Fish assemblages and diversity in three tributaries of the Irrawaddy River in China: changes, threats and conservation perspectives

Incompletely known fish assemblages and species diversity are substantial obstacles in fish conservation, particularly when their aquatic habitats are under threat due to rapid human-induced changes. Fish assemblages and diversity in three tributaries of the upper Irrawaddy River in China (the Dulong, Daying and Ruili rivers) were examined based on field collections and literature resources. The newly compiled fish assemblage recorded 85 species (in 8 orders, 20 families and 51 genera) distributed in the upper Irrawaddy. The fish compositions in the Daying (67 species, 44 genera, 19 families, 7 orders) and Ruili rivers (65 species, 44 genera, 19 families, 8 orders) were more similar to each other and more speciose than that in the Dulong River (14 species, 10 genera, 4 families, 3 orders). Two indices of taxonomic diversity (the average taxonomic distinctness (Δ+), and the variation in taxonomic distinctness (Λ+)) were used to discriminate four collections spanning a ten-year period. A decrease in taxonomic diversity and an increase in unevenness of the fish assemblages were found in both the Daying River and Ruili rivers, which indicated that the impacts were accumulated gradually during this decade, when dams and the spread of non-native species were major threats. Comparatively speaking, the Dulong River is still in a near-natural state, and thus the fish community has experienced less disturbance. In situ conservation (nature reserves and tributary protection) and ex situ conservation (artificial propagation and release) should be combined and managed to promote fish conservation in the future.