A New and Unique Species of Ricefish (Teleostei: Adrianichthyidae: Oryzias) from the Lariang River Basin, Sulawesi, Indonesia, and the First Known Sympatric Ricefish Species Pair from Sulawesi Rivers

A majority of ichthyological research on Sulawesi is focused on the island's ancient lakes, whereas many, even large, river systems remain unstudied. This is particularly true for the Lariang River in the central highlands of Sulawesi, the island's longest river with the largest drainage basin. Recent collection efforts there revealed a previously unknown species of ricefish (Teleostei: Adrianichthyidae: Oryzias), which is described herein. It is distinguished from its congeners by its high, non-overlapping scale count in lateral series. Interestingly, it occurs in sympatry with another recently described ricefish species. A phylogenetic analysis based on mitochondrial ND2 gene sequences recovered both species as sister lineages, making them the first known case of a riverine species pair in this family. The new species is further separated from its close relatives because it is a transfer-brooding species within a clade of pelvic-brooding species, suggesting a secondary reversal of reproductive modes. Possibly related to this, it also has the most pronounced rheophilic ecology of all known ricefish species. This discovery highlights the diversity of evolutionarily derived lineages found on Sulawesi and stresses the importance of additional explorative surveying to record it.