Why is seahorse a fish?

After much debate over the years, scientists finally that seahorses are fish. They breathe using gills, have a swim bladder to control their buoyancy, and are classified in the Class Actinopterygii, the bony fish, which also includes larger fish such as cod and tuna. Seahorses have interlocking plates on the outside of their body, and this covers a spine made of bone. While they have no tail fins, they have 4 other fins - one at the base of the tail, one under the belly and one behind each cheek.