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. [ABSTRACT FROM AUTHOR]