Cortisol release in response to UVB exposure in Xiphophorus fish

Abstract

Xiphophorus fishes are comprised of 26 known species. Interspecies hybridization between select species has been utilized to produce experimental models to study melanoma development. Xiphophorus melanoma induction protocols utilize ultraviolet light (UVB) to induce DNA damage and associated downstream tumorigenesis. However, the impact of induced stress caused by the UVB treatment of the experimental animals undergoing tumor induction protocols has not been assessed. Stress is an adaptive physiological response to excessive or unpredictable environmental stimuli. The stress response in fishes may be measured by assay of cortisol released into the water. Here, we present results from investigations of stress response during experimental treatment and UVB exposure in X. maculatus Jp 163 B, X. couchianus, and F1 interspecies hybrids produced from the mating X. maculatus Jp 163 B x X. couchianus. Overall, cortisol release rates for males and females after UVB exposure showed no statistical differences. At lower UVB doses (8 and 16 kJ/m2), X. couchianus exhibited 2 fold higher levels of DNA damage then either X. maculatus or the F1 hybrid. However, based on cortisol release rates, none of the fish types tested induced a primary stress response at the UVB lower doses (8 and 16 kJ/m2). In contrast, at a very high UVB dose (32 kJ/m2) both X. maculatus and the F1 hybrid showed a 5 fold increase in cortisol release rate. To determine the effect of pigmentation on UVB induced stress, wild type and albino X. hellerii were exposed to UVB (32 kJ/m2). Albino X. hellerii exhibited 3.7 fold increase in cortisol release while wild type X. hellerii did not exhibit a significant cortisol response to UVB. Overall, the data suggest the rather low UVB doses often employed in tumour induction protocols do not induce a primary stress response in Xiphophorus fishes.

Fluorescent light exposure incites acute and prolonged immune responses in zebrafish (Danio rerio) skin

“…Different wavelengths of light have also been shown to suppress melatonin secretion (Brainard et al, 1985; Thapan et al, 2001). However, except for our recent reports, specific responses in gene expression that occur when an intact animal is exposed to various types of FL have not been extensively studied (Boswell et al, 2015; Chang et al, 2015; Contreras et al, 2014; Lu et al, 2015; Walter et al, 2014; Walter et al, 2015; Yang et al, 2014).…”

Measuring cortisol, the major stress hormone in fishes

“…Therefore, we might expect that the former would release cortisol at a quicker rate than the latter, although this remains to be demonstrated. Cortisol release rate could also be normalised by standard length in lieu of mass (Contreras et al, ; Gabor & Contreras, ; Geffroy et al, ). Other abiotic parameters such as temperature and salinity have not yet been taken into account, although they undoubtedly modify release rates of cortisol.…”

“…A way to counteract this is to habituate the fish by exposing it several times ( e.g ., 3–4 times) to the beaker, as done for Amatitlania nigrofasciata (Günther 1867) (Wong et al, ) and Poecilia latipinna (Lesueur 1821) (Gabor & Contreras, ). Another option would be to trap the fish carefully while in its usual environment (Boulton et al, ) or to acclimate it overnight in the beaker and renew the water (Contreras et al, ). The mean release rate of studied fishes in Table (excluding zebrafish Danio rerio (Hamilton 1822) from Félix et al, , which is a clear outlier) is 0.3 ng g −1 h −1 .…”