Supraphysiological Cortisol Elevation Alters the Response of Wild Bluegill Sunfish to Subsequent Stressors

Abstract

Wild fish are frequently exposed to multiple stressors, but the influence of previous or ongoing stress on an animal's subsequent response is poorly understood. Using wild-caught bluegill sunfish (Lepomis macrochirus) as a model, we used exogenous hormone implants to experimentally raise circulating cortisol in a group of fish for ∼10 days. We also maintained sham-treated and control groups of fish. We subjected all animals to a secondary stressor in the form of either a heat challenge or fasting challenge. We compared survival, body condition, and plasma-borne indicators of physiological status among cortisol-treated, sham-treated, and control groups following the secondary stressor. In order to compare short- and long-term effects of cortisol treatment, we initiated the secondary stressor either 4 or 30 days following initial cortisol treatment. Cortisol-treated fish succumbed to the fasting challenge sooner than sham-treated and control fish at both 4 and 30 days. Interestingly, cortisol-treated fish lost equilibrium sooner than sham-treated and control fish during the heat challenge when conducted at 30 days, but not at 4 days. These results demonstrate that multiple simultaneous stressors have cumulative effects on bluegill sunfish. Furthermore, these results demonstrate that supraphysiological cortisol doses alter the long-term responses of bluegill sunfish to additional challenges, even after apparent recovery. Such cumulative and long-term effects may be an important factor in mediating the response of wild animals to natural and anthropogenic stressors, and should be considered in ecological studies.

Biological carryover effects: linking common concepts and mechanisms in ecology and evolution

“…Few studies have identified specific mechanisms underlying carryover effects, and when mechanisms have been identified, it remains largely unknown whether or not these effects are reversible. For example, even brief elevations of corticosteroid stress hormones have been shown to cause within-season carryover effects on responses to secondary challenges (McConnachie et al 2012) and long-term seasonal carryover effects on growth and mortality rates (O'Connor et al , 2011. While carryover effects in these cases are mediated by the endocrine system, it is unknown whether changes in the regulation of genes associated with the stress axis are involved, or whether these changes are reversible.…”

Is winter worse for stressed fish? The consequences of exogenous cortisol manipulation on over-winter survival and condition of juvenile largemouth bass

“…Based on previous studies using similar protocols (O'Connor et al, 2009;McConnachie et al, 2012), we estimate that cortisol elevation persisted in our experimental fish for between one and two weeks, simulating a semi-chronic stress event. The administration of cortisol mimics the cortisol-dependent processes associated with stress response, but it does not mimic the sensory aspects or the neuroendocrine activation of the HPI axis (Nagrodski et al, 2013).…”

“…Validations with largemouth bass using the same concentrations of cortisol and cocoa butter yielded ecologically-relevant cortisol titers in the blood of 157 ± 47 ng mL −1 (mean ± standard error of the mean, SEM; O' Connor et al, 2013), which is consistent with endogenous levels found in largemouth bass following exhaustive exercise (O'Connor et al, 2009). We did not measure the precise time course of the cortisol elevation in our fish; however, based on previous studies in largemouth bass using slightly different protocols (O'Connor et al, 2009), and bluegill sunfish (Lepomis macrochirus) using the same protocol (McConnachie et al, 2012), we estimate that the cortisol elevation lasted between one and two weeks. Following the tagging and cocoa butter implantation procedures, fish were transferred to one of two identical on-site 400 m 2 experimental ponds (ponds 4 and 6), where they were placed in floating net pens for seven days to monitor acute mortality.…”

An Overview of Literature Topics Related to Current Concepts, Methods, Tools, and Applications for Cumulative Risk Assessment (2007–2016)

“…According to Holmstrup et al [93], the majority of cumulative ecological risk studies of chemical and nonchemical stressors have looked at only two factors. Some studies demonstrated methods and models new to ecological health, for instance, a fish model of chronic stress or metabolomics approaches to mixture identification and investigation of effects [100,102,142]. A recent ecological risk study demonstrates integration of a combination of 12 chemical and nonchemical stressor using Bayesian modeling techniques [112].…”