NOTES ON THE DISSOLVED CONTENT OF WATER IN ITS 



EFFECT UPON FISHES. 



By M. C. MARSH, 

 United States Bureau of Fisheries. 



NATURAL IMPURITIES IN WATER. 



Since fishes are confined to water as their natural habitat, and since water 

 strictly pure scarcely exists naturally upon the earth, they live habitually in 

 water containing a certain amount of foreign substance in solution — in other 

 words, in impure water. There is also nearly always some foreign matter held 

 mechanically. Since these so-called impurities may vary greatly in kind and 

 degree, the study of the reactions which take place between fishes and impure 

 waters of various nature can not fail to be of both theoretical interest and prac- 

 tical importance. 



It is profitable to inquire first whether these impurities are merely incidental 

 to the life of the fish as they are to the water, or are essential and necessary. 

 That air dissolved in the water is necessary to support fishes is a matter of com- 

 mon knowledge and observation, for they die quickly if the water is not aerated. 

 It may likewise readily be shown by experiment that water containing dissolved 

 air alone is not sufficient even though plenty of food is supplied. For this pur- 

 pose, 5 liters of water were distilled through glass apparatus. Contrary to what 

 seems the general impression, distilled water has considerable air dissolved, 

 even immediately after the distillation. A portion of this water from the receiv- 

 ing flask was tested for oxygen during the distillation and contained, at 15° C, 

 5.48 c. c. of oxygen per liter. Twelve quinnat salmon fry in the sac stage were 

 placed in the 5 liters of water in a glass jar, with a current of air in small bubbles 

 constantly passing to the bottom of the jar and bubbling up through the water. 

 A control was set in exactly the same way, save that Potomac tap water was used 

 instead of distilled water. Three and one-half hours after the beginning of the 

 experiment, the water in each jar being at 14° C, oxygen was determined. The 

 Potomac sample held 7.25 c. c. per liter, the distilled sample 7.09 c. c, each 

 therefore almost air-saturated with oxygen . In the distilled water, after 24 hours, 

 2 fry were dead, after 27 hours 3 fry, after 37^2 hours all were dead. All the fry 

 in the control remained alive. During the experiment the aeration of the con- 

 trol was never greater than that of the distilled sample, and was usually less. 



893 



