COLD DEATH IN THE GUPPY

¹ Department of Physiology, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania

A. Observations concerning both "primary chill coma" and "secondary chill coma"

1. In guppies acclimated to 23 to 30° C., exposures to temperatures below 10° C. produced "primary chill coma" while exposures to lethal temperatures above 10° C. caused "secondary chill coma."

2. The duration of a cold exposure at a specific temperature is the decisive lethal determinamut rather than the chilling temperature per se. An increase in the duration of a cold exposure causes an increase in mortality.

3. Tolerance to a cold exposure is inversely related to acclimation temperature. Tolerance to oxygen lack at normal temperatures also is inversely related to acclimation temperature.

4. Males are less cold-tolerant than females in the temperature range of "primary chill coma." There does not seem to be a sexual difference in cold tolerance in the temperature range of "secondary chill coma."

5. Young guppies (6-18 mg.) are less cold-tolerant than adults (80-900 mg.).

B. Observations on "primary chill coma"

1. Respiration did not return in any fish subjected to approximately three or more times the LD50 cold exposure, despite the fact that the circulation returned in all fish subjected to approximately twelve times the LD50 exposure or less.

2. The lethality of a cold exposure was increased by decreased oxygen before or during the exposure.

3. The lethality of a cold exposure was decreased by prior anesthesia with 1% urethan, increased oxygen during or after the exposure, or with two sequential cold exposures by exposing the fish to the less extreme temperature first.

4. The lethality of a cold exposure was unaltered by increased oxygen before the exposure, decreased oxygen (of a duration which was not lethal of itself) after the exposure, increased tonicity of the chilling water, or equilibrating the chilling water with 5% CO₂.

C. Observations on "secondary chill coma"

1. The lethality of a cold exposure was unaltered by increased oxygen during the exposure, or by the use of isotonic sodium chloride as the chilling medium.

D. The following conclusions may be drawn from the observations made:

1. Death due to "primary chill coma" in the guppy may be due to anoxic damage to a cold-depressed respiratory center.

2. The lethal effect of "primary chill coma" is related to the profoundness of respiratory depression and by the degree of depletion of the fish's oxygen reserve.

3. Osmoregulative failure does not seem to be a cause of death in "secondary chill coma" in the guppy.

4. Oxygen lack is not a lethal determinant in "secondary chill coma" in the guppy.