Mekong Giant Catfish Tracking Project

Mekong giant catfish Pangasianodon gigas is endemic to the Mekong River. The catfish is one of the largest freshwater fish in the world, measuring up to 3 m in length and weighing in excess of 300 kg. Historically, the catfish was distributed throughout the Mekong River basin from Yunnan Provice, China to Vietnam. Currently, the catfish seems to be limited to the Mekong River and its tributaries in Thailand, Laos and Cambodia. In Thailand, the number of the wild catfish captured in the Mekong River has decreased due to the development of the Mekong River and indiscriminate fishing these days. Therefore, ecological researches are urgently necessary to conserve the catfish. The objective of this study was to clarify the migratory behavior of the Mekong giant catfish in the Mekong River cooperated with the Department of Fisheries, Thai government.

We used an ultrasonic coded transmitter (V16-4H, Vemco Co. Ltd., Canada) that was 16 mm in diameter, 65mm long, and weighed 10 g in water. The transmitter was used to transmit complex codes of up to six pulses. We can identify up to 256 different fishes on the same frequency.
   The VR1 receiver system (Vemco Co. Ltd., Canada) was able to record attendance of tagged fish with coded transmitter. The dimension was 60 mm in diameter with 205 mm length. This receiver was installed in the place at a middle water depth where the tagged fish pass through in advance. The ID number, the date and time were recorded when the tagged fish passed within 200-300 m of the receiver.
Ten sample Mekong Giant Catfish Pangasianodon gigas that were artificial catfish reared in the Karasin Freshwater Research Station, DOF in Karasin prefecture were used for the release experiment. The catfish were released on 27 June 2002. The release point was the mouse of the Song Khram River which was one of the branches of the Mekong River in Nakhon Phanom prefecture. We will release more ten catfish on May 2003, covering over a thousand kilometer from Chaing Khong to Khnog Chiam.

In this study, we found that the Mekong giant catfish tended to migrate upward in the Mekong River. However, the important questions, gwhy do they migrate upward?h and gDoes the wild Mekong giant catfish also migrate upward?h remain to be answered.