Effects of Holding Density on the Welfare of Zebrafish: A Systematic Review

Abstract

The zebrafish is becoming an increasingly popular research animal around the world. Its welfare is affected by an array of environmental factors, such as food access and water quality. Holding density is an important welfare aspect, not least due to its interaction with other housing conditions. Despite the extensive use of zebrafish in research, little is known of how densities affect its welfare. In this systematic review, we have performed a large literature search, compiled, and evaluated all publications regarding zebrafish holding density. We have analyzed how density effects growth, reproduction, and stress response, including behavior, water quality, and pathogenic outbreaks in young and adult fish. Our review shows that the holding densities tested vary largely depending on the research focus, for example, body growth or behavior. In fact, research indicates that future recommendations on holding density could depend on which welfare aspects are considered. Overall, there is a need for more studies investigating the interactive effects of density on welfare indicators, such as reproduction coupled with stress response. We stress the necessity of including holding density in universal housing guidelines and reporting information on holding conditions of larvae and adults when publishing zebrafish work.

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

“…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 ).…”

Novel husbandry practices result in rapid rates of growth and sexual maturation without impacting adult behavior in the blind Mexican cavefish

“…Changes to animal care can impact animal behavior and therefore influence the reproducibility of behavioral studies 10, 45, 46 . To determine whether our changes in animal care could impact behavior, we utilized standard protocols for published behavioral assays at the individual and group level 32, 47 .…”

Performance of Co-Housed Neon Tetras (Paracheirodon innesi) and Glowlight Rasboras (Trigonostigma hengeli) Fed Commercial Flakes and Lyophilized Natural Food

“…Albeit the initial fish stocks in our study were in between these numbers (eight per species), it nevertheless will be a reasonable idea to follow such scientifically verified outlines in future research on small ornamentals (especially when studying community aquaria), which means keeping the fish in groups of 10+ individuals of each species. It needs to be considered, however, that larger tanks will likely be required to avoid overcrowding, as this may cause stress and anxiety, and often accelerates the onset of diseases [ 86 ].…”

“…In ornamental fish, it is known that excessive stocking density may increase the risk of body deformation, but only at very high numbers, typically found in zebrafish housing systems of research facilities rather than in regular aquaria or even wholesaler tanks (above 12 fish L −1 ) [ 86 ]. Meanwhile, aquaculture research shows that skeletal deformities are relatively frequent in some farmed fish species [ 73 ] and can be prompted by a number of reasons [ 74 ], although improper nutrition remains to be the main causative factor.…”