Morphological and genetic study describes new Acrossocheilus species in Hunan

A study combining anatomical measurements, DNA barcoding, species-delimitation analysis and mitochondrial genome sequencing formally described a new fish species, Acrossocheilus zhangjiajiensis, from the upper Lishui River in Zhangjiajie City, Hunan Province, China. The authors examined 11 specimens collected in Bamaoxi Village, Sangzhi County, between 2021 and 2024, and increased the number of recognized species in the genus to 25.

The researchers designated specimen JWS2024296, measuring 120.4 millimetres in standard length, as the holotype and deposited 10 paratypes collected at the same locality. The specimens were preserved in 85% ethanol and deposited in the Molecular Ecology Laboratory at Zhangjiajie Campus, Jishou University. Measurements were recorded with a digital caliper to the nearest 0.1 millimetre and expressed as percentages of standard length or head length, while vertebral counts for two specimens were examined by X-radiography.

The new species has an elongated, laterally compressed body, an inferior mouth, two pairs of barbels and a complete lateral line with 37 to 38 scales. Its diagnosis combines six vertical black bars on the flanks, which remain present through adulthood, with black markings on the dorsal-fin membranes, a slightly hardened last unbranched dorsal-fin ray with a smooth posterior margin, and a maxillary barbel extending to the midpoint of the eye. In living individuals, the bars are distinct in juveniles and become shorter and fainter in adults.

Morphological comparisons involved 11 A. zhangjiajiensis and 11 A. jishouensis specimens of comparable size. Although many measured ranges overlapped, Mann–Whitney U tests found significant differences in 11 of 26 characters at P ≤ 0.05, including eye diameter, rostral-barbel length, postdorsal length, dorsal-fin length, pelvic-fin length, pectoral-fin length, caudal-fin length and pelvic-to-anal distance. X-radiography also found 4+33 vertebrae in two new-species specimens, compared with 4+35 vertebrae in two A. jishouensis specimens examined in the study.

For the mitochondrial cytochrome oxidase I analysis, the researchers extracted DNA from fin tissue of three A. zhangjiajiensis individuals. The COI haplotype network identified two haplotypes in the new species and eight in 23 A. jishouensis individuals. The overall COI genetic distance between the two species was 3.1%, and the haplotype groups were clearly separated. Maximum-likelihood and Bayesian analyses based on both COI and 13 mitochondrial protein-coding genes placed the new species as the sister taxon of A. jishouensis.

The researchers also applied the Bayesian Poisson Tree Processes model to the COI tree. It identified 10 putative species groups among the Acrossocheilus species included in the analysis. The lineage containing A. zhangjiajiensis had a branch length of 0.063, above the model’s automatically estimated threshold of 0.034, and was treated as an independent group. This molecular analysis did not include every recognized species in the genus, so the reported species-delimitation result applies to the sampled taxa rather than providing a comprehensive revision of Acrossocheilus.

Analysis of the 13 protein-coding genes gave genetic distances of 3.3% between A. zhangjiajiensis and A. jishouensis and as much as 11.4% between the new species and A. longipinnis. Within the comparison with its closest sampled relative, the ND4L gene showed the lowest distance at 1.0%, while ND6 showed the highest at 6.6%. A Jinping, Guizhou, population assigned to A. jishouensis also showed divergence from other populations of that species, but the study retained its identification because no physical specimens were available for examination.

A separate specimen provided the first complete mitochondrial genome reported for A. zhangjiajiensis. The assembled sequence was 16,592 base pairs long and contained 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes and a D-loop region. The authors assembled and annotated the sequence, manually verified the annotation and deposited it in GenBank. The COI sequences and mitochondrial genome were likewise deposited as GenBank records PV200282–PV200284 and PV200285, respectively.

The description places A. zhangjiajiensis in the barred group, whose members bear vertical black bars. Its combination of coloration, barbel length, dorsal-fin anatomy, bar position and scale count distinguishes it from the other barred species examined by the authors, while molecular evidence separates it from A. jishouensis, a related species also recorded in Zhangjiajie but from a different drainage. At present, the new species is known only from the type locality in shallow, clear, gently flowing water with a gravel bottom in the upper reaches of the northern branch of the Lishui River.

Subject of Research: Integrative taxonomic description of a new Acrossocheilus fish species from Hunan, China

Article Title: Integrative taxonomy reveals a new species of Acrossocheilus ( Cypriniformes , Cyprinidae ) from Hunan Province, China

Article References: Cao, J., Deng, Z., Xiang, H., Xie, Y., Wang, C., Li, H., Hu, Y., Wei, Y., & Jiang, W. (2026). Integrative taxonomy reveals a new species of Acrossocheilus (Cypriniformes, Cyprinidae) from Hunan Province, China. Zoosystematics and Evolution, 102(3), 869-883. https://doi.org/10.3897/zse.102.195486

Image Credits: AI Generated

DOI: 10.3897/zse.102.195486

Keywords: Acrossocheilus, new species, fish taxonomy, integrative taxonomy, Hunan Province, Lishui River, species delimitation, mitochondrial genome, DNA barcoding, Integrative, taxonomy, reveals