Answer:
The correct answer is three.
Explanation:
A fish refers to a kind of species that possesses a backbone, and thrives in the water, and possesses fins. The majority of the fishes exhibit scales covering over their bodies and the majority of them breathe via gills. Fish form a very diverse group, that is, almost half of all the vertebrates are fish.
The fishes are differentiated into three prime kinds, and they are differentiated on the basis of their skeletons and the structure of their mouths. These are cartilaginous fishes, jawless fishes, and the bony fishes. All the mentioned three types are ectotherms or cold-blooded. Of these, the jawless fishes were the most primitive vertebrates, the hagfishes and the lampreys are the only thriving jawless fishes known today.
