Preliminary study of the development of gonads, sex hormones and age of the Maekhong giant catfish (Pangasinodon gigas, Chevey) living in natural water

Since only 2 Giant Catfish were caught form the Maekhong River in the year 2000, this fish species might become extinct in the future. However, the young Giant Catfish can be produced by means of artificial reproduction and released into natural water such as at dams. This preliminary study here was conducted at Mae-ngad somboonchol Dam, Mae Kaung Udomthara Dam, and the Maekhong River. As the initial data, the growth of the fish caught at all stations showed a satisfactory rate. Nevertheless, no information about reproductive system, sex hormone and fish age was obtained. However, from this survey, some more informations was detected : the fish from Maekong River was 149 kg in the male and 247 kg in the female. The Gonadosomatic Index (GSI) were 2.2 percent and 11 percent in male and female, respectively. The sexual hormone testosterone (T) were 0.07 ng/ml and estradiol (E2) were 123 pg/ml. The age was about 21 years. The fish caught from Maengad dam during September-October 1999 showed an average weight of 156 kg and 164 kg in males and females, respectively. The GSI in males was 0.11 percent and 0.35 percent in females. The average age was about 13 years. The fish caught at the Maekuang Dam during January-February 2000, showed an average weight of 53 kg and 58 kg in males and females, respectively. The GSI was 0.05 percent in males and 0.11 percent in females. The average age was about 6 years. The sexual hormone content in fish from both dams was 0.02 ng/ml and 10 pg/ml of T and E2, respectively. Regarding the development of gonads, the fish from Mae-Ngad Dam was better than those from Mae-kuang Dam. However, the development stage was still in the initial stage and was unable to be used as brood stocks. The survey should be condcted through out the year at the dams in order to learn the development stage of the reproductive system. Consequently, we might select the mature stage fish from the dams for artificial reproduction at the right time instead of waiting for the fish from the Maekhong River.