Like us, fish need to breathe oxygen — so how do they do it underwater? It’s a good trick, but evolution has a lot to do if we’re ever to manage it.
As you’ve probably guessed, it has to do with gills, which fish have developed in order to avoid inconvenient trips to the surface. (Marine mammals, such as whales and dolphins, need to visit the surface regularly for air.)
Water contains some oxygen, but not nearly so much as the air.
Here’s how fish use their gills to take the oxygen they need out of the water.
1. The fish opens and closes its mouth to pump water through its gills. (Some fish don’t have a very good pumping system, which means they have to move constantly to keep water flowing through their gills.)
2. Water moves through the fish’s mouth and into its gill filter system, called gill rakers, to strain out anything floating in the water.
3. The water continues through the gills, which contain tiny membranes. These membranes take the oxygen from the water and release carbon dioxide (just as our lungs take oxygen from the air when we breathe in and expel carbon dioxide when we breathe out.)
Gills are very efficient at taking oxygen from water and into the fish’s bloodstreams. But they don’t work on land, because the gills collapse without the buoyancy of the water and the oxygen-rich air is too much for them.
I got this topic from the book, "101 things you need to know". And hoping that it will satisfy our curiosity.
"It was your will and purpose to do this; you have done all these great things in order to instruct me. How great you are, Sovereign LORD! There is none like you; we have always known that you alone are God." (2 Samuel 7:21-22)
Landing a fish: Some fish can breathe on land. The walking catfish can move about on land, taking in air through specialised air-breathing structures attached to its gills. These are spines on its side fins that help it to ‘walk’ — well, wriggle — along.
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ahhhh yun pla un.