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Investigating the effects of highly preferred environmental enrichment on the behaviour and welfare of laboratory zebrafish (Danio rerio)

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Title: Investigating the effects of highly preferred environmental enrichment on the behaviour and welfare of laboratory zebrafish (Danio rerio)
Author: Lavery, Jacqueline Michelle
Department: Department of Integrative Biology
Program: Integrative Biology
Advisor: Mason, Georgia
Abstract: The provision of environmental enrichments (EEs: resources that meet animals’ needs and preferences) tends to improve the welfare of captive animals. Zebrafish (Danio rerio) are a popular model organism typically housed in small, empty tanks; evidence suggests that EE improves their welfare, but which items are preferred has not been extensively investigated with sufficient power, nor have the welfare effects of long-term EE provision (i.e. > 6 months). I first determined zebrafish preferences for a suite of potential EEs, selected based on their ecological relevance. Tests revealed that zebrafish have transitive, ranked preferences for EEs as follows (in order of increasing preference): barren < grass < gravel < grass and gravel. To test the hypothesis that highly preferred EEs improve welfare, I differentially-reared zebrafish in barren tanks and tanks with grass and gravel for up to 24 months. First confirming that the provision of EE did not produce differences in rates of home-tank aggression (which may have represented a confound), I found that fish in enriched tanks have a lower risk of severe morbidity and longer lifespans than their counterparts raised in barren tanks, and are significantly quicker to learn the location of a food reward in a T-maze task likely to be sensitive to chronic stress effects on cognition. These findings support my hypothesis, but the interpretation of other measures I collected is less clear. Fish housed with EE appear more anxious than their barren-reared counterparts in the novel tank and light dark preference test, though this may be confounded by boredom or EE loss. Fish from barren tanks also grew significantly larger than fish from enriched tanks, though why remains unknown. Future work should prioritize assessing whether long-term EE provision promotes zebrafish resilience and behavioural flexibility, as well as testing zebrafish preferences and motivation for EE in more depth. Overall, my findings add to a growing body of literature suggesting that EE improves zebrafish welfare and should be provided where possible, since typical, barren laboratory housing conditions both are not preferred by zebrafish and compromise their survival and cognition.
Date: 2022
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