Suitability of tropical river fishes for PIT tagging: Results for four Lower Mekong species

Tropical river systems support some of the most productive inland fisheries around the world, but their fisheries are being placed under growing pressure from disruptions to connectivity caused by river developments. Fish passage measures and complementary monitoring techniques are needed to mitigate the barrier impacts of river developments and validate the effectiveness of such measures, respectively. Passive integrated transponder (PIT) systems have been shown to be effective for monitoring the effectiveness of fish passage measures in temperate river systems but remain largely untested in tropical systems. The aim of this study was to investigate the suitability of four wild-caught tropical species from the Mekong River (Hypsibarbus lagleri, Hemibagrus filamentus, Barbonymus schwanenfeldii, and Scaphognathops bandanensis) to PIT tagging. This was achieved by undertaking PIT tag retention experiments in outdoor tanks onsite, to assess whether PIT tags can be retained in these species without impacting their survival and body condition. We found that there was no significant impact of PIT tagging on mortality; no fish lost condition from tagging; and the overall tag rejection rate was very low (4.5%) in all four species. The study findings indicate that H. lagleri, H. filamentus, B. schwanenfeldii, and S. bandanensis are all suitable for being PIT tagged in tropical river systems, and therefore could potentially be used to assess various fish passage metrics such as approach, attraction and passage efficiency.