Effects of Water Temperature on Fish 45 



roughly similar to that of the soils of the lake bottom and the surrounding 

 basin. 



Fish are able to live in water having a pi I range from about 6 to 9 or 10. 

 Aldiough most natural waters do not eontain ehemieals in eoneentrations 

 great enough to limit the survival of fish, according to Neess,--^ at pH 5.5, 

 fish develop hypersensitivity to bacterial parasites and usually die within 

 a short time if the pH is as low as, or lower than 4.5. 



Moreover, very hard waters are sometimes toxic to fish. New clear 

 ponds, in regions where surface waters are hard, may show an upper pH 

 range of 10 or more when, in bright sunlight, their submerged plants or 

 algae are active in photosynthesis. These plants use up all of the free 

 carbon dioxide in die water and as much bicarbonate as is available to 

 them, wdth the result that maximum alkalinity is attained which, if high 

 enough, will cause the death of fish. In older ponds an accumulation of 

 organic matter acts as a buffering agent against high pH. 



Sulfates in newly flooded stripmine ponds often cause them to be acid. 

 If the stripmine is in a region where surface and ground waters are hard, 

 an accumulation of calcium and magnesium and organic material may 

 counteract the acidity so that these waters will eventually support fish and 

 other aquatic organisms. For example. Sigmoid Pond in Kickapoo State 

 Park, a former stripmine area located in central Illinois, contained 1340 

 ppm of sulfate on May 18, 1938 (an analysis by Illinois State Water 

 Survey, unpublished). This pond had a total hardness of 669 ppm, and 

 contained largemouth bass, crappies, bluegills, and green sunfish. The 

 pH ranged between 8 and 9. 



Occasionally, flowing wells and springs contain high amounts of iron 

 and sulfate, as well as methane and other gases that may make them 

 uninhabitable by fish. Usually, however, the exposure of such waters to 

 sunlight and aeration allows the precipitation of certain mineral elements 

 and the release of gases. 



EFFECTS OF WATER TEMPERATURE ON FISH 



Temperature plays an important role in the aquatic environment in 

 that certain organisms, including fish, are sensitive to the limitations of 

 the natural range of water temperatures. In a broad sense, fresh- water fish 

 can be separated into cold- or warm-water species. Ordinarily, one thinks 

 of the trout as being representative of the cold-water species and accord- 

 ing to James, Meehean, and Douglass, ^'^ rainbow and brook trout thrive 

 in water with a maximum summer temperature approximating 70°F. 

 Under certain conditions diey may tolerate higher temperatures for short 

 periods of time, and in this the rainbow trout is more resistant than the 



