First Look into the Use of Fish Scales as a Medium for Multi-Hormone Stress Analyses

Abstract

Recent efforts have provided convincing evidence for the use of fish scale cortisol concentration in the assessment of long-term stress in fishes. However, cortisol alone is not sufficient to fully describe this state of long-term stress. Dehydroepiandrosterone (DHEA) is an androgen with actions that oppose those of cortisol. The means by which DHEA negates the effects of cortisol occurs in part via changes in the metabolism of cortisol to cortisone. The quantitation of cortisol, DHEA and cortisone could therefore provide a more comprehensive assessment of the overall status of physiological stress. As DHEA and cortisone have yet to be quantified within the fish scale, our first objective was to ensure our sample processing protocol for cortisol was applicable to cortisone and DHEA. Following this, we induced a state of long-term stress in goldfish (Carassius auratus). Some degree of elevation in all hormones was observed in the stressed fish scales. Additionally, cortisol and cortisone were significantly elevated in the stressed fish serum in comparison to controls while DHEA was undetectable in either group. Overall, these results suggest that fish scales provide an appropriate medium for the assessment of long-term stress in fishes via the quantitation of relevant steroid hormones.

Can scale cortisol concentration be quantified non-lethally in wild fish species?

“…Additionally, cortisol concentrations in the scale sample extracts ranged from 0.044 to 0.12 ng/ml and did not show any decline with the increasing number of washes indicating that internal cortisol was not being leached from the whitefish scales for up to five washes. This was additionally confirmed by our previous study in goldfish ( Kennedy and Janz, 2022 ) as scales from this study, washed using the same protocol, had similar cortisol concentrations as a study by Laberge et al (2019 ) that used ultrapure water to wash scales of the same species. This suggests that the choice of wash solvent does not appreciably affect the internal SCC ( Kennedy and Janz, 2022 ).…”

“…This was additionally confirmed by our previous study in goldfish ( Kennedy and Janz, 2022 ) as scales from this study, washed using the same protocol, had similar cortisol concentrations as a study by Laberge et al (2019 ) that used ultrapure water to wash scales of the same species. This suggests that the choice of wash solvent does not appreciably affect the internal SCC ( Kennedy and Janz, 2022 ).…”

“…Nevertheless, these were all adult fish similar in size to the northern pike used in this study. SCC was determined by adapting methods validated in our previous study conducted using goldfish ( Carassius auratus ) from lab-stocks ( Kennedy and Janz, 2022 ).…”

“…However, Carbajal et al (2018 ) suggested that water may be capable of penetrating the scale and removing internal scale hormone and that isopropanol was perhaps not sufficiently aggressive to remove of external hormone contributed by blood or mucus. As mucus contains many compounds insoluble in water such as fatty acids, methanol, a nonpolar solvent previously validated both in our earlier work conducted in goldfish and in the decontamination of hair samples was chosen ( Kroshko et al, 2017 ; Kennedy and Janz, 2022 ). Our previous study in goldfish demonstrated that a minimum of two and a maximum of three washes with methanol was recommended for the removal of external cortisol, DHEA and cortisone from the scale ( Kennedy and Janz, 2022 ).…”

“…As mucus contains many compounds insoluble in water such as fatty acids, methanol, a nonpolar solvent previously validated both in our earlier work conducted in goldfish and in the decontamination of hair samples was chosen ( Kroshko et al, 2017 ; Kennedy and Janz, 2022 ). Our previous study in goldfish demonstrated that a minimum of two and a maximum of three washes with methanol was recommended for the removal of external cortisol, DHEA and cortisone from the scale ( Kennedy and Janz, 2022 ). However, many species of fish used in this study had scales of a greater thickness and larger surface area than goldfish.…”