Nitpick: if in your definition of fish, you mean that they need to both have fins or flippers and be (at least) vaguely hydrodynamic, I don’t think seahorses and puffer fish qualify.
Nitpick: if in your definition of fish, you mean that they need to both have fins or flippers and be (at least) vaguely hydrodynamic, I don’t think seahorses and puffer fish qualify.