Many fish species are highly social, forming schools of thousands for feeding, predator defense, and navigation. Understanding schooling behavior is essential for appropriate captive husbandry and conservation.
Fish sociality is a welfare consideration that aquarists and researchers are still learning to take seriously. For naturally schooling species, isolation or very small groups cause behavioral indicators of chronic stress. Solo zebrafish, solo neon tetras, solo danios - all commonly kept in undersized groups or alone in aquaria - show elevated stress hormones and abnormal behavioral patterns. The welfare solution is simple: keep schooling species in appropriately sized groups with sufficient tank space for natural schooling behavior to be expressed.