High biodiversity may improve fish welfare

In humans, it has been demonstrated a preference for environments with high biodiversity over those with low biodiversity. Moreover, exposure to environments with high biodiversity reduces stress and improves psychological well-being and health. It has been hypothesized that these effects might be the result of selection because individuals able to identify and settle in rich and productive environments with higher biodiversity likely obtain more resources. If this hypothesis is true, the effects of biodiversity on the welfare might be present also in non-human species. To test it, we investigated whether plant biodiversity levels affect welfare and preferences in a fish, the guppy Poecilia reticulata . In a first experiment, guppies' preference for environments with high biodiversity was assessed with a dichotomous choice test. No significant preference was detected, with fish spending equal time in areas with high (3 plant species) and low (1 plant species) biodiversity. In the second experiment of this study, the effect of biodiversity on welfare was examined by raising guppies in different environmental conditions: high biodiversity (3 plant species), low biodiversity (1 plant species), and control conditions (no plants). Behavioral indicators of welfare suggested a positive effect of both high and low biodiversity treatments, although a particular plant species used in the treatments had significant influence. Notably, physiological indicators suggested that the effect on welfare was enhanced in the biodiversity treatment, with fish from this group displaying lower basal cortisol levels. Overall, our results partially support our hypothesis that high biodiversity might positively influence the welfare of guppies, although this effect was primarily due to improved physiological conditions. • We tested fish preferences for high plant biodiversity and its associated benefits • Fish showed no preference in a dichotomous choice for high plant biodiversity • Plant presence reduced anxiety and improved survival • Basal cortisol levels dropped only with multiple plant species present