Abstract:
The aim of this study was to determine whether farm frogs in Thailand exhibited a breeding season. Annual profiles of testosterone levels in plasma and testis of adult male frogs (age between 12 18 months), Rana tigerina and Rana catesbeiana, were performed by radioimmunoassay. Plasma testosterone levels in Rana tigerina increased from March to October (1250.80 to 3182.00 p mol/L) higher than which were found during November to February (163.09 to 219.00 p mol/L) In contrast, testicular testosterone levels were found as low as 4.96 to 26.7 p mol/g during the period of February to November and increased dramatically to 50.17 to 102.07 p mol/g during November to January. Gonado-somatic index (GSI %) was found to be 0.13 to 0.23 % during March to October and 0.03 % to 0.08 % during November to January. Plasma testosterone levels in male Rana catesbeiana did not fluctuate throughout the year, the hormone levels were about 628.44 to 1834.44 p mol/L. The highest plasma level was found in April which was 2606.75±108.87 p mol/L. The similar unfluctuated profile was found in testicular testosterone levels and GSI% which were found to be 2.30 to 5.10 p mol/g and 0.09% to 0.16% respectively (the highest testicular testosterone level was found only in May which was 8.88 ± 0.90 p mol/g). The results indicate that in the same environment, Rana tigerina seems to exhibit a breeding season while Rana catesbeiana exhibit the lack of a breeding season.