REACTION AND RESISTANCE OF FISHES. 23! 



IV. PRESENTATION OF DATA. 



The following experiments show the effect of different degrees 

 of acidity and alkalinity, upon the reactions and longevity of 

 fresh water fishes. 



A. REACTIONS OF FISHES TO ACIDITY AND ALKALINITY. 

 i. Reaction to Acids. 



(a) To Carbonic Acid. A number of experiments was run 

 to determine the reactions of the fishes to this acid. Three 

 degrees of acidity were used for the most part: (i) Neutral, to 

 very faintly acid (aerated water) (2) moderately acid (8-10 c.c. 

 CO 2 per liter; obtained by using half and half mixture of I and 

 3); (3) strongly acid water (unaerated tap; 18 c.c. CO 2 per liter). 



(1) Moderately Acid Water vs. Strongly Acid Water (Graph i, 

 Chart /.). The fishes selected the lower acidity with much 

 precision. They also spent much time at the surface, as is 

 characteristic when the concentration of CO 2 is high. 



(2) Slightly Acid vs. Moderately Acid Water (Graph 2, Chart /.). 

 -The fishes were left in the tank, and the flow altered so that the 



moderately acid water ran into the end that had previously been 

 strongly acid and neutral water was run into the opposite end. 

 The fishes were graphed after five minutes. They definitely se- 

 lected the end of the tank into which the neutral water was 

 flowing. Test showed this end to contain 3 c.c. CO 2 per liter. 

 Seven experiments with this combination were run and all gave 

 similar results. Variations were due to specific and size dif- 

 ferences. The larger fishes and the crappies and green spotted 

 sunfishes selected a somewhat higher acidity than the smaller 

 fishes, especially the blue-gills. 



(3) 6 c.c. COz per Liter vs. 4 c.c. per Liter (Graph j, Chart /). 

 The concentrations of CO 2 were obtained by regulating the 

 amounts of aerated and unaerated water. Six experiments were 

 run. The bullheads and blue-gills selected the lower concen- 

 tration with precision, w r hile the sunfishes and crappies chose 

 the higher end with as much definiteness. Thus, as was seen 

 in (2), the species differ in the optimum CO 2 concentration 

 which they select at this time of year. 1 The difference in 



1 Because of the fact that the resistance of fishes varies with the season (Wells, 

 '14), it is very probable that the COs concentration selected by a given species will 

 show seasonal variations also. This point is yet to be investigated. 



