The effects of environmental enrichment and environmental stability on the welfare of laboratory zebrafish
Lee, Carole Jean
Date: 21 September 2017
Publisher
University of Exeter
Degree Title
MPhil in Biological Sciences
Abstract
Environmental enrichment involves increasing the complexity of a fish’s environment in order to improve welfare. Researchers are legally obliged to consider the welfare of laboratory animals, including fish; and poor welfare may equate to poor science. Laboratory zebrafish, Danio rerio, are usually kept in bare aquaria for ease of ...
Environmental enrichment involves increasing the complexity of a fish’s environment in order to improve welfare. Researchers are legally obliged to consider the welfare of laboratory animals, including fish; and poor welfare may equate to poor science. Laboratory zebrafish, Danio rerio, are usually kept in bare aquaria for ease of husbandry and, although it is a well-studied species, little is known about the effects on D. rerio of laboratory housing. The first investigation of this thesis shows that environmental enrichment, in the form of gravel and plants, affects survivorship, growth, body condition and behaviour in laboratory-maintained zebrafish. Larvae reared in enriched tanks had significantly higher survivorship than larvae reared in plain tanks. Fish reared in enriched tanks were shorter (20.8 mm) than fish reared in plain tanks (22.7 mm) at 60 days post-fertilisation (pdf) but not at 120 dpf. Females in enriched tanks had higher body condition scores (1.74) than females in plain tanks (1.57) and body condition was more variable in males in plain tanks (1.56 ± 0.14) than in enriched tanks (1.54 ± 0.10). Sex ratio did not differ between treatments. Fish from enriched tanks displayed lower levels of anxiety-like behaviour than fish from plain tanks when acutely transferred to a novel environment. Preference for the enrichment did not differ between treatments but resource monopolisation was higher for enriched fish than for plain fish. Data generated by this study enhance our understanding of what environmental conditions improve housing for laboratory zebrafish.
Although environmental enrichment is often purported as the solution to improving wellbeing in laboratory fish, many enrichments are not compatible with aquaculture or research facilities. The second investigation of this thesis hypothesised that significant welfare benefits may be achievable through simple practical solutions easily adapted to current practices in research laboratories. To investigate these new approaches, this study examined the effects of simple changes in the tank environment on the wellbeing of captive fish, using zebrafish as an experimental model. It was hypothesised that moving fish between tanks of identical status (bare) would provide positive stimulation equating to more complex enriched environments. Groups of zebrafish were housed in ‘stable’ environments (where groups were maintained in the same tanks throughout the study) or in ‘changed’ environments (where groups were periodically moved to novel tanks). Comparisons between treatments included effects on morphometry (length, mass and condition), reproductive success (egg output and viability) and aggressive behaviour. For the simple changes adopted—tank and water—no significant effect of environmental stability was found on body condition, reproductive output or aggression. It was concluded from this pilot study that changing the tank did not have any obvious health benefits to the fish, for the periods of time studied.
MPhil Dissertations
Doctoral College
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