The Effects of Environmental Enrichment on the Behavior of Laboratory Zebrafish (Danio rerio).

Abstract

Enclosures for laboratory animals are often simple for economic and practical reasons. Enrichment items, such as plants, toys, and refuges, have been shown to improve measures of welfare in commonly used species such as mice and dogs. The numbers of laboratory zebrafish have been increasing in recent years, and most are housed in systems devoid of enrichment. The aim of this study is to assess the impact of environmental enrichment on adult laboratory zebrafish behavior. Experimental fish were raised in the presence of three different enrichment regimes: plastic plants, toys, and photos of gravel. These were compared to a control group raised under standard housing conditions. Once the fish reached sexual maturity, we measured aggression, reproduction, and growth. We found that each enrichment treatment led to significant reductions in aggression in a mirror test compared to control. Reproduction was largely unaffected by the three enrichment treatments. However, we found egg production was decreased following the gravel treatment, and egg survival was increased following the plant treatment. There were no significant impacts of enrichment on measures of growth. In a parallel experiment, breeding fish were exposed to plastic plant enrichment during overnight breeding. Surprisingly, there was no significant impact on egg production or egg survival.