The seahorse is a fish
How can you tell if an animal is a fish? Almost all fish have scales. Scales are small round or oval sheets of bone matter. They cover the body of the fish-
Almost all fish have fins. Fish generally have a fin on their back, one in the stomach, one very wide that serves as a tail and two on each side.
Perch is a fish
All fish have gills. They are cuts that are on the fish's head, behind the mouth. Fish breathe through gills.
Scales, fins, guts; the animal that has all these things is a fish.
The eel is a fish