Ontogenetic shift in the schooling behaviour of sardines, Sardina pilchardus

► We explored differences in the schooling behaviour of juvenile and adult sardine. ► Juveniles inhabited subsurface waters and had discrete school structure. ► Sardine shifted behaviour from juvenile to adult school structure at 10.7 cm. ► This was an ontogenetic change coinciding with other changes in biology. ► Feeding demands, competition and predation may affect this behaviour.