Aquaculture Europe 2023

September 18 - 21, 2023


Add To Calendar 19/09/2023 16:15:0019/09/2023 16:30:00Europe/ViennaAquaculture Europe 2023INFLUENCE OF STRESS, SEX AND SEXUAL MATURITY ON SCALE CORTISOL AND DHEA CONCENTRATIONS IN RAINBOW TROUT Oncorhynchus mykissStrauss 3The European Aquaculture Societywebmaster@aquaeas.orgfalseDD/MM/YYYYaaVZHLXMfzTRLzDrHmAi181982


M. Bortoletti*, A. Meloni, E. Fonsatti,  G. Gabai , G. Radaelli and D. Bertotto


Department of Comparative Biomedicine and Food Science, University of Padova , Italy




 Fish welfare is traditionally assessed  by  measuring cortisol levels,  which is  the quintessential stress hormone in these animals. However, the best practice to assess animal welfare is to utilize multiple indicators  in order  to provide a more comprehensive portrait of  the animal condition, especially when assessing long-term stress . Among the physiological indicators, dehydroepiandrosterone (DHEA), a precursory androgen with anti-stress effects, seems to be promising in diagnosing  mammalian chronic stress through the cortisol:DHEA ratio [1] besides DHEA  has recently been demonstrated to increase in fish exposed to a chronic stress [2] . However, while DHEA i n mammals has been shown to act in opposition to cortisol in many physiological pathways and to exhibit antioxidant, neuroprotective and immuno-protective characteristics [3] ,  still very little is known about its physiological meaning  and  possible implication  in the stress response in fish .  For this reason, the present study  aimed  to investigate how the levels of this steroid are affected not only b y  a  common stressful aquaculture practice, but also by sex and degree of sexual maturity in rainbow trout (Oncorhynchus mykiss) scales, a promising medium for multi-h ormone s tress analyses [4].

Materials and methods

 The experiment was performed at a commercial farm where four groups of rainbow trout (n=96 ) were sampled: mature females (990 ± 28.5 g) and males (1005 ± 40.7 g), immature females (1350 ± 48.8 g) and males (1394 ± 33.3 g) . Half fish of each group were subjected to 30 minutes confinement  stress  and the other half were controls. Prior to sampling , fish were sacrificed with an excess of anesthetic (MS222 Sigma-Aldrich) and subsequent cut of the spinal cord. S cales were collected  after removing excess mucus by scraping the side of the fish  with a small plastic rod and subsequently stored at -20°C until the analysis.

 Cortisol  and DHEA were quantified in the scal es using  a specific microtitre radioimmunoassay (RIA). Different washing protocols  were tested and the RIA protocol was adapted and validated. All the data are expressed as mean ± standard error and were previously evaluated for normal distribution. Differences between treatments were analyzed using a general linear model (GLM) using sex , maturity  and stress as main factors.  The level of statistical significance was set at p < 0.05.

Results and discussion

 Among the three factors studied, the degree of sexual maturity  was  the major factor influencing cortisol concentration , with mature fish having significantly higher cortisol levels than the immature (p<0.01) .  This result  aligns  with previous studies conducted on rainbow trout, in which  mature individuals, both males and females, showed higher plasma cortisol levels than immature [5].  Differently, sex affected DHEA concentration, with males showing significantly higher levels than fem ales (p<0.05).  To our knowledge, DHEA has not been previously quantified in relation to sex in fish and thus there is  currently no information available to compare our findings. However, there is evidence of higher DHEA concentrations in males than females both in humans and other mammals  [6,7]. R esults did not show stress-related difference in both cortisol and DHEA levels. T his could be linked to the kind of stress applied in this study , i.e. acute, and to the bony nature of the scales, that slowly accumulate hormones. Nevertheless,  the cortisol:DHEA ratio ,  resulted higher in the stressed fish compared to the controls, although not significantly (p =0.058). At present ,  knowledge about the involvement of DHEA in fish stress response is scarce. However, considering that it has been shown to counteract cortisol in mammals, this ratio might  better describe an animal’s stress status than either hormone alone . Indeed, in humans and other vertebrates, high ratios of cortisol to DHEA have been considered indicative of chronic stress [8] .  Finally, the meaning of the interactions between the three factors studied (sex, maturity and stress) is still under investigation .


 In the present study, both cortisol and DHEA levels were successfully quantified in the scales of rainbow trout. Furthermore, the obtained levels are perfectly in line with those reported in the only other study currently present on rainbow trout exposed to chronic stress [2], attesting the applicability of the RIA method developed in this study in quantifying these hormones in fish scales. T o our knowledge, this is the first time DHEA has been evaluated with respect to sex and degree of sexual maturity in fish.  Nevertheless,  further investigation is required to better understand the role of this hormone in fish physiology. Moreover ,  these results need  to  be implemented  by  assessing a longer-term stress  in order  to test the suitability  of DHEA  as an alternative physiological indicator to be used alongside cortisol in the assessment of chronic stress in fish.


 [1] Whitham et al. (2020). Beyond Glucocorticoids: Integrating Dehydroepiandrosterone (DHEA) into Animal Welfare Research. Animals (Basel), 10, 1381.

 [2]  Kennedy and Janz (2023). Chronic stress causes cortisol, cortisone and DHEA elevations in scales but not serum in rainbow trout. Comp Biochem Physiol A Mol Integr Physiol., 276, 111352.

 [3]  Hu et al. (2000). Anti-stress effects of dehydroepiandrosterone: protection of rats against repeated immobilization stress induced weight loss, glucocorticoid receptor production, and lipid peroxidation. Biochem . Pharmacol, 59, 753–762.

 [4] Kennedy and Janz (2022). First Look into the Use of Fish Scales as a Medium for

Multi-Hormone Stress Analyses. Fishes, 7, 145.

 [5]  Milla at al. (2009) . Corticosteroids: Friends or foes of teleost fish reproduction? Comp Biochem Physiol A Mol Integr Physiol. , 153 , 242-251.

[6] Goldman and Glei (2007) . Sex differences in the relationship between DHEAS and health. Exp Gerontol. , 42 , 979-87 .

[7] Tagliaferro and Ronan (2001). Physiological levels and action of dehydroepiandrosterone in Yucatan miniature swine .  Am J Physiol Regul Integr Comp Physiol. , 281, R1-R9.

[8] Sollberger and Ehlert (2016).  How to use and interpret hormone ratios. Psychoneuroendocrinology, 63, 385–397.