Using fish swimming ability to refine criteria for fishway construction in Myanmar

The construction of dams and other river infrastructures is threatening migratory fish stocks in many parts of the world by greatly reducing river-floodplain connectivity. Fishways are technical tools that can restore river connectivity for migratory fishes, but their effectiveness is often limited by a lack of biological information on their target species, especially in developing countries of South East Asia. We sought to inform the design of a vertical-slot fishway for Myanmar migratory fishes, by using a flume-based vertical-slot fishway to determine if (1) their passage ability is influenced by hydraulic conditions (such as depth and head differential or ‘headloss’ between cells); and (2) fish size influences passage ability for each species. This was achieved by comparing passage success under headloss options of 50-mm and 100-mm, and by assessing the relationship between size and ability to pass the flume – in four representative migratory species: Pangasius pangasius (pangas catfish), Notopterus notopterus (featherback fish), Puntius chola (swamp barbs) and Esomus danrica (flying barbs). Our results indicated that flume passage ability was greater under the 50-mm headloss for Pangasius pangasius, Notopterus notopterus and Puntius chola; and that flume passage ability increased in larger individuals for Pangasius pangasius and Notopterus notopterus. In comparison, Esomus danrica could not ascend under either the 50-mm or 100-mm headloss options. The inter-specific variability in these results empirically demonstrates the importance of obtaining baseline biological information on the target species for planned fishways in order to optimise their effectiveness.