A captive breeding program of the Siamese Narrow-headed Softshell Turtle, Chitra chitra Nutphand, 1986, the world’s largest softshell turtle and a critically endangered species, was conducted at Kanchanaburi Inland Fisheries Research and Development Center, Kanchanaburi Province, C. chitra laid eggs from February through April in artificial sandbanks. Each female produced up to 4 clutches/year with 40-88 eggs/clutch. Egg sizes (n=220) were 31.94±1.57 mm in width, 33.16±1.54 mm in length and 19.00±1.67 g in weight. The mean incubation time of C. chitra eggs was 59±3 days (n = 255) with a range of 55-65 days at 24-42 ℃ air temperature and 24-39 ℃ sand temperature. Hatchling sizes (n=297) were 38.46±1.52 mm in carapace width, 42.97±1.59 mm in carapace length and 13.10±1.03 g in weight. The hatching success in each clutch varied from 3 to 94 %. The hatchlings were fed with fry fishes of Labeo rohita and Oreochromis niloticus. After 14 weeks, the mean hatchling size was 86.70±5.17 mm in carapace width, 91.72±5.75 mm in carapace length and 103.97±18.08 g in weight. The survival rate of juveniles was 90.64%. Morphometric comparisons of skulls and carapaces of C. chitra and c. indica, based on 27 skull ratio characters and 53 carapace ratio characters, showed that there were clear osteological differences between Indian and Thai forms. The magnitude of the variation supports the argument that Thai animals warrant specific status. The eggshell structure of wild C. chitra was studied. The result of SEM showed that the eggshell had three layers; an outer calcareous sheet, a middle crystalline layer and an inner fibrous layer. The eggshells were composed of oxygen (52.96±4.81%), carbon (35.03±9.17%), magnesium (5.55±0.34%), calcium (5.37±7.16%), silica (2,87±1.64%), aluminum (2.30±1.07%), potassium (0.17±0.1%), and sodium (0.74±0.3%). The eggshell was the aragonite form of CaCO3. This study confirms that C. chitra still exists in the Mae Klong and Chao Phraya river systems but is very rare. Another species, C. burmanica Jaruthanin, 2002 or C. vandijki McCord & Pritchard, 2002, was found in the Salween river system during the survey. A new record of C. chitra in the Mae Ping River was also reported in this study. Due to the rapid decline of the natural population of C. chitra, the conservation management is urgently needed.
