Fish were the first animals with backbones, and they've been refining the formula for over 500 million years.
There are more species of fish than every other vertebrate group combined — over 34,000 known species, with new ones described every year. Every land vertebrate, including you, descends from a small fish that crawled out of a Devonian swamp roughly 375 million years ago.
Modern fish range from finger-sized gobies to whale sharks the length of a school bus. They navigate by magnetism, communicate by sound and electricity, and some species can change sex mid-life depending on the social demands of their group.
These verified facts cover fish biology, deep-sea oddities, the strangest species, and the surprising overlap between fish behavior and what we used to think only mammals did.
Below: every fact from our verified archive that touches this topic. Each is independently sourced; click through to its dedicated page.