Productive fisheries in the Lower Mekong Basin (LMB) are threatened by river development outcomes. One of the first dams, at Xayaburi, in Lao PDR, had significant investment to provide for fish passage in the final designs. The level of investment, and the complexity of the fish passage facilities, are unprecedented anywhere in the tropical or sub-tropical world. Nevertheless, the facilities need to be rigorously assessed to determine if they meet the design specifications. There are a wide range of mark-recapture techniques available for assessing fish movement patterns in and around dams. The use of passive integrated transponders (or PIT tags) has been widely accepted globally. PIT tagging has been found to be especially effective for examining the movement patterns of freshwater fish largely owing to the fact that the tags (1) are relatively inexpensive, (2) are powered electromagnetically and do not need a battery, and (3) can be applied to both large- and small-bodied fishes. The success of any PIT tagging system in a fish pass is highly dependent on a suitably configured PIT antenna system. PIT tags have never been applied in the Mekong before and there is no effective method for safely collecting fish for tagging studies (i.e. most efforts involve gill netting, which can lead to mortality). This presentation reports on a short research project which designed and assessed an antenna system for potential installation at the site and discusses the logistical process for the actual installation. Antenna design tests led to the establishment of a design that had sufficient read range and pings-per-second which were within the expected swim speed ranges of selected target species. The design was effectively installed in the field and performed well when tested in situ. It forms a template for considering the installation of PIT systems at other large tropical fishways.