190 



BULLETIN OF THE BUREAU OF FISHERIES 



temperatures, indicative of increased respiratory metabolism (Gardner and Leetham, 

 1914 and 1914a; Rubner, 1924), was followed by a return to nearly normal breathing 

 as the fishes became adjusted to their new environment. This suggests that acclimati- 

 zation involves either an increase in the ability of fishes to absorb dissolved oxygen, 

 or a decrease in metabolic rate, such as was observed by Miss Behre (1918) in Planaria. 

 Experiments to test the latter possibility are now in progress. 



SUMMARY 



1. The maximum temperatures tolerated for 24 hours by normal animals belong- 

 ing to five different species were found to be as follows: Perch, 29.6° C. (85.3° F.); 

 large-mouthed black bass, 32.2° C. (90° F.); bluegill, 34° C. (93.2° F.); sunfish, 

 34° C. (93.2° F.) ; toad tadpole, 36.3° C. (97.3° F.). For the most part the tolerance 

 limits of the different species are correlated with the temperatures to which they are 

 exposed in their normal habitats. 



2. Within each species individuals of different ages appeared to have about the 

 same limits of tolerance, except in the case of tadpoles, which underwent a marked 

 loss of resistance during the later stages of metamorphosis. 



3. Continued exposure to high or low temperatures progressively raised or lowered 

 the limit of tolerance of each species. 



4. The fishes that inhabit shallow water (bass, bluegill, and sunfish) underwent 

 a change of tolerance by acclimatization much more readily than the perch, which 

 is typically an inhabitant of deep, cool water. 



5. Some of the minor differences in tolerance and in modifiability of resistance 

 among the various species of fishes seem to be specific, showing no apparent correla- 

 tion with ecological factors. 



6. Toad tadpoles differed from the fishes studied, in that, while having a very 

 high limit of tolerance, their resistance to heat was reduced very slowly by exposure 

 to low temperature. 



BIBLIOGRAPHY 



Adeehold, R. 



1888. Beitrag zur Kenntniss richtender Krafte bei der Bewegung niederer Organismen. 

 Jena Zeitschrift, Vol. XXII, pp. 310-342. 

 Behre, Ellinor Helene. 



1918. An experimental study of acclimation to temperature in Planaria dorotocephala. Bio- 

 logical Bulletin of the Marine Biological Laboratory, Vol. XXXV, No. 5, November, 

 1918, pp. 277-317. Woods Hole, Mass. 

 Birge, Edward A., and Chancey Juday. 



1911. The inland lakes of Wisconsin. The dissolved gases of the water and their biological 

 significance. Wisconsin Geological and Natural History Survey, Bulletin No. XXII, 

 Scientific Series No. 7, xx+259 pp. Madison. 



Coker, R. E. 



1925. Observations of hydrogen-ion concentration and of fishes in waters tributary to the 

 Catawba River, N. C. (with supplemental observations in some waters of Cape Cod, 

 Mass.). Ecology, Vol. VI, 1925, pp. 52-65, 1 fig. Brooklyn. 

 Dallinger, W. H. 



1880. On a series of experiments made to determine the thermal death point of known monad 

 germs when the heat is endured in a fluid. Journal, Royal Microscopical Society, 

 Vol. Ill, pp. 1-16. London. 



