There are around 1,270 species of killifish and almost any warm water climate in the world has a species of killifish somewhere, or record that a species of killifish once existed there. Killifish are found mainly in fresh or brackish waters in the Americas, as far south as Argentina and as far north as southern Ontario and even Newfoundland and Labrador.^[5] There are also species in southern Europe, in much of Africa as far south as KwaZulu-Natal, South Africa, in the Middle East and Asia (as far east as Vietnam), and on several Indian Ocean islands.

The species vary in coloration and finnage, and though they are closely related to live-bearing tooth carps, they are egg-laying fish—but in a way unlike any other fish on the planet.

Speculation has circulated for years about where these strange, colorful, short-lived little fish came from or why they evolved everywhere there is warm water. The majority of killifish live between two and three years.