SELECTION RESPONSE ON THERMAL-RESISTANCE OF THE GUPPY POECILIA-RETICULATA

To elucidate the genetic control for thermal resistance of the guppy, its response to high temperature was measured as the death time, at which the immature fish acclimated at 23 degrees C died when exposed to 37 degrees C. Using sub-population comparison, the heritability of thermal resistance was estimated at 0.183. The two-way selection for thermal resistance led to a significant difference of the death time of immature fish between the high temperature resistant population and the sensitive one. The resistant population showed a higher heterozygotic frequency at AAT-1* and PGM-1* locus than the sensitive population. This suggests a heterotic effect for thermal resistance and inbreeding depression for thermal sensitivity. Cross experiments confirmed heterosis for thermal resistance, supporting the above suggestion.