Fish live in aquatic and marine envrionments throughout the world. Fish are vertebrates, meaning they have have a backbone. Fish breath through gills and their skin is generally covered with scales. Almost all species are cold-blooded, but recent discoveries 2 show that warm-blooded fish do exist. There are currently around 30,000 species of fish on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. About 800 of these fish are U.S.-specific. Common fish include sharks, salmon, trout, perch, bass, and sturgeon. Many fish are valued as food for humans and serve as commercially and recreationally important resources 1.
