Water temperature explains part of the variation in basal plasma cortisol level within and between fish species

Abstract

Within the thermal tolerance range of fish, metabolism is known to escalate with warming. Rapid thermic changes also trigger a series of physiological responses, including activation of the stress axis, producing cortisol. Fish have adapted to their environment by producing a low level of plasmatic cortisol when unstressed (basal), so that thriving in their natural temperature should not impact their basal cortisol levels. Yet, surprisingly, little is known on how temperature affects cortisol within and between fish species. Here, we conducted a phylogenetic meta‐analysis to (1) test whether temperature can explain the differences in basal cortisol between species and (2) evaluate the role of temperature on differences in cortisol levels between individuals of a same species. To do this, we retrieved basal plasma cortisol data from 126 studies, investigating 33 marine and freshwater fish species, and correlated it to water temperature. Intra‐species variability in basal plasma cortisol levels was further investigated in two species: the European sea bass Dicentrarchus labrax and the Nile tilapia Oreochromis niloticus. Factors such as life stage, sex and weight were also considered in the analyses. Overall, our phylogenetic analysis revealed a clear positive correlation between basal cortisol level and the temperature at which the fish live. The role of temperature has also been confirmed within D. labrax, while it failed to be significant in O. niloticus. In this paper, the influence of habitat, life stage, sex and weight on basal plasma cortisol levels is also discussed. Since some abiotic parameters were not included in the analysis, our study is a call to encourage scientists to systematically report other key factors such as dissolved oxygen or salinity to fully depict the temperature‐cortisol relationship in fishes.

Circulating MicroRNAs Indicative of Sex and Stress in the European Seabass (Dicentrarchus labrax): Toward the Identification of New Biomarkers

“…For the stress experiment, we first characterized the stress response of our fish, when exposed to confinement. This was highly challenging since the European seabass has often been regarded as a species with relatively high basal cortisol levels compared to other species (Alfonso et al, 2023). When considering individuals encompassing the same mass range (20-60 mg) the basal level varied between 14 and 80 ng/mL in other studies using a comparable ELISA quantification method (Cerqueira et al, 2020;Tsalafouta et al, 2015).…”

Growth performance, gut microbiota composition, health and welfare of European sea bass (Dicentrarchus labrax) fed an environmentally and economically sustainable low marine protein diet in sea cages

“…Since the levels are similar between diet groups at T4, this could suggest that differences observed at T3 could be linked to a possible acute stress that happened before sampling. It is worth mentioning that care was taken to minimize stress-induced by handling for both fish diet groups during sampling, and that cortisol values measured at T3 for both diet groups were within the range of what can be expected for basal level in European sea bass 74 , 75 . Moreover, we did not measure any significant difference between the two diet groups regarding glucose concentration or in the expression of Hsp70 protein, a reliable stress indicator in fish, including European sea bass 35 (although some high Hsp70 levels were measured in some samples of fish fed the low marine protein diet at both T3 and T4; see Fig.…”

Cortisol as a Stress Indicator in Fish: Sampling Methods, Analytical Techniques, and Organic Pollutant Exposure Assessments

“…Cortisol is a reliable stress indicator produced by the adrenal cortex in the adrenal glands in vertebrates and is considered the major stress-related hormone in teleost fish [ 14 ]. This glucocorticoid (GC) hormone has been widely employed to evaluate several stressor effects in fish, from disease to chemical contaminants [ 15 , 16 , 17 ], water temperature, and photoperiod [ 18 , 19 , 20 , 21 , 22 ], among others.…”