Thavee Viputhanumas

Horizontal and vertical movement of Mekong giant catfish Pangasianodon gigas measured using acoustic telemetry in Mae Peum Reservoir, Thailand

The horizontal and vertical movements of eight immature hatchery-reared Mekong giant catfish Pangasianodon gigas were monitored using acoustic telemetry in Mae Peum Reservoir, Thailand between 2003 and 2004. The fish were monitored for between eight days and more than 9 months. All of the fish moved over the entire reservoir within approximately 40 days after release. Subsequently, the home range became small approximately 40 days after release. The fish preferred deep areas in the reservoir. The fish displayed diel horizontal and vertical movement patterns. The fish showed larger-scale horizontal movement during the daytime than at night. The fish repeatedly showed active vertical movement during the day, whilst there was little variation in swimming depth at night. Our results imply that the vertical movements of the fish were related to the environmental condition of the reservoir.

Comparison of Two Methods of Attaching Telemetry Transmitters to the Mekong Giant Catfish, Pangasianodon gigas

Abstract For conservation and successful stock enhancement of endangered species, an understanding of the movement patterns and behavior of the target species is indispensable. The Mekong giant catfish, Pangasianodon gigas, is endemic to the Mekong Basin and now is threatened with extinction. Although biotelemetry using acoustic transmitters and receivers is expected to reveal its movement patterns and behavior, the most suitable attachment method for the transmitter to the catfish is unknown. In this study we examined the effects of external attachment and surgical implantation on the survival and growth of the catfish, compared with those in control individuals, in an earthen fish pond for approximately 2 months. No fish died during the experimental period. Furthermore, we found no fungal infections in any fish and no significant differences in growth rate among treatment and control fish. However, all transmitters of externally tagged fish were lost during the experimental period. In contrast, transmitters of some surgically implanted fish remained in the peritoneal cavity. In conclusion, the surgical implantation technique is suitable for long-term monitoring of the catfish.

Movements of immature hatchery-reared Mekong giant catfish Pangasianodon gigas released in the Mekong River, measured using acoustic telemetry

Twenty-eight immature hatchery-reared Mekong giant catfish Pangasianodon gigas tagged with acoustic transmitters were released in the Mekong River, Thailand from 2002 to 2004. Twenty-four and four fish were tagged with normal transmitters and pressure-sensitive transmitters, respectively. Five to seven automated monitoring receivers were used for monitoring the post-release movements. The tagged catfish could be detected for up to 97 days, the first detection taking place at the release point, where the fish remained for several days. Sixteen tagged fish (57%) were not detected at any later point. These fish may have passed along the opposite (Laos) side of the river without notice because the width of the river was larger than the detection range of the transmitter. The remaining 12 tagged fish (43%) could be detected by the receivers installed, excluding the release point receiver. Of these 12 tagged fish, six showed long-distance (30–80 km) upstream movements and one long-distance (50 km) downstream movement. These seven fish (25%) were detected only during the daytime, suggesting that the Mekong giant catfish is diurnal.

Vertical Movements of a Mekong Giant Catfish (Pangasianodon gigas) in Mae Peum Reservoir, Northern Thailand, Monitored by a Multi-Sensor Micro Data Logger

Abstract The vertical movements of one Mekong giant catfish Pangasianodon gigas were monitored for 3 days in August 2004 using a depth-temperature micro data logger. The logger was recovered using an innovative time-scheduled release system and located by searching for VHF radio signals. The logger was found approximately 2.2 km away from the release point and provided (n=705,128) depth and temperature data collected over a period of 98 hours following the release. The fish spent more than 99% of its time at less than 3 m below the surface. The maximum swimming depth was 5.6 m. No sharp thermocline was present during the experiment. Temperature did not have any detectable effect on the pattern of vertical movement of the fish. The dissolved oxygen concentration (DO) was stratified, with a concentration of >60% saturation in the first 3 m below the surface falling to 10% saturation at depths lower than 4 m. This specific DO stratification was found to limit the vertical movement of the catfish.

Detection Range and Horizontal Accuracy of a Fine-Scale Positioning Telemetry System at Kaeng Krachan Reservoir, Thailand

We examined the detection range and the accuracy of fine-scale positioning using Vemco Positioning System (VPS) for understanding the habitat use of Mekong giant catfish at Kaeng Krachan reservoir, Thailand. The appropriate distance between receivers and sound pressure of transmitters for the VPS was determined from the detection range test. We deployed 24 receivers at 500 m distance for the VPS positioning. The positioning accuracy was estimated using the stationary transmitters at fixed locations in the VPS array. The positions of the stationary transmitters were measured accurately (< 15 m). These results suggest that the VPS positioning can be useful for investigating fine-scale habitat use of Mekong giant catfish.

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.