UPPER LETHAL TEMPERATURE RELATIONS OF THE GUPPY, LEBISTES RETICULATUS

Abstract

Guppies, Lebistes reticulatus, of inbred and unselected stocks, were tested for their variability in resistance to upper lethal temperatures. Unselected fish were maintained in constant temperatures of 20°, 25°, and 30 °C. from birth and were subjected to lethal temperatures either without further treatment or acclimated to 30 °C. before testing. Inbred lines were reared at 25 °C. and acclimated to 30 °C. Resistance times were determined at constant temperatures ranging from 33° to 38 °C. Acclimation has a moderate influence on the resistance times at the higher lethal temperatures, but the effect is lessened at 35 °C. and disappears at 34 °C. There is an indication of an optimum rearing temperature in the neighborhood of 25 °C. for resistance to the higher temperatures. General response to high lethal temperatures is similar to that reported for other fish, but heterogeneity is exhibited at 37° and 34 °C. Both genetic composition and early thermal history influence resistance to high temperatures as well as acclimation just prior to experiment. The upper incipient lethal temperature is slightly above 32 °C. over the biokinetic range of the guppy.