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3- DIFFICUI.TIES TO BE GUARDED AGAINST IN FISH EXPERIMENTS. 



a. Character of IVatcr. 



At the beginning of the work Dr. Wells ('15 and '15a) undertook 

 a careful study of the relation of fishes to salts, acids, and alkalies. 

 In general he found that carbonates do not have detrimental effects 

 upon fishes when the water is acid. He further found many minor 

 complications in connection with different salts which occur in some 

 waters but none of these occurred in the water used. His findings 

 relative to acidity, alkalinity, etc. are of general application and may 

 be summarized as follows: 



Water which is consistently slightly alkaline lessens the activity 

 of fishes and the mortality is high. N/ioo alkalinitv, KOH, (56 pts. 

 per m.) kills them in a few hours. 



Neutral water also seems to be toxic to the fishes, and they become 

 less and less active until death may occur. 



An optimum acidity is obvious. 2-6 cc. of CO^, per liter, (4-12 

 pts. per m.) seems to be the proper acid concentration for many fresh 

 water fishes. Higher concentrations prove fatal very soon, though 

 fishes will live for some time in 10-20 cc. per liter (20-40 pts. per m.) 

 of carbon dioxide. N/io,ooo H0SO4, (4.9 pts. per m.) is fatal in a 

 day or so, but N/20,000 H2SO4, (2.4 pts. per m.) seems to be near 

 their optimum as they live in this concentration for a long time. 



Fishes react very definitely to exceedingly small concentrations of 

 hydrogen and hydroxyl ions. Fresh-water fishes in a gradient which 

 is slightly acid at one end and neutral near the middle and slightly 

 alkaline at the other end will spend most of their time in the acid end, 

 turning back from the alkaline end at a point just on the acid side of 

 neutrality. The concentration here when tested shows that they turn 

 back when the acid concentration falls below N/ 12,000 carbonic acid 

 (3.5 pts. per m.). 



In a gradient where the fishes may select between alkalinity and 

 neutrality they avoid the neutral water to some extent and spend the 

 greater part of the time in slightly alkaline water. 



b. Quantity of Water. 



In the aquaria suckers, small-mouthed and large-mouthed black 

 bass died frequently when the flow of water was small and the depth 

 in the aquaria more than 6 inches. This was probably due to insuf- 

 ficient oxygen. When the amount of water in the aquaria was small 

 and the flow sluggish as was the case when the water was 2 or 3 inches 



