REACTION AND RESISTANCE OF FISHES. 239 



that in open tanks the amount of CQz at the surface is markedly 

 less than at deeper levels. 



3. Conclusions Drawn from the Reaction Experiments. 



The reaction experiments recorded in the previous pages sug- 

 gest the following conclusions. (i) Fresh-water fishes are 

 negative to neutrality in favor of either slight acidity or slight 

 alkalinity. Their normal choice is slight acidity' (about .00005 N 

 H 2 SO 4 or .0001 N CO 2 ). (2) Species of fishes differ in the de- 

 gree of acidity selected. Blue-gills select water that is but 

 very slightly acid (1-2 c.c. CC>2 per liter, i. e., .0001 N carbonic 

 acid) while crappies select a concentration of from 4-6 c.c. CO? 

 per liter. (3) The principal stimuli to which fishes react are 

 H and OH ions. They do not react to ammonia, as a gas in 

 solution. 



B. RESISTANCE EXPERIMENTS. 



It has been pointed out that the stock of fishes did not live 

 well in the aquaria when these were supplied with water, which 

 was neutral, or nearly so; to determine more exactly the reasons 

 for the high mortality, between 50 and 60 experiments were 

 performed. Some of these experiments lasted through a number 

 of weeks, while others were finished in a few hours. The fishes 

 were placed in different concentrations of acid and alkali in 

 partly aerated w r ater (from the aquaria) and in distilled water. 



i. Resistance to Acids. 



The resistance of fishes to carbonic acid has been worked out 

 (Wells, '13) and it was decided to try the effects of other acids. 

 Ten experiments with sulfuric acid in distilled water are sum- 

 marized in Table III. The table shows that there is a concentra- 



TABLE III. 



SHOWING THE RESISTANCE OF FISHES (3 GRAM BLUE-GILLS) TO HiSO4 IN DISTILLED 



WATER. 



Concentration of Acid. Dying Time in Hours. 



.001 N 3.5 



.0005 N 7.0 



.0002 N 42.0 



.00015 N 60.0 



.000075 ^ Alive and vigorous at end of a month. 



