Everything a fish does it does in water, and living in water requires an entirely different anatomy than living on land. The obvious difference is in the way fish breathe. Instead of breathing with lungs, fish obtain oxygen using gills. As water passes across the gills, oxygen molecules dissolved in the water diffuse across the gill membrane and enter the bloodstream. Wastes move in the opposite direction and are carried away. Fins are another difference. The tail or caudal fin propels the fish through the water. The dorsal and anal fins provide stability. The pectoral and pelvic fin allow the fish to steer. Even fish skin is different. Instead of hair or fur, fish skin is covered with scales that are in turn protected by a film of mucous. Explore this distinctive anatomy by clicking on the buttons below.