They use their gills.
gills
Fish extract dissolved oxygen from the water by passing the water through their gill slits. Inside the gills is very thin tissue that can 'grab' oxygen right out of the water and put carbon dioxide waste into the water.
GILLS!!
Tadpoles get oxygen from water like fish do.
Oxygen. Aquatic animals need it too. They just have to be a lot more efficient at getting it. Air is about 21% oxygen, that's 210,000 parts per million. In most natural water sources, dissolved oxygen is about 14 parts per million. But if it's not there - your fish die.
They are parts of the body of fish, snakes, or pangolin.
the gills of a fish take in oxygen in water while the human lung take in oxygen in the air. I think...
Fish can absorb water by the gills
Water can be depleted of it's oxygen by a number of different ways. Short of putting the water in a vacuum and "sucking" the dissolved oxygen out, oxygen-breathing organisms such as fish take oxygen from the water through respiration, for example. It is unlikely a large body of water to become completely deoxygenated due to the presence of photosynthetic aquatic organisms (plants) and the fact that oxygen is also dissolved in the water at the water's surface.
The gills are flat plates inside the body of the fish behind the eyes that are covered with blood vessels near the surface that can absorb dissolved oxygen from the water and disperse carbon dioxide from the fish's body.
The property of water that allows fish to breathe is its ability to dissolve oxygen. As water flows over the fish's gills, oxygen molecules from the water diffuse into their bloodstream, allowing them to extract oxygen for respiration.
The way in which insects and fish breathe differs in the process in which each receives oxygen. Insects use a tracheal system to receive oxygen and fish use their gills to filter oxygen out of the water.