REACTIONS OF FISHES TO ATMOSPHERIC GASES 245 



ment. The third, which first moved into the tap water, soon 

 joined' the other two fishes and all remained in the boiled water 

 for thirty-four minutes. Then all began moving back and forth 

 showing a time preference for the tap water but without turn- 

 ings or other characteristic activity. In experiment 3 (table 11), 

 on the other hand, all the fishes moved to the tap water end of 

 the tank at the beginning and remained four minutes except for 

 a single excursion into the gradient. After this time they began 

 to go into the boiled water but showed a marked time preference 

 for the tap water end. In the box experiments (p. 230) and else- 

 where, the boiled water decreased the activity of Ambloplites 

 so that if for any reason the fishes came to rest in the boiled 

 water for a time, their tendency to leave was decreased rather 

 than increased, as is usually the case. 



The darting fishes, Catostomus and Etheostoma, reacted to the 

 boiled water and in fact to all differences in water in a somewhat 

 different way from the swimming fishes. In the experiment the 

 reactions of the fishes were most erratic. All of their movements 

 were dartings and restings, accompanied by risings to the surface. 

 Catostomus gave ofT bubbles of air and in two or three cases 

 leaped out of the water. However, they finally worked out an 

 apparent preference for the tap water. 



Long experiments with five or ten minute readings were con- 

 ducted with most of the species. Since some of the fishes, such 

 as Abramis, often established an apparent preference for one 

 end or the other without testing both, it was thought advisable 

 to confine the fishes in the boiled water for a time to permit 

 them to become affected by the boiled water before the readings 

 began. While this later proved to be of little advantage and 

 often undesirable, it was continued to make the series uniform. 

 The results are shown in table 12, page 246. 



Notropis which reacted definitely in the closely observed ex- 

 periments (tables 11 and 15) here shows a decided preference 

 for the boiled water. The fishes began rising to the surface — 

 one of their very definite reactions to unsuitable water — and 

 kept this up throughout the experiment. They tend to move 

 about in circles near the same spot when giving this reaction and 



