THE EFFECT OF TEMPERATURE ON THE RATE OF DISAPPEARANCE OF CAUDAL BANDS IN FUNDULUS HETEROCLITUS

¹ Department of Zoology, University of Minnesota, and the Marine Biological Laboratory, Woods Hole

1. In Fundulus heteroclitus, the time required for the blanching of caudal bands of equal width varies greatly among different individuals under the same environmental conditions.

2. Each fish manifests a characteristic reaction time, however, and it is there fore possible, by performing "paired" experiments, to determine the effect of certain variable factors upon the rate of the blanching reaction in any individual.

3. By this method it has been found that the rate of blanching of caudal bands in Fundulus is directly influenced by temperature. A rise of 10° over the interval of 15° to 25° C. increased the speed of the reaction by an average of 3.04 ± 0.285 times in a group of 17 fish with one-ray bands. A similar rise over the interval of 20° to 30° C. increased it by an average of 2.18 ± 0.166 times in a group of 14 animals with one-ray bands, and 2.09 ± 0.16 times in seven animals with two-ray bands. Conversely, a decrease from 30° to 20° C. decreased the rate by an average of 2.59 ± 0.14 times in a group of 23 fish with one-ray bands.

It is suggested that these results be ascribed to the net effect of temperature upon the rate of the blanching reaction as a whole rather than to its influence upon any single process involved.

4. By the same method it was also found that the rate of blanching of caudal bands in fresh water is the same as that required in sea water. For a group of 8 animals with one-ray bands, the mean difference in reaction time in these two media at 30° C. was 0.44 ± 0.63 hours.