Schooling fish have evolved complex social behaviours requiring conspecific company - welfare science shows that isolation causes significant behavioural and physiological stress in these species.
Schooling fish welfare requires recognition that these are highly social animals for whom isolation is not a neutral condition but an active welfare harm. The physiological stress responses of isolated zebrafish and other shoaling species are well-documented. Aquarium husbandry recommendations for species like neon tetras, zebra danios and harlequin rasboras should specify minimum shoal sizes that allow expression of natural schooling behaviour. Research settings using zebrafish must incorporate social housing as both a welfare requirement and a variable affecting experimental validity. Consumer education about minimum group sizes for aquarium fish would improve welfare in the hobby.