134 T^he Life Story of the Fish 



bladders to keep them from sinking. The shark lives in the 

 open sea, and rarely sinks to bottom. He has no air-bladder, 

 but instead he has an enormous liver full of oil which keeps 

 him afloat. The flounder, on the other hand, is a very solid 

 fish. It has no air-bladder, and you can almost feel the thud 

 with which it lands when it settles on the bottom. It is 

 heavier even than salt water. 



In the much lighter, less buoyant fresh water, it is im- 

 possible for any fish to carry enough fat or oil to keep afloat. 

 Without exception, the fresh-water species which lack the 

 air-bladder are bottom dwellers. To those which wish to 

 carry on their lives on a higher plane, it is indispensable as a 

 float. Without it the pickerel and the muskellunge could 

 not hang motionless in the water, waiting for their preyj 

 without it, the black bass could not hover over its nest, guard- 

 ing its offspring against marauders j and without it the trout 

 and its relatives could not lie for hours just below the surface, 

 rising to take in the food drifting down the stream. Further, 

 to those fish which go from fresh to salt water, or the re- 

 verse, the ability to adjust the air-bladder is indispensable. 

 For a fish in proper adjustment in fresh water will find itself 

 too light when it goes into the heavier salt water, and it 

 will tend to float at the surface unless it can reduce its air- 

 bladder, thus reduce its total volume, and increase its weight- 

 to-volume ratio, its specific gravity, to that of salt water. In 

 the same way, when a fish adjusted to salt water goes into 

 fresh water it will tend to sink unless it can increase its vol- 

 ume. This does not mean that the former fish will be unable 

 to get below the surface, as you are when you bathe in the 

 Great Salt Lake. It does not mean that the latter will be 

 unable to get off the bottom, as even the best human swim- 

 mer is if he falls into an oil-tank. The differences between 

 natural fresh and natural salt water are not so great. What 

 it does mean is that a fish in equilibrium in one will, if he 



