Posts tagged ‘Fish’s Blood’

How can fish breathe in water?

Fish breathe with gills, which are inside the fish’s head on each side of its throat.  The gills are made of a thin material that allows the fish’s blood to come close to the surface of the gills.  Water contains large amounts of oxygen.

When a fish breathes, it takes a mouthful of water, and then closes its mouth.  This forces the water pass the gills.  The oxygen in the water is absorbed through the think surfaces of the gills, and into the fish’s blood.  The water then leaves the fish’s body through narrow gill slits on each side of its heard.–Dick Rogers

Why fish don’t sink?


A fish, with its bones and scales, is heavier than the water it displaces. Under normal circumstances, it would tend to sink.  But most bony fishes have a balloon-like sac inside their bodies called an “air bladder” that acts as a float to keep them from sinking.  The air bladder fills up with some of the oxygen dissolved in the fish’s blood.

Some fish, such as pike and catfish gulp air at the surface of the water to fill their air bladders.  A shark has no air bladder to buoy it up.  It must constantly be swimming in order to keep from sinking. – Dick Rogers