Swim Bladder

One of the ways fish swim down to great depths is to use swim bladders, or gas bladders. These are basically air sacs located within fish to help them regulate their boyancy. The question becomes how does that help anyways?
Oxygen is much more plentiful in the atmosphere than in water. On average there is 210 cubic centimetres of oxygen in one litre of air compared to 10 units in water.
Swim bladders help fish dive to great depths and return to the surface. Some fish must inflate their swim bladders from the atmosphere and others can inflate it by diffussion of oxygen from their lungs. I wanted to quickly look at the evolutionary history of this fish and I found this interesting article that states swim bladders from fish that use the oxygen method to control buoyancy are all related. This means the evolution of this type of method evolved just once. So this is my little post. If you're dying for more biology related information go here.


The earliest fishes, as well as modern cyclostomes, sharks and rays all live without a swim bladder.