The effect of group size on the behaviour and welfare of four fish species commonly kept in home aquaria

Previous research into fish welfare has focussed particularly on commercially important aquaculture species. However, with over 350 million fishes traded annually within the ornamental fish industry, surprisingly little consideration has been given to the welfare of fish kept in home aquaria. Here, the welfare of four commonly kept species of ornamental fish (neon tetras, white cloud mountain minnows, angelfish and tiger barbs) was investigated in relation to group size. Behaviours including darting, aggression, shoaling and latency to feed were found to vary with group size in a species-specific manner. Neon tetras and white cloud mountain minnows displayed reduced aggression and darting and spent more time shoaling in larger groups. Behavioural patterns were more variable in angelfish and tiger barbs although larger group sizes resulted in increased shoaling. Principal components analysis of the behaviour scores obtained indicated improved welfare in larger groups of neon tetras, white cloud mountain minnows and tiger barbs with no clear link between welfare and group size in angelfish. In conclusion, although the effect of group size on the behaviour of ornamental fish species is species-specific, combination of behavioural parameters within a principal components analysis allows group sizes that promote improved welfare to be identified.