Iridescent chub (Opsariichthys iridescens), an upstream river fish with gravel substrate from Southeast China

NEWS - Iridescent chub (Opsariichthys iridescens) from the Qiantang and Oujiang rivers in Zhejiang Province and adjacent Yangtze River tributaries to the Qiantang River was established as a new species based on its unique morphology and gene sequence divergence from all congeners and monophyly recovered in a Cyt b gene-based phylogenetic analysis.

Opsariichthys Bleeker, 1863, is a group of small cyprinid fishes endemic to East Asia that inhabit fast-flowing rivers or streams. The type species, Opsariichthys uncirostris Temminck & Schlegel 1846, was originally described in the genus Leuciscus Cuvier 1816. A phylogenetic study based on mitochondrial genomes in 2017 confirmed lateral bars as the main diagnostic feature of the opsariichthys group.

Opsariichthys is currently considered to include 14 valid species with 8 of them distributed throughout mainland China. Valid species in mainland China are O. acutipinnis Bleeker 1871, O. amurensis Berg 1932, O. bidens Günther 1873, O. chengtui Kimura 1934, O. evolans Jordan & Evermann 1902, O. hainanensis Nichols & Pope 1927, O. macrolepis Yang & Hwang and O. minutus Nichols 1926.

While examining specimens collected from Zhejiang Province and adjacent Yangtze tributaries to the Qiantang River, researchers found several specimens did not belong to any described species. Further morphological and molecular analyses supported that they belonged to a new species.

O. iridescens can be well distinguished by the absence of a distinct anterior notch on the upper lip (vs. the presence of a distinct deep anterior notch on the upper lip in O. uncirostris, O. amurensis, O. minutus, O. hainanensis, O. dienbienensis Nguyen & Nguyen 2000, O. songmaensis Nguyen & Nguyen 2000, O. acutipinnis, O. chengtui, O. macrolepis, O. kaopingensis Chen & Wu 2009, O. pachycephalus Günther 1868 and O. duchuunguyeni Huynh & Chen 2013).

The new species is also distinguished from conspecifics by 45-52 lateral line scales, 9-10 scales above lateral line, 18-21 pre-dorsal scales, 16-17 circum-peduncular scales and two rows of pharyngeal teeth. In adult males, the upper jaw extends to or slightly beyond the vertical anterior margin of the orbit, the pectoral fins extend to the pelvic fins, are nearly uniform (narrow, pale bar on the trunk, significantly widened on the caudal peduncle), the nuptial tubercles on the cheeks and the lower jaw are fused basally to form a plate.

O. iridescens lives in the upper reaches of rivers with moderate flow speeds and clear water with gravel and small to medium-sized boulders as the substrate. Iridescens is the Latin form of the word iridescent. The term refers to the unique body coloration that is brighter than other known species in the genus. The researchers propose the Chinese common name Hóng Cǎi Mǎ Kǒu Yú (虹彩马口鱼).

Based on this new classification, the researchers establish O. acutipinnis, O. evolans and O. macrolepis previously known as Zacco platypus as valid species of Opsariichthys. O. amurensis, O. minutus and O. hainanensis previously considered synonymous with O. bidens were also revalidated. O. chengtui and O. pachycephalus was moved from Zacco to Opsariichthys, while the status of O. bea (Nguyen 1987) and O. hieni (Nguyen 1987) remains uncertain.

Original research

Peng X, Zhou J-J, Gao H-D, Yang J-Q (2024). A new species of Opsariichthys (Teleostei, Cypriniformes, Xenocyprididae) from Southeast China. ZooKeys 1214: 15-34, DOI:10.3897/zookeys.1214.127532

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