Are fish the only animals that have gills?

No, fish are not the only animals with gills. Gills are respiratory organs found in aquatic animals, but not all aquatic animals possess them. Some primitive chordates, such as tunicates (sea squirts) and cephalochordates (lancelets), also have gills. Amphibians, like tadpoles and some salamanders, use gills during their larval stage before they develop lungs for breathing on land.

Additionally, some aquatic crustaceans, such as prawns, crabs, and lobsters, possess gills for extracting oxygen from water.