DEDUCTIONS CONCERNING THE AIR BLADDER AND THE 

 SPECIFIC GRAVITY OF FISHES. 



By HARDEN F. TAYLOR, 

 Chief Technologist, U. S. Bureau of Fisheries. 



The function of the air bladder in fishes has been a subject of discussion since the 

 time of Aristotle, all manner of uses having been suggested for it — flotation adjustment, 

 sense organ, manometer, barometer, respiration reservoir, sound producer, steering 

 device, and the like. The most obvious function is that having to do with adjusting 

 the equilibrium of the fish in water, and, knowing as we do the bewildering diversity 

 of modification of most other organs among the thousands of species of fishes which 

 are known, it is not at all surprising that the air bladder has also been adapted to perform 

 many functions other than the principal and obvious one. For a brief description of 

 the air bladder of fishes and a discussion of its functions see Tower (1902), Goodrich 

 (1909), and Giinther (1880). 



It is not necessary in the present connection to consider the various secondary 

 functions of the air bladder. The mere fact of its presence necessarily affects the 

 specific gravity of fishes, and it is on this point that this discussion centers. 



The specific gravity of the fat-free substance of salt-water fish (including backbone, 



but not the head and viscera) can be shown to be about 1.076. For the present purpose 



that figure will be taken for the whole fat-free fish. Full sea water has a specific gravity 



of about 1.026. A 10 kg. fish, fat-free and exclusive of air bladder or other spaces, 



[OOOO ,. , . . .,., . . , 



9293 cc. In order to be in equilibrium with sea water 



would have a volume of 



1. 076 



An air bladder or 



IOOOO 



of the specific gravity mentioned, it should displace — - — - =9746 cc. 



other space of 9746 — 9293=453 cc. is necessary to give the fish the required displace- 

 ment. For water of increasing salinity, from pure fresh water to most concentrated 

 sea water, the following table shows the corresponding air-bladder volume necessary 

 to float each 10 kg. of fish whose specific gravity is 1.076: 



Specific gravity of water. 



1. 000 

 1.005 

 i. 010 

 1. 015 



Volume of 

 air bladder. 



Cc. 



706 

 °S7 

 608 

 S59 



Pressure in 

 air bladder, 

 millimeters 

 mercury. 



760 

 817 

 882 

 9S9 



Specific gravity of watt-r 



I. 020 

 i. ais 



i. 020 

 1.030 



Volume of 

 air bladder. 



Cc. 



S" 



403 



4S3 

 416 



Pressure in 



air bladder. 



millimeters 



mercury. 



1,030 



■»I59 

 i,iS8 

 1,289 



92486°— 22 



