Shoaling and schooling
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In biology, any group of fish that stay together for social reasons are shoaling, and if the group is swimming in the same direction in a coordinated manner, they are schooling. In common usage, the terms are sometimes used rather loosely. About one quarter of fish species shoal all their lives, and about one half shoal for part of their lives.
These powder blue tangs are shoaling. They are swimming somewhat independently, but in such a way that they stay connected, forming a social group.
These bluestripe snapper are schooling. They are all swimming in the same direction in a coordinated way.
Schools of forage fish often accompany large predator fish. Here a school of jacks accompany a great barracuda.
A school of fish has many eyes that can scan for food or threats
Common minnow
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The Eurasian minnow, minnow, or common minnow is a small species of freshwater fish in the carp
family Cyprinidae. It is the type species of genus Phoxinus. It is ubiquitous throughout much of Eurasia, from Britain and Spain to eastern Siberia, predominantly in cool streams and well-oxygenated lakes and ponds. It is noted for being a gregarious species, shoaling in large numbers.
Image: Phoxinus
Image: Vairon WIKI800px (cropped)
Minnows shoaling in the shallows at Eglinton Country Park in Scotland