TOLERANCE OP HIGH TEMPERATURES BY PISHES, ETC. 



185 



BEHAVIOR AT HIGH TEMPERATURES 



Observations on the behavior and apparent condition of the experimental 

 animals, while difficult to reduce to quantitative terms, are of some interest because 

 they support, in some important respects, the conclusions drawn from the data on 

 survival, and they give some clues as to the nature of the acclimatization process. 

 Three effects commonly followed the transfer of normal fishes to high temperatures: 



1. Increase in general activity. 



2. Disturbances of equilibrium such as (a) elevation of the tail, so that the 

 body stood at an angle of from 30 to 90° to the horizontal; (&) a persistent tendency 

 of the fish to rise to the surface, tail first, constant use of the fins being required to 

 keep the fish at the bottom; (c) a rolling from side to side, or rotation on the longi- 

 tudinal axis; (d) floating at the surface. 



3. Increase of respiratory movements. Sometimes there was merely an increase 

 in respiratory rate, but in other cases there was also an increase in amplitude of 

 respiratory movements, so that breathing was labored, the fishes often coming to 

 the surface to gulp air. 



The disturbance of equilibrium usually occurred within 1 to 4 minutes after the 

 fishes were transferred to the higher temperature, although sometimes it was delayed 

 longer, while the increase in respiratory movements usually became pronounced 

 within the first 15 minutes of the test. In cases where the fishes survived the 24-hour 

 test, normal equilibrium usually was regained in from 1 to 4 hours, while the labored 

 breathing commonly disappeared in from 4 to 20 hours. The original rate of respira- 

 tory movements seldom, if ever, was regained during the 24-hour test period. 



The extent to which the effects described were manifested by normal fishes 

 varied greatly, according to the test temperatures, and the description that follows 

 represents the usual results in all the species except the perch. 



1. At the highest temperature that most of the normal individuals could tolerate 

 for 24 hours there was some disturbance of equilibrium and respiration, followed by 

 complete recovery. 



2. At a temperature that a minority of the individuals could survive there was 

 marked initial disturbance of equilibrium and respiration. This was followed by 

 complete recovery in some cases; in other cases equilibrium was regained tempo- 

 rarily, but death occurred several hours later; in still others there was no recovery. 



3. At a temperature that none of the individuals could survive there was great 

 disturbance of both equilibrium and respiration, with no signs of recovery except, 

 perhaps, temporary improvement in equilibrium. 



The behavior of perch resembled, in a general way, that of the three other 

 species, but their recovery of normal respiration was slower. A bass, when 

 placed at 32° C. (89.6° F.), or a bluegill or sunfish at 34° C. (93.2° F.), their respec- 

 tive limits of tolerance, usually resumed light, easy breathing within 10 to 12 hours; 

 while a perch placed at 30° C. (86° F.), its limit of tolerance, often would continue 

 noticeably labored respiratory movements for two or three days. These facts 

 apparently support the conclusion, previously reached, that the perch has the least 

 power of adjustment to increases in temperature of any of the fishes studied. 



The disturbances in equilibrium and respiration occurring within the first 15 

 minutes of a test are referred to as the "initial shock." Table 7 summarizes the 



