224 VICTOR E. SHELFORD AND W. C. ALLEE 



would be as detrimental to fish in the long run as a more con- 

 stant low oxygen content. In our experience with low oxygen 

 content, the smaller A.mploblites are more hardy and the small 

 Abramis are more sensitive than the adults. The data at hand 

 suggest that there is some relation between habitat preference 

 and the amount of oxygen necessary to maintain life. 



3. THE EFFECT OF CARBON DIOXIDE AND AMMONIA 



Many physiologists hold that carbon dioxide is more important 

 than oxygen as a stimulant for respiratory action. In general 

 its action is that of a narcotic, stimulating in small quantities, 

 intoxicating in larger quantities, and producing death when taken 

 in very large quantities. Similar behavior results have often been 

 obtained with carbon dioxide and with acids. Both acids (Marsh 

 '10, p. 896) and carbon dioxide are fatal to fishes when present 

 in quantity. Reuss ('10, p. 555) worked with the effect of vary- 

 ing amounts of carbon dioxide upon the rainbow trout and found 

 its general effect to be entirely similar to that with higher verte- 

 brates. Up to about 15 cc. per liter, carbon dioxide acted as a 

 stimulant to respiratory movements. Beyond this breathing did 

 not become stronger. Staggering occurred with a concentration 

 of from 25 to 41 cc. per liter and a total loss of equilibrium at 

 from 44 to 53.5 cc. per liter. Weigelt ('85, p. 82) working with 

 carp and trout, found that 35 to 37.5 cc. of carbon dioxide per 

 liter had no effect but that 50 cc. per liter was sometimes harm- 

 ful, while 100 cc. per liter was toxic at all times. He later ('03) 

 reported 5 cc. toxic to Tinea. See also Knauthe ('07, p. 125). 



A series of experiments including most of the species at hand 

 confirmed the results of these workers with carbon dioxide. An 

 Ameiurus was narcotized in 163 cc. of carbon dioxide per liter 

 with oxygen at 1 cc. per liter. In this case the fish was placed 

 in tap water and the amount of carbon dioxide present was 

 gradually increased until anaesthesia was produced. Individuals 

 of nearly all the species at hand were dropped into the water 

 with the gas content as just given. They were all greatly stimu- 

 lated at first, but lost correlation of movements in a few moments 

 and died in ten to fifteen minutes. 



