LOSS AND GAIN OF HEAT-TOLERANCE BY THE CRAYFISH

¹ Department of Zoology, University of Cincinnati, and Stone Institute of Hydrobiology, The Ohio State University

1. Crayfish (Orconectes rusticus) taken from environmental temperatures between 22 and 26° lived for not more than six hours at 37° and for at least ten days at 35°. Their 12-hour and 24-hour median heat-tolerance limits were 36.4 and 35.6°, respectively.

2. Upon being transferred to about 4° and maintained at this temperature, their heat-tolerance, as measured by the 12-hour median tolerance limit, fell to 35.3° after four days, to 34.8° after eight days, to 34.1° after twelve days, and to 33.5° after sixteen days. Heat-tolerance was lost in a similar manner at about 12°, but more slowly.

3. The heat-tolerance lost after thirteen days of exposure to 4° was regained within one day after they had been returned to the original environmental temperature, the rate of gain of heat-tolerance being much higher than the rate of loss.

4. When tested after one week at 30°, the 24-hour median heat-tolerance limit had risen to 36.6° from the initial value of 35.6°. Two more weeks at 30° did not bring about a further increase in this tolerance limit, however.

5. Apparently the heat-tolerance of these crayfish was not affected by sex, size, or the stage of the molt cycle.

6. The results indicate that crayfish are among the more heat tolerant of the aquatic arthropods and fish for which appropriate data are available.

7. The similarities between the temperature relations of crayfish and fish suggest that the basic principles are alike in the two groups.