantify baseline stress parameters, or following a standardized stressor, to quantify GC responsiveness. As a result of stream degradation largemouth bass possessed altered baseline GC concentrations and brown bullhead and logperch had altered GC responses to a stressor. White sucker and pumpkinseed did not demonstrate any alteration in baseline or post-stress GC concentrations. Together, our results show that different species residing in identical habitats can demonstrate a variety of responses to environmental stress, highlighting the variation in physiological ability to cope under poor environmental conditions, as well as the difficulty of predicting GC dynamics in wild animals. Understanding the relationships between GC function, habitat quality, and population-level processes will increase the ability of researchers and managers to predict how fish communities and aquatic ecosystems will be shaped by anthropogenic environmental change.