Measuring water‐borne cortisol in Poecilia latipinna:is the process stressful, can stress be minimized and is cortisol correlated with sex steroid release rates?

Abstract

The stress of water-borne hormone collection process was examined in sailfin mollies Poecilia latipinna. Baseline release rates of the stress hormone cortisol were measured and minimum confinement time for water sampling was evaluated for a standard 60 min v. a 30 min protocol. A 30 min hormone collection period reflects release rates over 60 min. Potential stress response to confinement in the beaker for the water-borne collection process was tested over 4 days. There was no evidence of stress due to the collection methods, as cortisol release rates did not differ significantly across four sequential days of handling for P. latipinna. Males and females did not differ significantly in baseline cortisol release rates. Baseline cortisol release rates from fish immediately after being collected in the field were also not significantly different than those in the 4 day confinement experiment. After exposure to a novel environment, however, P. latipinna mounted a stress response. Stress may also affect sex steroids and behaviour but cortisol release rates were not significantly correlated with sex steroids [11-ketotestosterone (KT), testosterone, or oestradiol], or mating attempts. The correlation between water-borne release rates and plasma steroid levels was validated for both cortisol and KT. Finally, normalizing cortisol release rates using standard length in lieu of mass is viable and accurate. Water-borne hormone assays are a valuable tool for investigating questions concerning the role of hormones in mediating stress responses and reproductive behaviours in P. latipinna and other livebearing fishes.

Disruption of the stress response in wastewater treatment works effluent-exposed three-spined sticklebacks persists after translocation to an unpolluted environment

“…Overall, WC release rates, which provide a surrogate for blood cortisol concentrations (Félix et al 2013;Friesen et al 2012;Gabor and Contreras 2012;Wong et al 2008), were directly proportional to the estimated concentration of WWTW effluent at these sites. Female sticklebacks translocated from the same sites five months previously and subsequently held in pristine aquarium conditions continued to exhibit the same site-related trends in WC release rates as their more recently wild-caught counterparts.…”

“…Instead, the magnitude of the stress response was measured indirectly via the release of cortisol across the gill epithelium to the surrounding water (Scott and Ellis 2007) the rate of which varies in proportion with blood cortisol concentrations (Félix et al 2013;Friesen et al 2012;Gabor and Contreras 2012;Wong et al 2008). During March 2014 five fish were transferred by handnet from a holding tank to a bucket containing 5 litres of water in which they remained for 30 mins before being transferred to individual Nalgene tubs (150 ml, 6.5 cm diameter, with screw-fit lids) containing 100 ml of artificial freshwater (deionised water containing 0.33 g/l aquarium grade sea salt; Klüttgen et al 1994).…”

A comparison of two methods for the assessment of stress axis activity in wild fish in relation to wastewater effluent exposure

“…In fish, circulating steroids, including cortisol, are transferred from the bloodstream to the surrounding water across the gill epithelium (Ellis et al, 2005) and can be quantified after extraction and concentration of water samples from holding tanks or collection vessels. Steroids retained in water samples after transfer across the gill may be a more accurate surrogate of blood steroid levels than the multi-compartment total provided by WBIC: the rate of release of 6 cortisol to water has been shown to be proportional to the concentration of cortisol in the blood in a number of species (Félix et al, 2013;Gabor and Contreras, 2012;Scott and Ellis, 2007;Wong et al, 2008) including three-spined sticklebacks (Sebire et al, 2007). The release of cortisol to water is an endpoint that is ideally suited to the assessment of stress responsiveness in small fish captured from field environments, in circumstances where blood sampling is not possible.…”

Cortisol release in response to UVB exposure in Xiphophorus fish

“…This is especially important for smaller fish that have very low amounts of blood available for sampling. Cortisol secreted into the water has been correlated with circulating blood cortisol concentrations in live bearing fishes and shown to provide an accurate relative measurement of released cortisol due to interaction with a primary stressor (Gabor and Contreras, 2012). The correlation between circulating and water-borne cortisol is due to free diffusion rates of steroids across gill tissues in which release rates are relative to the surface area of the gills.…”

“…The correlation between circulating and water-borne cortisol is due to free diffusion rates of steroids across gill tissues in which release rates are relative to the surface area of the gills. Since fish mass and length measurements are considered proportional to gill surface area both provide a useful value for normalizing cortisol release rates among fish of different sizes (Gabor and Contreras, 2012; Scott et al, 2008). Thus, teleost fish provide a reliable vertebrate model where cortisol release may be used to characterize the primary stress response.…”