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Synchiropus splendidus" Mandarinfish. Credit: Wikimedian Luc Viatour


A cold-blooded animal with a backbone that lives in water and breathes through gills. Fish are usually covered with scales and have fins for swimming. Most fish lay eggs in the water; others produce eggs inside their bodies and give birth to living young. Fish live in the oceans or freshwater rivers, lakes, and ponds. There are about thirty thousand different kinds of fish, more than all the other vertebrate animals put together. The ancestors of modern fish first appeared in the seas more than 500 million years ago.