TOLERANCE OF HIGH TEMPERATURES BY FISHES, ETC. 



183 



RESULTS OF EXPERIMENTS ON FISHES 



Temperatures tolerated for 24 hours. 



32 



34 



B 



Perch 



Bass 



The facts regarding fishes shown in Figure 9 may be summarized as follows: 

 (1) The loss in tolerance by acclimatization at 10° C. was most rapid in sunfishes and 

 hluegills, the species that have the highest normal resistance ; it was less marked in 

 the bass, and was decidedly the least in the perch, which has the lowest normal toler- 

 ance. (2) The gain in tolerance at 

 30° C. was rapid in the bass and 

 relatively slow in the sunfishes, 

 bluegills, and perch. 



Four facts regarding the data 

 on which these conclusions are based 

 may be noted : (1) With a few excep- 

 tions (probably due to experimental 

 error), the results indicate a con- 

 tinuous increase in tolerance by 

 acclimatization at 30° C. and a 

 continuous decrease at 10° C. (2) 

 The tolerance limits determined for 

 the different periods of time (24 

 hours, 4 hours, 1 hour, 15 minutes, 

 and 4 minutes), involving, as they 

 do, more than one set of individuals 

 and more than one set of experi- 

 mental conditions, serve as a check 

 on each other and for the most part 

 corroborate each other. (3) The 

 percentage of results that are far off 

 from the mode in any series is small. 

 (4) Observations on behavior (which 

 will be presented later), although 

 hard to express in numerical terms, 

 support the conclusions. 



Inasmuch as the initial toler- 

 ance of bluegills and sunfishes was 

 relatively high (34° C; 93.2° F.) 

 and their gain in tolerance by acclimatization at 30° C. quite slow, it seemed possible 

 that their gain in tolerance was slow because the acclimatization temperature of 30° 

 was not high enough to evoke a vigorous reaction. This appeared the more probable 

 because Loeb and Wasteneys (1912) secured their greatest changes in tolerance by 

 exposing fishes, for short periods of time, to very high temperatures; so it was thought 

 desirable to determine the effect of acclimatization at the tolerance limit of each 

 species. 



Aocllmati- 

 satioas. 



30° 1 day 

 10° 3. day 

 10° 4 days 



30° 4 days 

 30° 1 day 

 10° 1 day 

 10° 4 day6 

 10° 18 days 



30° 4 days 

 30° 1 day 

 10° 1 day 

 10° 4 days 

 10° 16 days 



30° 4 days 

 30° 1 day 

 10° 1 day 

 10° 4 days 

 10° 16 days 



30° 4 days 

 30° 1 day 

 10° 1 day 

 10° 4 days 



BlueglU 



Sunflsh 



Toad tadpole 



Fig. 9. — Extent to which acclimatization alters the tolerance of each 

 species. The center line in each figure indicates the average tolerance 

 limit of "normal" individuals. The lengths of the bars extending to 

 the right show the average amounts of increase in tolerance produced 

 by acclimatization; those to the left show decreases 



