All fish have gills . These gills absorb oxygen from the water and pass it along to the bloodstream. A fishes scales are called armor because they protect it. A slimy substance moistens the scales. This protects the fish from infection and helps the fish slip through the water faster.
Fish stay afloat because they have swim bladders.
By changing the amount of air in its bladder, a fish never rises or sinks, but stays balanced. Fins move the fish forward, steer it, and help the fish to keep its balance. The pectoral and pelvic fins are used for balance, steering, and braking. The dorsal fin keeps the fish from rolling over and works along with the anal fin. The tail provides power, thrushing the fish forward.