Sardines swim in enormous schools that twist and turn together as if one animal.

The longer version

Thousands of individuals hold formation by watching only the fish immediately beside them, matching speed and direction within milliseconds. A turn therefore spreads outward as a ripple rather than being ordered from any leader, which is why the mass appears to behave as a single body.

Tight spacing gives every swimmer a smaller chance of being singled out, and constantly changing shape makes targeting one fish difficult. A line of sensitive receptors along each flank reads pressure changes, preventing collisions. Sharing the search also locates food faster, since discoveries spread quickly through the shoal. Shoals also reduce effort, since drafting behind another fish lowers the energy spent swimming.

Where this entry sits

Oceans and Sea Life looks at the salt water that covers most of the planet, from crashing waves and tides to the darkest deep-sea trenches. Expect notes on coral, fish, whales, sharks, jellyfish, shells, and the strange creatures that live far below the surface. The full list sits on the Oceans and Sea Life page, where every entry is listed in order.