Seasonal movement of one Mekong giant catfish, Pangasianodon gigas, in relation to the environmental conditions of Mae Peum Reservoir, northern Thailand

Greater knowledge of the relationship between movement patterns of the target speeies and the environmental eonditions (e.g., temperature and dissolved oxygen) is needed for effeetive fisheries management and eonservation (BRILL 1994, CARTAMIL & LOWE 2004). The Mekong giant eatfish Pangasianodon gigas is one of the largest freshwater fishes in the world, measuring up to 3 m in length and weighing in exeess of 300 kg. The eatfish is one o f the most important fisheries speeies ofthe Mekong River Basin in the Southeast Asia; however, the eateh number of wild eatfish in the Mekong River has deelined due to development o f the river and over-fishing (HOGAN 2004) and the eatfish eurrently is listed in CITES Appendix I and on the IUCN Red List of threatened speeies as a Critieally Endangered Speeies. Hatehery-reared juvenile and young immature eatfish were released into lakes and reservoirs as well as the Mekong River to enhanee the stoek (MEYNELL 2003). The behavior, movement patterns, and survival rate of these eatfish after release into natural eonditions remains largely unknown (MEYNELL 2003), although that information is quite useful for fishery management and eonservation deeision making (LOWE et al. 2003, HUMSTON et al. 2005). W e started to investiga te the movementpatterns ofthe eatfish using aeoustie telemetry in 2001 (ARAI et al. 2005). To assess the movement patterns ofthe eatfish during the rainy season in 2003, 8 fish tagged with aeoustie transmitters were released in Mae Peum reservoir, northern Thailand in 2003 (MITAMURA et al. 2008). Although 7 of 8 tagged fish had expelled the transmitters duringthe study period (8 -136 days ), the remaining one fish was monitored for more than 14 mo during both the dry and rainy seasons, whieh provided the movement patterns in relation to the seasonal environmental eondition. There are not so many studies that eontinuously monitored the same fish over a year due to the same diffieulties, sueh as fish mobility, vastness ofthe study si te, an d transmitter detaehment (LucAs 1989). The objeetive ofthis study was to report the seasonal movements of one eatfish in relation to environmental eonditions.