The impact of flow and physical enrichment on preferences in zebrafish

Environmental enrichment is used extensively to improve the welfare of animals in captivity, however, the importance of physical exercise as enrichment is only now coming to light. A key question in assessing the welfare of animals in captivity is, 'What do animals want?' In order to answer this question fully, it is important to determine the role of enrichment, exercise and their interaction on the development of behavior. We housed groups of zebrafish in experimental tanks in which they had free access to four different zones; (i) Enriched only, (ii) Swimming only, (iii) Enriched + Swimming, and (iv) Plain. The tanks also had a central arena where food was delivered. Enrichment included plastic plants and a sandy substrate, and in swimming zones water flow was set at 14 m/s. After four days of acclimatization, behavioral data on zone use was collected, and a preference index was recorded for each replicate tank. Zebrafish showed a significant preference for the Enriched + Swimming zone (0.72 +/- 0.08) but avoided both the Swimming only (-0.28 +/- 0.04) and Plain (-0.31 +/- 0.04) zones spending more time in the central arena (-0.02 +/- 0.04). These results suggest that the combination of both enrichment and exercise is more important than either factor alone. Furthermore, zebrafish prefer enrichment over exercise and even plain tanks when presented with these housing conditions separately. The results highlight the importance of investigating multiple factors simultaneously when assessing preferences for types of housing.