Fish are vertebrates , which are organisms with backbones. They are cold-blooded , so they can not regulate body temperature. Instead, the temperature changes with the enviornment.
All fish live in water.
Gills, structures in the pharnyx of the fish, allow a fish to breathe. Unlike humans, who have double loop circulation, fish have single loop circulation. The blood is pumped from the heart to gills, where the blood receives oxygen. Then it travels through the body and returns to the heart. For nutrition, fish must consume amino acids.