Housing Environment Affects Baseline Anxiety in Zebrafish

Abstract

Neuroscience researchers that wish to address compelling questions in psychopharmacology would benefit from the use of zebrafish, which have a behavioral repertoire that is rich and complex and that reflects many fundamental processes in humans, such as those that evoke anxiety. Zebrafish behavior is easily quantified in diverse test environments, but it is important to consider the conditions used to house the fish, prior to the behavioral testing, when designing experiments. Studies show that fish housed at high densities exhibit elevated cortisol levels as compared with fish housed at lower densities. The literature is less clear about the behavioral consequences of housing and handling. We examined the effects of housing (group versus paired) on several behavioral parameters. We observed that group-housed fish exhibited an anxious phenotype as evidenced by tank diving and meandering. Other more general indicators of movement and spatial navigation were unaffected by housing. This study focused on two specific housing environments, and the results support the need for continued research in this area to further elucidate the contributions of housing and handling on the subtleties of zebrafish behavioral markers.

The effect of fish density and tank size on the behavior of adult zebrafish: A systematic analysis

“…Furthermore, paradoxically, whole-body cortisol levels were also found reduced in chronically isolated fish, a change that was accompanied by reduced bottom dwell time, a behavioral sign of diminished anxiety (Shams et al, 2015(Shams et al, , 2017b. These results suggested that zebrafish forced to be in dense groups in small tanks may experience elevated stress 10.3389/fnbeh.2022.934809 and/or anxiety (Parker et al, 2012;Movva et al, 2017). Lower cortisol release rates were also demonstrated in group-housed zebrafish that were exposed to short term (1 h) or long-term (2 weeks) social isolation as compared to group-housed controls (Lindsey and Tropepe, 2014).…”

“…However, with the increasingly sophisticated methods employed in current zebrafish biology research and the expected finer phenotypical changes resulting from a variety of manipulations, including those affecting brain function and behavior, zebrafish researchers need to revisit the question of whether the current industry standard of crowding zebrafish into small tanks may impact the studied phenotypes. Sporadic studies have already started to imply that housing zebrafish in the standard manner may have deleterious consequences ( Ramsay et al, 2006 ; Reed and Jennings, 2011 ; Parker et al, 2012 ; Pavlidis et al, 2013 ; Lindsey and Tropepe, 2014 ; Shams et al, 2015 , 2017a , b ; Movva et al, 2017 ; Maierdiyali et al, 2020 ; Stevens et al, 2021 ). Surprisingly, despite the increasing popularity and frequent use of zebrafish in biomedical research, little is known about what constitutes an optimal housing environment for these fish in the laboratory, and no systematic analysis has been performed to address this question ( Ramsay et al, 2006 ; Reed and Jennings, 2011 ; Andersson and Kettunen, 2021 ).…”

“…The zebrafish is a highly social species. In their natural environment, these fish form shoals ranging from two to several hundred individuals, an important adaptive strategy that reduces predation risk and increases foraging efficiency and mating success (Miller and Gerlai, 2011 ; Shams et al, 2015 , 2017a , b ; Movva et al, 2017 ; Tunbak et al, 2020 ; Stevens et al, 2021 ). Although zebrafish are highly social and shoal in the laboratory too, these fish do not live in confined, cave-like environments, but inhabit open, spacious bodies of water ( Ramsay et al, 2006 ; Reed and Jennings, 2011 ).…”

“…Indeed, recent studies have already begun to imply that the current method of housing zebrafish in large numbers in small tanks is suboptimal likely leading to conditions that may negatively impact a plethora of biological phenotypes including brain function and behavior ( Ramsay et al, 2006 ; Reed and Jennings, 2011 ; Parker et al, 2012 ; Pavlidis et al, 2013 ; Lindsey and Tropepe, 2014 ; Shams et al, 2015 , 2017a , b ; Movva et al, 2017 ; Maierdiyali et al, 2020 ; Stevens et al, 2021 ). For example, unexpectedly, housing the highly social zebrafish singly was found to reduce anxiety-like responses (e.g., hyperactivity and thigmotaxis) compared to the behavior of zebrafish housed in a standard crowded manner ( Shams et al, 2017a ).…”

“…Lower cortisol release rates were also demonstrated in group-housed zebrafish that were exposed to short term (1 h) or long-term (2 weeks) social isolation as compared to group-housed controls ( Lindsey and Tropepe, 2014 ). Similarly, when zebrafish were housed in lager groups versus housed as pairs, the former showed behavioral signs of elevated anxiety including increased diving, meandering, bottom dwelling and angular velocity ( Movva et al, 2017 ; Stevens et al, 2021 ). In accordance with these findings, whole-body cortisol levels of zebrafish housed in crowded (40 fish/L) versus non-crowded (0.25 fish/L) tanks were found to be significantly elevated in the former ( Ramsay et al, 2006 ).…”