Morphological Description and Molecular Identification of a Newly Recorded Curved-back Ricefish, Oryzias curvinotus (Nichols & Pope, 1927), from Western Taiwan and Lieyu Island

Morphological Description and Molecular Identification of a Newly Recorded Curved-back Ricefish, Oryzias curvinotus (Nichols & Pope, 1927), from Western Taiwan and Lieyu Island

The curved-back ricefish, Oryzias curvinotus (Nichols & Pope, 1927), is newly recorded in Taiwan, with specimens collected from the Puzi River in western Taiwan and from Lieyu Island, one of the 12 islands of Kinmen. Identification was based on morphological characters and molecular analysis of mitochondrial DNA COI sequences. Phylogenetic analysis in the present study revealed that samples from the Puzi River formed a unique haplotype, differing from other published haplotypes from China. In contrast, samples from Lieyu Island shared a haplotype identical to seven published COI sequences generated from voucher specimens from China. On the island of Taiwan, O. curvinotus is rather rare and currently known only from the Puzi River. However, a ricefish specimen collected in 1916 from the Dajia River in central Taiwan, originally identified as Oryzias latipes (CAS-SU 23115), was re-identified as Oryzias curvinotus based on diagnostic morphological features examined in this study. O. curvinotus is believed to have been widely distributed in western Taiwan in the early 20th century, but its populations have since declined, likely due to the invasion of mosquito fish first introduced to Taiwan in 1911. This study also updates the geographic distribution of O. curvinotus, with Lieyu Island representing its northernmost distribution and western Taiwan its easternmost limit worldwide.