UPPER LETHAL TEMPERATURE RELATIONS OF THE GUPPY, LEBISTES RETICULATUS

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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.

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