174 



BULLETIN OF THE BUREAU OF FISHERIES 



32 c 



1 min 



4 min 

 15 min. 



1 hr. 



4 hrs 

 24 hrs 



□ 



temperatures were wooden tubs, each large enough to hold four or five of the battery 

 jars containing the specimens. An electric heating unit was placed in the bottom, so 

 that stratification of the water was prevented almost entirely by the convection 

 currents; and the temperature was controlled by a mercury thermostat, which 

 operated a relay in the heating circuit. The aeration system was not needed in the 

 work on tadpoles but was essential for the fishes, because the limited capacity of 



the constant-temperature baths and the need of 

 testing separately a large number of individuals 

 necessitated the use of rather small jars for the 

 specimens. Air at low pressure was supplied by 

 a specially designed suction pump, from which a 

 rubber tube led to each specimen jar, where a fine 

 glass tip delivered the bubbles in a stream that 

 was strong enough to stir the water well. At or 

 below room temperature this system normally fur- 

 nished ample aeration, the respiration of the fishes 

 apparently being normal. 



"25° ~50~ 



7 individuals 



75 100% 

 (4 trials) 



340 



1 min. 



4 min. 

 15 min. 



1 hr. 



4 hrs. 

 24 hrs. 



SB 



25 50 

 15 individuals 



75 100$ 

 (9 trials) 



36° 



1 min. 



4 min. 

 15 min. 



1 hr. 



4 hrs.! 

 24 hrs. 



100% 



ACCLIMATIZATION CONDITIONS 



Acclimatization was carried on in battery jars, 

 different sizes being used, according to the size and 

 number of the specimens. Tadpoles were run in 

 lots of 10 to 20 without artificial aeration; fishes, 

 in lots of 1 to 4 with aeration. In all cases the jars 

 used were large enough, so that the fishes could turn 

 around without touching the sides of the vessel. 

 All specimens were fed during the acclimatization 

 periods. 



TEST CONDITIONS 



Lake Mendota water, drawn from the univer- 

 sity taps, was used in all the tests, being brought to 

 the desired temperature and then stirred vigorously 

 to remove excess air. Ordinarily, it was probably 

 just about saturated with oxygen at the beginning 

 of each experiment. 



The tests on the fishes were made in battery 

 jars, about 1,800 cubic centimeters of water being 

 used for yearling fishes and about 5 liters for the larger individuals. Tadpoles 

 usually were tested in groups of three in specimen jars containing 250 cubic centi- 

 meters of water. Transfers were made directly from the acclimatization tempera- 

 tures to the test temperatures, and there was no feeding during the 24-hour test 

 periods. 



DEGREE OF ACCURACY MAINTAINED 



Acclimatization periods listed as 24 hours include a few as low as 22 and a few as 

 high as 27 hours. The ordinary variation in the so-called 4-day periods was between 

 92 and 100 hours, while periods of from 15 to 17 days were included in the 16-day 



8 individuals (5 trials) 



Fig. 1.— Effects of high temperatures on "nor- 

 mal " large-mouthed black bass. The specimens 

 were transferred directly from room tempera- 

 ture to the test temperatures (32°, 34°, and 36°, 

 respectively). The six lines in each rectangle 

 represent successive observations on the same 

 individuals. The lengths of the sectors in each 

 line show the percentages of individuals that 

 were living or dead at the time of each observa- 

 tion. | ~| living; 3H 



I dead 



