Plankton
Tiny plants and animals that drift in the water and feed most fish, at least when they are young.
Also: phytoplankton, zooplankton
Plankton are living things carried by currents rather than swimming against them. Phytoplankton are tiny algae that use sunlight to grow and make much of the oxygen in the sea. Zooplankton are tiny animals, such as copepods, krill and the larvae of fish, crabs and corals, that eat phytoplankton or each other. Nearly all fish larvae live in the plankton and feed on it, and many adult fish, from sardines to whale sharks, eat it all their lives. Where plankton is rich, as in upwelling zones, fisheries are rich too.