Attempts had been made to select and develop a good strains of the Rana tigerina were based on the quantitative characteristics of parent stocks form various places. They were out-crossing by cross and reciprocal cross. Growth of the off springs (F[subscript 1]) were followed. It was found that the average weights of the froglets, 1-3 months old from spawning are 5.386 +- 0.565 gm., 22.624 +- 2.684 gm., and 42.367 +- 7.160 gm., respectively. Sexes can be identified at the age of 4-6 months. Males of 4, 5 and 6 month old, weighted 118.295 +- 19.575 gm., 125.60 +- 35.627 gm., and 128.537 +- 40.923 gm. respectively, while females of the same ages weighted 146.810 +- 19.078 gm., 192.275 +- 35.592 gm. and 205.020 +- 40.506 gm., respectively. The same procedure had been applied to the Rana catesbeiana. A certain group of the offsprings showing a good growth rate and was separated and prepared to be used as the next parent stocks. The average weights obtained from 1 to 6 months old Rana catesbeiana were 9.996 +- 0.793 gm., 25.816 +- 1.847 gm., 44.340 +- 3.133 gm., 161.530 +- 22.399 gm., 175.750 +- 20.519 gm. and 205.440 +- 23.498 gm., respectively. In the culturing plan for meat production, the comparison of growth rate between Rana tigerina and Rana catesbeiana was done. Results showed that the female Rana tigerina and the Rana catesbeiana (of both male and female) at the age of 4-6 months have almost the same growth rate reaching an approximate weight of 5-6 frogs per kilogram. Annual sex steroids profiles in adult female and male frogs, Rana tigerina and Rana catesbeiana were elucidated. Trunk blood plasma were collected monthly in the year 1994. Plasma testosterone (T) and estradiol 17 beta (E[subscript 2]) were determined by radioimmunoassay. Plasma T levels in both male and female Rana tigerina were elevated from March through October. The highest value in the male was 3,000 pmol/L in May and 1,500-1,800 pmol/L in the female during April-June. Plasma T levels were as low as 100 pmol/L during November-February in both sexes. Similar profile was found in E[subscript 2]) secretion in the female. Plasma T levels in both male and female bullfrogs were high throughout the year. The highest T levels in the male and female were 2,600 pmol/L in April and June, respectively. Plasma E[subscript 2] levels in the female bullfrog were 1,000-5,000 pmol/L throughout the year. Results obtained indicated that the Rana tigerina exhibits breeding seasonality while the bullfrog Rana catesbeiana seems to be lacking of breeding seasonality when they were kept in the same environment in Thailand.
