58 ILLINOIS ACADEMY OF SCIENCE 



paper (Wells, '13) and will not be taken up here. If fishes 

 can detect and will react to so small a variation in the temper- 

 ature of the surrounding water as 1° C, it must be that they 

 are continually reacting to this factor in all fish environments 

 for such small differences in temperature must exist even in 

 the smallest body of water. It has been suggested that tempera- 

 ture has much to do with the migrations of salt water fishes 

 into fresh water streams, and the reaction experiments here 

 outlined furnish support for such an idea. We must not attempt 

 to limit the accuracy of such migrations to the temperature 

 factor, however, for there are many other factors to be con- 

 sidered. Undoubtedly density, salinity, gaseous content, and 

 acidity, as well as temperature, play their part in this phenom- 

 enon. The final solution of the problem must take all factors 

 into consideration. 



Summary: 1. The resistance of fishes to temperature 

 varies with the species and with the size of the fish. Large fish 

 of a given species are more resistant to high temperatures 

 than small fish of the same species, but the small fish adjust 

 to sudden changes from warm to cold more successfully. 



2. There is no definite maximum temperature for a given 

 species of fishes ; the maximum varies with the rate of heating, 

 with the size of the fish and with its physiological condition. 



3. Fishes detect and react to exceedingly small (.1° C.) 

 variations, in the temperature of the surrounding water. 



4. Both the resistance and the reaction experiments indi- 

 cate that the fishes experimented upon, possess a temperature 

 regulating mechanism which is much more delicate than that 

 of the warmer animals, though not as efficient in maintaining 

 a constant body temperature. 



5. The effect of temperature upon the migrations and dis- 

 tribution of fishes is obvious, since variations in temperature, 

 far in excess of the minimum variation to which fish will 

 react, are known to occur constantly in fish environments. 



ACKNOWLEDGMENTS AND BIBLIOGRAPHY 



I am indebted to Dr. V. E. Shelford for suggestions during the 

 preparation of this paper. 



Baird, Spencer F., 188 6. The Sea Fisheries of Eastern North 

 America. U. S. F. C. Report, 188 6. 



Bumpus, Hermon C, 1898. The reappearance of the Tile Fish. 

 U. S. F. C. Bull. 1898. 



Carter, August W., 1887. Temperature in Relation to Fish. 

 Nature, Vol. 36, p. 213. 



