All animals need oxygen to survive. Water contains oxygen in dissolved form.
Fish are animals that live in water and "breathe" in water using gills. Most fish cannot breathe out of the water.
Gills are feathery structures found at the side of the head.
Water goes in through the mouth and out through the gills, which take oxygen from the water. Most fishes take gulps of water, and the gill cover (operculum) keeps the water from escaping.
A fish closes its mouth and "pushes" the water out past the gills.
Water flows past the blood in the gills, and the oxygen in the water passes through the thin gill membranes into the fish's blood which then distributes it throughout the body.
Healthy fish gills are bright red due to the high level of oxygen in the blood.
