Effects of an experimental short‐term cortisol challenge on the behaviour of wild creek chub Semotilus atromaculatus in mesocosm and stream environments

Abstract

The consequences of stress on the behaviour of wild creek chub Semotilus atromaculatus outside the reproductive period were studied using a single intra-coelomic injection of cortisol, suspended in coconut butter, to experimentally raise plasma cortisol levels. Behaviour between cortisol-treated, sham-treated (injected with coconut butter) and control S. atromaculatus was compared in a mesocosm system, using a passive integrated transponder array, and in a natural stream system (excluding shams), using surgically implanted radio transmitters. While laboratory time-course studies revealed that the cortisol injection provided a physiologically relevant challenge, causing prolonged (c. 3 days) elevations of plasma cortisol similar to that achieved with a standardized chasing protocol, no differences in fine-scale movements were observed between cortisol-treated, sham-treated and control S. atromaculatus nor in the large-scale movements of cortisol-treated and control S. atromaculatus. Moreover, no differences were observed in diel activity patterns among treatments. Differential mortality, however, occurred starting 10 days after treatment where cortisol-treated S. atromaculatus exhibited nearly twice as many mortalities as shams and controls. These results suggest that, although the experimental manipulation of cortisol titres was sufficient to cause mortality in some individuals, there were compensatory mechanisms that maintained behaviours (i.e. including activity and movement) prior to death. This study is one of the first to use experimental cortisol implants outside a laboratory environment and during the non-reproductive period and yields insight into how wild animals respond to additional challenges (in this case elevated cortisol) using ecologically meaningful endpoints.

An experimental field evaluation of winter carryover effects in semi‐anadromous brown trout (Salmo trutta)

“…Conversely, a chronic stressor (e.g., confinement or crowding) has prolonged elevation (∼4 weeks) but lower magnitude (10–20 ng ml −1 ; reviewed in Pickering, ). Therefore, the magnitude of cortisol elevation targeted in this study was on the upper end of ecologically relevant values and the extended duration was consistent with the notion of a semi‐chronic stress (Nagrodski et al, ). Unfortunately, sham treatments (receive injection of only cocoa butter) were not included in the study due to low numbers of captured brown trout in the desired size range (>120 mm total length).…”

Does cortisol manipulation influence outmigration behaviour, survival and growth of sea trout? A field test of carryover effects in wild fish

“…Despite their potential ecological importance, there is a shortage of studies that document the response of wild fish to stress in their natural environment and its potential for carryover effects , O'Connor et al 2011, Nagrodski et al 2013. For sea trout, little work has been done to understand relationships between ecology (e.g.…”

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). As such, it is possible that some important components of the stress response were not integrated into our experimental approach.…”