No experimental evidence of stress-induced hyperthermia in zebrafish (Danio rerio)

Abstract

Stress-induced hyperthermia (SIH) is characterised by a rise in body temperature in response to a stressor. In endotherms, SIH is mediated by the autonomic nervous system, whereas ectotherms must raise their body temperature via behavioural means by moving to warmer areas within their environment (behavioural thermoregulation). A recent study suggested that zebrafish (Danio rerio), an important model species, may move to warmer water in response to handling and confinement and thus exhibit SIH, which, if accepted, may have important practical and welfare implications. However, an alternative hypothesis proposed that the observed movements may be produced by avoidance behaviour rather than behavioural thermoregulation. Investigating the claims for SIH in zebrafish further, we conducted two experiments that extend the earlier study. The first experiment incorporated new conditions that considered fish behaviour in the absence of thermal variation, i.e. their null distribution, an important condition that was not performed in the original study. The second was a refined version of the experiment to reduce the numbers of fish and aid movement between areas for the fish. In contrast to the previous study, we saw no effect of handling or confinement on preference for warmer areas, and no evidence for SIH in either experiment. Instead, we observed a short-lived reduction in preference for warmer areas immediately post-stress. Our work suggests that zebrafish may not experience SIH, and claims regarding fish consciousness based on SIH may need to be revised.

Shade as enrichment: testing preferences for shelter in two model fish species

“…Recent work showing that D. rerio prefer combinations of enrichment types over areas with a single form of enrichment (DePasquale et al ., ) may also imply that the simple forms of shelter in our experiment were not complex enough to elicit a response. Alternatively, the D. rerio in our study, unlike the G. aculeatus , were captive‐bred, had been used in a previous experiment (Jones et al ., ) and may behave differently to wild fish, particularly in response to stressors such as handling and movement between tanks (Huntingford, ). Moreover, captive‐bred fish may be less affected by standard laboratory lighting than wild‐caught fish, since they were raised with it (Villamizar et al ., ), although it can still be a major source of stress (Lidster et al ., ; Morgan & Tromborg, ).…”

“…Scan counts of the number of fish in each zone were obtained from the video recordings at 5 min intervals throughout the experiment. These counts were then used to calculate preference index for each zone-treatment over the duration of the experiment using the Jacobs' preference index (J), as used in similar preference studies (DePasquale et al, 2019;Jones et al, 2018;Kistler et al, 2011;Schroeder et al, 2014). The Jacob's index provides values ranging between +1 (maximum preference) and − 1 (maximum avoidance), with 0 indicating no preference (Jacobs, 1974) as: J = (r − p)((r + p) − 2rp) where r = n area n total −1 , with n area = number of fish in the focal area, n total = number of fish in the tank and p is the available proportion of the focal area out of the total space available in the aquarium (here p = 0.40).…”

“…Recent work showing that D. rerio prefer combinations of enrichment types over areas with a single form of enrichment (DePasquale et al, 2019) may also imply that the simple forms of shelter in our experiment were not complex enough to elicit a response. Alternatively, the D. rerio in our study, unlike the G. aculeatus, were captive-bred, had been used in a previous experiment (Jones et al, 2018) and may behave differently to wild fish, particularly in response to stressors…”

Evidence that stress-induced changes in surface temperature serve a thermoregulatory function

“…lizards: Cabanac and Gosselin, 1993;turtles: Cabanac and Bernieri, 2000; birds: Greenacre andLusby, 2004, andfish: Rey et al, 2015) and the area has attracted significant research attention. Despite such longstanding recognition in philosophical and scientific literature, and near vertebrate-wide conservation (but see Cabanac and Laberge, 1998;Jones et al, 2019), the functional significance of stressinduced changes in body temperature remain elusive. Indeed, while many studies have done well to uncover proximate mechanisms underpinning this phenomenon (i.e.…”

Evidence that stress-induced changes in surface temperature serve a thermoregulatory function

“…lizards: Cabanac and Gosselin, 1993; turtles: Cabanac and Bernieri, 2000; birds: Greenacre and Lusby, 2004, and fish: Rey et al, 2015) and garnered significant research attention. Despite such long-standing recognition in philisophical and scientific literature, and near vertebrate-wide conservation (but see Cabanac and Laberge, 1998; Jones et al, 2019), the functional significance of stress-induced changes in body temperature remain elusive. Indeed, while many studies have done well to uncover proximate mechanisms underpinning this phenomenon (i.e.…”