DHEA and Cortisol in Rainbow Trout (Oncorhynchus mykiss): Effect of Sex, Sexual Maturity, and Acute Stress Exposure

Glucocorticoids like cortisol are widely used to assess stress in fish, but their interpretation can be limited. Incorporating dehydroepiandrosterone (DHEA), a hormone with anti-glucocorticoid and neuroprotective effects, may provide a broader understanding of hypothalamic-pituitary-inter-renal (HPI) axis activity. As DHEA data in fish remain scarce, this study examined its role in rainbow trout (<i>Oncorhynchus mykiss</i>) subjected to acute stress (30 min confinement), considering sex and sexual maturity. Cortisol and DHEA were quantified by optimized radioimmunoassay (RIA) in serum, muscle, fin, and scales, and gonadal histology was performed to confirm reproductive status. Both hormones were successfully measured in all matrices, with serum DHEA levels notably higher than those reported to date in fish. As expected, serum cortisol increased markedly after stress and correlated with levels in muscle and fin but not in scales, which appears to reflect chronic rather than acute exposure. In contrast, serum DHEA showed no stress-induced changes and only minor sex- and maturity-related differences, although alternative matrices displayed variable patterns, particularly in muscle and fin. The cortisol/DHEA ratio in serum mirrored cortisol dynamics, suggesting limited utility for acute stress assessment, while tissue-specific DHEA variation may integrate longer-term influences. Further research is needed to clarify the role of DHEA under chronic stress and its potential origins in inter-renal tissue, gonads, or the brain.