Meta-analysis shows environmental contaminants elevate cortisol levels in teleost fish - Effect sizes depend on contaminant class and duration of experimental exposure

Glucocorticoid hormones (GCs) help vertebrates maintain homeostasis during and following challenging events. Short-term elevations in GC levels are necessary for survival, whereas longer-term changes can lead to reduced reproductive output and immunosuppression. Persistent environmental contaminants (ECs) are widespread globally. Experimental exposure of individuals to ECs is associated with varying GC responses, within, and across, species and contaminants. Individuals exposed to ECs over long durations are expected to have prolonged GC el-evations, which likely affect their health. We conducted a meta-analysis to test for a relationship between fish GC levels and experimental exposure to ECs, and to explore potential moderators, including duration of exposure, that could help explain the variation in effect sizes within and between studies. We report almost exclusively on cortisol responses of teleost fish to ECs. Although there was much variation in effect sizes, captive-bred fish exposed to ECs had baseline GC levels 1.5x higher than unexposed fish, and fish exposed to pharmaceuticals (es-tradiols and stimulants being mainly considered) had baseline GC levels approximately 2.5x higher than unex-posed fish. We found that captive-bred and wild-caught fish did not differ in GC levels after exposure to the same classes of ECs -studies on captive bred fish may thus enable inferences about GC responses to ECs for wild species. Furthermore, effect sizes did not differ between baseline and challenge-induced GC measures. In dif-ferent analyses, duration of exposure was negatively correlated to effect size, suggesting that the GC response may acclimate after chronic exposure to some ECs which could potentially alter the GC response of EC-exposed fish to novel stressors. Future studies should explore the effect of multiple stressors on the fish GC re-sponse and perform tests on a broader array of contaminant types and vertebrate classes. Crown Copyright (c) 2021 Published by Elsevier B.V. All rights reserved.

Automated summary

Glucocorticoid hormones play a crucial role in maintaining homeostasis in vertebrates, but prolonged exposure to environmental contaminants may result in elevated GC levels, affecting individual health. Fish exposed to environmental contaminants have higher baseline GC levels than unexposed fish, with those exposed to pharmaceuticals showing even higher GC levels.