Welcome to You Ask Andy

Susan Pares age 12: of Milwaukee, Wisconsin' for her question:

How does a fish breathe underwater?

Andy says, its fun to match a goldfish lazily gliding around his glass home. The handsome fellow gazes out at the worlds opening and shutting his big mouth and gracefully waving his fins. Sooner or 1ater you expect him to come up for air. But he doesn't. Sop you wonder how he manages to breathe under water. And he looks for all the world as though he were solemnly wondering how in the world you manage to breathe out of water.

The fish, of course, belongs to the animal kingdom ands like all animals he needs to breathe oxygen to stay alive. We take our oxygen from the air. About 21% of each breath of air we take in is oxygen. The air we breathe out has about 16% oxygen, plus some carbon dioxide,

Each breath is piped via our noses to our lungs. There it fans out around countless tiny bloodvessels which soak up the oxygen which our bodies needs fuel. The fish has a pair of gills which gather oxygen from the water in very much the same way.

These gills have flaps which might be mistaken for the fish’s ears. Instead of breathing air through his nose, he takes in gulps of water through his mouth. Instead of swallowing it he sends it back through his gills where it fans out and flows around countless tiny blood vessels. They soak up the oxygen the fish needs and send the used water out through the back of the gills. That explains why the fish is forever opening and shutting his mouth. He is breathing.

Since water is made of hydrogen and oxygen, you might suppose that the fish has a way of splitting it  to get his oxygen. Not at all. Most water contains quantities of free oxygen   and this is the oxygen which the fish breathes. This free oxygen gets into the water from the air. Waterfalls, raindrops, rapids and dashing streams add bubbles of air to the water and part of this air is oxygen.

The more oxygen there is present in the water, the more the healthy fish will come along to breathe it. Fish are most plentiful where the great ocean currents mix and churns.  Stagnant water has less free, oxygen than turbulent, tumbling water  The waters of certain. still seas and stagnnt pools are almost free of life.  You will find no fishes there, for there is not enough air in the water for them to breathe,

 

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