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

Abstract

Cortisol, the primary glucocorticoid in fishes, is secreted into the bloodstream in response to stress. Circulating cortisol accumulates in scales, a durable calcified structure that can be easily sampled from many fish species. As such, the use of scale cortisol concentration (SCC) is currently being explored as a means of chronic stress biomonitoring in wild fishes. Scales serve an important role in fish physiology and thus the number of scales required for reliable cortisol analysis is a limiting factor in the non-lethal collection of such samples. To date, scale cortisol quantification has also only been performed non-lethally in captive fishes and due to differences in stress responsiveness SCCs likely differ in wild species. As such, this study aimed to (1) apply our fish scale processing and analysis protocol to wild fish species and (2) apply it to five north temperate fish species to provide information useful to future non-lethal scale sampling regimes. Cortisol was successfully measured in scales collected from wild northern pike (Esox lucius), walleye (Sander vitreus), whitefish (Coregonus clupeaformis), white sucker (Catostomus commersonii) and captive rainbow trout (Oncorhynchus mykiss). SCCs were significantly different between species and thus the sample mass required for reliable cortisol analysis differed as well. In addition to the size of the fish and the mass of their scales this is an important consideration for future scale cortisol analyses as these factors could make SCC an attainable non-lethal sample matrix in some species of fish but impractical in others.

Effect of Feeding Common Carp with Different Quantities of a Certified Commercial Feed on Haematological Parameters, Blood Indicators and Cortisol Hormone Levels

“…Cortisol helps in energy mobilization as a response to any external pressure, and cortisol receptors are distributed throughout the body, providing additional opportunities for detrimental effects on fish. Prolonged exposure to stress makes fish more vulnerable to immunosuppression, osmotic disturbances, and reduced immunity [3]. Cortisol levels have a significant impact on nutrition, including immune response, metabolic regulation through energy reallocation, and coping with environmental stressors and behavioral habits.…”

Validation of Non-lethal Biopsy Techniques in Freshwater Fish

“…During a stressor, cortisol is secreted into the bloodstream from adrenal glands (Aedo et al 2023). Once secreted, cortisol binds to Glucocorticoid Receptor 1 and initiates a molecular cascade which allows the fish to respond to the stressor, such as by increasing metabolism and energy production which may be crucial for burst swimming required for predator avoidance or during angling interactions (Lawrence et al 2019;Kennedy and Janz 2023). Although beneficial for short term stress response, long-term upregulation may sequester energy from other essential functions (e.g., growth, reproduction, osmoregulation) (Kennedy and Janz 2023).…”

“…Once secreted, cortisol binds to Glucocorticoid Receptor 1 and initiates a molecular cascade which allows the fish to respond to the stressor, such as by increasing metabolism and energy production which may be crucial for burst swimming required for predator avoidance or during angling interactions (Lawrence et al 2019;Kennedy and Janz 2023). Although beneficial for short term stress response, long-term upregulation may sequester energy from other essential functions (e.g., growth, reproduction, osmoregulation) (Kennedy and Janz 2023). The degree to which cortisol levels (and subsequent upregulation of Glucocorticoid Receptor 1) can vary widely between fish species (Vallejos-Vidal et al 2022), and quantification of stress based on expression requires specific previous knowledge on species and population (Aedo et al 2023).…”