Chronic stress causes cortisol, cortisone and DHEA elevations in scales but not serum in rainbow trout

Fish scales have been reported to incorporate cortisol over long periods of time and thus provide a promising means of assessing long-term stress in many species of teleost fish. However, the quantification of other stress related hormones has only been accomplished in our previous study conducted in goldfish (Carassius auratus). DHEA is a precursory androgen with anti-stress effects used alongside cortisol to diagnose chronic stress via the cortisol:DHEA ratio in mammals. Included in DHEA's anti-stress mechanisms are changes in the metabolism of cortisol to its inactive metabolite cortisone suggesting the relationships between cortisol, DHEA and cortisone may be additionally informative in the assessment of long-term stress. Therefore, to further explore these con-cepts in a native fish species and generate more comprehensive comparisons between scale and serum hormone concentrations than was possible in our previous study we implemented a 14-day stress protocol in adult rainbow trout (Oncorhynchus mykiss) and quantified resulting scale and serum cortisol, cortisone and DHEA concentra-tions. As predicted, elevations in scale concentrations of all hormones were observed in stressed trout compared to controls but were not reflected in serum samples. Significant differences in the cortisol:DHEA and cortisone: cortisol ratios were also found between control and stressed group scales but not serum. These results suggest not only that scales provide a superior medium for the assessment of long-term stress but also that the addition of scale cortisone and DHEA may provide additional relevant information for such assessments.

Automated summary

Fish scales can incorporate cortisol over long periods of time, making them a promising tool for assessing long-term stress in teleost fish. This study aimed to further explore the relationship between cortisol, DHEA, and cortisone in a native fish species by implementing a stress protocol in adult rainbow trout. The results showed that scale concentrations of all hormones were elevated in stressed trout compared to controls, suggesting that scales provide a superior medium for assessing long-term stress. Additionally, the cortisol:DHEA and cortisone:cortisol ratios were different between control and stressed group scales, indicating that the addition of scale cortisone and DHEA may provide additional relevant information for such assessments.