[countable] a creature that lives in water, breathes through gills, and uses fins and a tail for swimming They caught several fish. tropical/marine/freshwater fish shoals (= groups) of fish a fish tank/pond There are about 30 000 species of fish in the world. The list of endangered species includes nearly 600 fishes. Fish stocks in the Baltic are in decline. In the pool she could see little silvery fish darting around.