REACTIONS OF FISHES TO ATMOSPHERIC GASES 221 



The fishes studied represent all degrees of gregariousness. The 

 Abramis, Hybopsis, and Notropis are strongly gregarious. While 

 they tend to follow any small fish, the most compact schools 

 are made up of fishes of about the same size. Fishes larger or 

 smaller than the majority are most likely to stray. Very com- 

 pact schools of different species may be maintained if the fishes 

 are about the same size. Lepomis, Ambloplites and Microp- 

 terus are only slightly gregarious in captivity, Lepomis least of 

 all. The Umbra and Ameiurus are least gregarious of the swim- 

 ming fishes, two fishes rarely moving together. Of the darting 

 and resting fishes, none are more than sUghtly gregarious. 



IV. THE PHYSIOLOGICAL EFFECT OF GASES UPON FISHES 



The physiological effects of gases upon fishes have been but 

 Uttle studied experimentally. Nothing has been done upon the 

 species of fish which we used in the gas gradient experiments. 

 ^Mlile not a part of our main problem, we considered a knowl- 

 edge of the effects of gases upon the species studied of impor- 

 tance and accordingly conducted some preliminary experiments. 

 Some typical results of these are included here. 



1. EFFECT OF A GREAT EXCESS OF NITROGEN AND OXYGEN 



As has already been stated, the laboratory water supply con- 

 tains an excess of gas at all times, this being especially true in 

 the w:inter and spring. Fish kept in water which contains a 

 large quantity of gas, usually develop gas bubble disease. Bub- 

 bles of gas, consisting largely of nitrogen (Marsh and Gorman '05) 

 collect in the fins, beneath the skin of the head, behind the eyes, 

 thus producing 'pop eye,' and in the circulatory system, espe- 

 cially in the heart, where they interfere with the circulation so 

 as to cause death. Hitherto, the disease has been noticed espe- 

 cially in marine fishes. 



Gas bubble disease developed in the stock of fishes during the 

 progress of the experiments. The excess gas in the aquarium 

 water ranged from 1 to 2 cc. per liter of both nitrogen and oxygen. 

 Gas bubbles developed in the fins of Ambloplites, Hybopsis, 



