Do all catfish live in fresh water?

No, there are also species of catfish that live in saltwater environments, such as the ocean. Some examples of saltwater catfish include the gafftopsail catfish, the hardhead catfish, and the sea catfish. These species are typically found in warmer, tropical and subtropical waters around the world. They have adapted to the higher salinity levels of saltwater and often inhabit coastal marine habitats, coral reefs, and estuaries.