Quick Definition
A loosely aggregated social group of fish of the same species that remain in proximity but without the strict alignment of a school.
📖 Full Definition
A shoal is any group of fish of the same species that remain together for social reasons. Unlike a school, shoal members are not necessarily aligned or swimming in a coordinated manner — they may be stationary, feeding, or moving independently. All schools are shoals, but not all shoals are schools. Fish form shoals because being in a group reduces individual predation risk (dilution effect) and improves foraging through information transfer.
💡 Examples & Context
Resting perch in a weedy lake margin form a shoal. When a predator approaches, the group may coalesce into a polarised school and flee.