The Use of Fish Scale Hormone Concentrations as a Non-Lethal Biomonitoring Tool in Teleost Fishes
Teleost fish serve as an essential resource to the human population and thus their conservation is of extreme importance. In an effort to monitor the effects of anthropogenic activity in fishes, the quantification of cortisol as an indicator of increased stress is often employed. Cortisol is a glucocorticoid released by the hypothalamic-pituitary-inter-renal (HPI) axis in fishes in response to a stressor. Cortisol alongside other stress hormones then serves to equip the fish with the resources required to overcome the stressor. However, if this response is repeatedly engaged the state of stress can change from acute to chronic often resulting in adverse effects. Fish scales are durable calcified structures that can be sampled non-lethally from many fish species. Recently the fish scale has been shown to incorporate and store cortisol for long periods of time allowing it to serve as a medium for long-term stress assessments. This has now been accomplished in eight species of fish and recent studies have provided promising evidence for the use of fish scale cortisol concentration in the evaluation of a variety of chronic stressors. However, cortisol quantification alone is limited in its ability to diagnose chronic stress and thus my thesis research sought to investigate additional stress related hormones within the scale. The first two experiments quantified scale cortisol, cortisone and DHEA after a 14-day randomized stress protocol. In goldfish this resulted in significantly elevated circulating cortisol and cortisone and while these hormones were only somewhat elevated in the scales the scale cortisol:DHEA ratio was significantly elevated in stressed goldfish. By contrast, the same stress protocol significantly elevated scale but not serum concentrations of all three hormones in rainbow trout in the second experiment. The third experiment included cortisol, progesterone, testosterone and 11-ketotestosterone to allow for the evaluation of both chronic stress and associated effects on reproduction. Artificial elevation of cortisol, progesterone and testosterone using coconut oil implants produced many interactions both among different hormones and among the two sample media: serum and scale. It was found that injected progesterone and testosterone were converted to 11-ketotestosterone, the primary androgen in teleost fishes and that well-studied negative interactions between cortisol and androgens are also relevant to scale hormone analyses. While the roles and relationships between the hormones explored in these experiments as well as their partitioning from blood to scale still requires further investigation, fish scale hormone concentrations appear to provide a unique and useful tool for future biomonitoring efforts.
biomonitoring, conservation physiology, glucocorticoid, physiological stress, scale, steroid hormone
Master of Science (M.Sc.)