First record of Mastacembelus notophthalmus (Actinopterygii: Synbranchiformes: Mastacembelidae) for Belitung Island, Indonesia

This study was conducted aiming to record for the first time the occurrence of Mastacembelus notophthalmus Roberts, 1989 in Belitung Island (Indonesia), and update the geographic distribution of this species. Although this species is categorized as LC according to the IUCN Red List, it is rarely reported in fish inventories, with few specimens sampled. Moreover, data on the geographic distribution, population size, and other population details of M. notophthalmus are scarce and insufficient to predict possible threats and propose appropriate conservation measures and policies. A single specimen of Mastacembelus was collected using a fish trap on 20 February 2023, in a swamp, located in the middle course of the Lenggang River, Belitung Island, Indonesia. This specimen was identified as M. notophthalmus and this finding constitutes the southernmost record for this species, expanding its geographic range. In addition, the new record site is about 700 km south-east of the nearest locality in Peninsular Malaysia, about 250 km south-east of the nearest locality in Bangka Island, about 600 km south-east of the nearest locality in Sumatra, and about 500 km south-west from the nearest locality in Borneo. Better ecological and biological data concerning distribution, habitat, and stressors is crucial to reassess the conservation status of M. notophthalmus, and possible future conservation measures and policies. Therefore, we emphasize here the urgency for more comprehensive and accurate data to facilitate conservation assessments and management in Indonesia.