Animalia > Chordata > Actinopterygii/Chondrichthyes

Fish are cold-blooded, strictly aquatic craniate vertebrates that include the bony fishes and usually the cartilaginous and jawless fishes and that have typically an elongated somewhat spindle-shaped body terminating in a broad caudal fin, limbs in the form of fins when present at all, and a two-chambered heart by which blood is sent through thoracic gills to be oxygenated.