How do fish take the oxygen out of the water? — Matthew of Huntsville, AL

Dear Matthew,

Instead of lungs (which humans have), God gave fish gills (slits on the side of their heads). A fish breathes by opening its mouth and drawing in a mouthful of water. It then forces the water through its gills by pulling in its throat.

A fish's gill has extremely thin membranes, which allow the oxygen from the water to pass through into the blood vessels of the gill. Then, the much-needed oxygen is carried by the blood to other parts of the fish's body.