What do zebrafish want? Impact of social grouping, dominance and gender on preference for enrichment

Although environmental enrichment is known to improve laboratory rodent wellbeing and enhance scientific data collection, relatively little is known with regards to the type of enrichment that might be useful for zebrafish (Danio rerio). Therefore, this study explored if zebrafish displayed preferences for a range of enrichments, including substrates, artificial plants, combinations thereof and airstones. Tanks divided into two compartments containing different enrichment cues were used to determine the preferences of zebrafish housed in pairs and groups of eight. When comparing time spent in enriched versus barren compartments, dominant individuals in a pair displayed a preference for substrate and behaviourally excluded the subordinate (p<0.05). In groups there was a preference for all substrate (p<0.01) and plant (p<0.05) enrichments over barren conditions. The strongest preference was for gravel substrate and images of gravel attached to the bottom of the tank. When preferences were compared for different enrichments, gravel (both sexes, p<0.01) again emerged as the cue attracting the most significant preferences, with any combination featuring gravel substrate preferred over any combination featuring sand (p<0.05). The study has demonstrated that zebrafish reared in barren conditions preferred structural enrichment over standard conditions; however, when fish were held in pairs this was influenced by dominance status and in groups this was influenced by gender.