A new species of Yunnanilus is described from the Nanpanjiang River, Yunnan, China. The new species, Yunnanilus polylepis, can be distinguished from other species of Yunnanilus by the following combination of characteristics: Processus dentiformis absent; eye diameter smaller than interorbital width; outer gill raker absent and 10 inner gill rakers on first gill arch; whole trunk covered by scales; nine branched dorsal-fin rays; 10 or 11 branched pectoral-fin rays; six branched pelvic-fin rays. Despite our phylogenetic analysis, which sheds light on the complex relationships among Yunnanilus species, the majority of Yunnanilus species are restricted to more localized environments and habitats. It is urgent to address the environmental threats that jeopardize their survival, especially given their generally restricted distribution.

Loach, mitochondrial gene, morphology, Nanpanjiang River, taxonomy

Species belonging to the genus Yunnanilus Nichols, 1925 are primarily found in lakes, marshes, and slow-flowing waters, exhibiting an affinity for karstic regions, particularly in the Yunnan and Sichuan provinces of China (Du et al. 2021). Kottelat and Chu (1988), who identified eight valid species and six previously undescribed species from the Yunnan Plateau. Subsequently, Yang and Chen (1995) divided the species of Yunnanilus into the Y. nigromaculatus and Y. pleurotaenia species groups based on the absence or presence of lateral line and cephalic lateral line canals, respectively. Prokofiev (2010) classified the family Nemacheilidae into five tribes, i.e., Lefuini, Nemacheilini, Triplophysini, Vaillantellini, and Yunnanilini. However, the monophyly of the Yunnanilini tribe was not supported in subsequent studies, with Du et al. (2021) and Luo et al. (2023) revising the classification of Yunnanilini using both morphological characteristics and molecular evidence, resulting in the placement of the Y. nigromaculatus group into Eonemachilus Berg, 1938, Y. pulcherrimus Yang, Chen & Lan, 2004 into Micronemacheilus Rendahl, 1944, Y. retrodorsalis (Lan, Yang & Chen, 1995) into Troglonectes Zhang & Zhao, 2016, and Y. jinxiensis Zhu, Du & Chen, 2009 into Paranemachilus Zhu, 1983. In addition, Du et al. (2023) delineated the phylogenetic relationships among Chinese nemacheilids possessing tube-shaped anterior nostrils, categorizing the spatial relationship between the anterior and posterior nostrils into three distinct types, i.e., separated, adjacent, and closely set. Within this framework, Du et al. (2023) described a new genus, Guinemachilus Du et al., 2023, into which Y. bailianensis Yang, 2013 and Y. longibarbatus Gan, Chen & Yang, 2007 were placed. Subsequently, He et al. (2024) described a new species, Yunnanilus Yangi He et al., 2024, from Nanpan Jiang based on morphological and molecular data. Currently, 19 species of Yunnanilus have been recognized, with diagnostic characters including inferior mouth, anterior and posterior nostrils separated, anterior nostril base tube-shaped and tip without elongated barbel-like structure, and lateral line and cephalic lateral-line canals present (Kottelat and Chu 1988; Du et al. 2021, 2023).

In November 2023, 13 Yunnanilus specimens were collected from a tributary of the Nanpanjiang River in Huaning County, Yuxi City, Yunnan Province, China. Based on morphological characteristics and molecular evidence, these specimens represent a previously undescribed species of Yunnanilus. Herein, we provide a description of the new species and its comparison to congeners.

All care and use of experimental animals complied with the relevant laws of the Chinese Laboratory of Animal Welfare and Ethics (GB/T 35892-2018). Specimens were rapidly euthanized by an overdose of anesthetic clove oil soon after being collected. Five specimens were preserved in 99% ethanol for molecular analyses, and eight specimens were stored in 10% formalin for morphological study. Specimens were deposited in the unming Natural History Museum of Zoology, Kunming Institute of Zoology (KIZ), Chinese Academy of Sciences (CAS).

All counts and measurements followed Kottelat (1990). The data were initially processed using Excel software for preliminary statistical analysis. Genomic DNA was extracted from fins fixed in ethanol. Partial sequences of the mitochondrial cytochrome c oxidase subunit I (COI) and cytochrome b (cyt b) were sequenced by Tsingke Biotechnology Co., Ltd. (China). All sequences were assembled by Seqman in the DNAstar software package and aligned in MEGA v11.0 (Tamura et al. 2021). Sequences have been submitted to GenBank (Accession Nos. PP254216–254236 for COI, PP262976–62996 for cyt b). The phylogenetic position of Yunnanilus polylepis sp. nov. was determined by maximum likelihood (ML) and Bayesian inference (BI) methods, which were implemented in the CIPRES Science Gateway (Miller et al. 2010). The ML was constructed in RAxML-HPC v8 (Stamatakis 2014). Selected was the rapid bootstrapping configuration, and the bootstrapping iterations were 1000. The BI tree was conducted by MrBayes in XSEDE v3.2.7a (Ronquist et al. 2012). Two runs were performed simultaneously with four Markov chains starting from a random tree. The chains were run for five million generations and sampled every 100 generations. The first 25% of sampled trees were discarded as burn-in, and the remaining trees were used to create a consensus tree and estimate Bayesian posterior probabilities (BPPs). The constructed phylogenetic trees were viewed and edited by FigTree v1.4.4 (Rambaut 2009).

Yunnanilus polylepis sp. nov. possesses typical characteristics of the genus Yunnanilus, including an inferior mouth, anterior and posterior nostrils separated, a tube-shaped base of anterior nostrils that is not elongated into a barbel-like structure, and lateral line and cephalic lateral-line canals present (Du et al. 2021, 2023).

To date, 20 species of Yunnanilus, including the newly described species, have been recorded from the Yunnan and Sichuan provinces. Among these species, 12 occur in the Nanpanjiang River (Y. analis Yang, 1990, Y. chui Yang, 1991, Y. elakatis Cao & Zhu, 1989, Y. forkicaudalis Li, 1999, Y. macrogaster Kottelat & Chu, 1988, Y. macrolepis Li, Tao & Mao, 2000, Y. macrositanus Li, 1999, Y. nanpanjiangensis Li, Tao & Lu, 1994, Y. paludosus Kottelat & Chu, 1988, Y. parvus Kottelat & Chu, 1988, Y. yangi He et al., 2024, and Yunnanilus polylepis sp. nov.), six occur in the Yangtze River (Y. discoloris Zhou & He, 1989, Y. jiuchiensis Du, Hou, Chen & Yang, 2018, Y. longibulla Yang, 1990, Y. pleurotaenia (Regan, 1904), Y. sichuanensis Ding, 1995, and Y. spanisbripes An, Liu & Li, 2009), and one species each occurs in the Beipanjiang (Y. beipanjiangensis Li, Mao & Sun, 1994) and Honghe rivers (Y. chuanheensis Jiang, Zhao, Du & Wang, 2021). Within the genus, Y. analis, Y. beipanjiangensis, Y. chui, Y. discoloris, Y. forkicaudalis, Y. paludosus, and Y. yangi are characterized by the absence of scales, while Y. elakatis, Y. macrositanus, and Y. nanpanjiangensis are characterized by scales exclusively present on the caudal peduncle. Although Yunnanilus polylepis sp. nov., Y. chuanheensis, Y. jiuchiensis, Y. longibulla, Y. macrogaster, Y. macrolepis, Y. parvus, Y. pleurotaenia, and Y. spanisbripes share the character of bodies covered by scales, Y. chuanheensis and Y. jiuchiensis are scaleless between the pectoral-fin and pelvic-fin bases. Yunnanilus polylepis sp. nov. can be further distinguished from Y. chuanheensis by six branched pelvic fin rays (vs. seven) and from Y. jiuchiensis by 10 inner gill rakers on the first gill arch (vs. eight) and an eye diameter smaller than the interorbital width (vs. larger). Yunnanilus polylepis sp. nov. can be distinguished from Y. longibulla, Y. macrogaster, Y. macrolepis, Y. parvus, Y. pleurotaenia, and Y. spanisbripes by processus dentiformis absent (vs. present). It can be further distinguished from Y. longibulla by eye diameter smaller than interorbital width (vs. larger), six branched pelvic fin rays (vs. seven or eight), caudal peduncle depth 12%–14% of SL (vs. 8%–10%), from Y. macrolepis and Y. spanisbripes by outer gill raker absent on first gill arch (vs. present), predorsal length 51%–55% of SL (vs. 56%–58% in Y. macrolepis), preanal length 73%–78% of SL (vs. 80%–82% in Y. macrolepis, 79%–82% in Y. spanisbripes), from Y. macrogaster by 10–11 branched pectoral fin rays (vs. 12 or 13), six branched pelvic fin rays (vs. seven), 10 inner gill rakers on first gill arch (vs. 13), body height 16%–20% of SL (vs. 22%–23%), eye diameter 17%–27% of lateral head length (vs. 12%), and from Y. parvus by nine branched dorsal fin rays (vs. eight), six branched pelvic fin rays (vs. seven), body height 15%–20% of SL (vs. 20%–23%).

Based on phylogenetic analysis, Y. analis was clustered with Y. pleurotaenia. However, due to the ambiguous geographical origin of Y. analis in GenBank (MW729320), its validity is not discussed in this study. Although molecular evidence from He et al. (2024) supported that Y. yangi belongs to Yunnanilus, the wrong sequence of niger was used in this publication (Du et al. 2023). Additionally, the phylogenetic tree weakly supported Y. yangi as a sister group to Eonemachilus; hence, the phylogenetic relationship between Eonemachilus and Yunnanilus will be discussed in the future. Despite the widespread distribution of Y. pleurotaenia, the majority of Yunnanilus species are restricted to more localized environments and habitats, including small ponds, streams, and lakes. While our phylogenetic analysis sheds light on the complex relationships among Yunnanilus species, it also underscores the urgency of addressing the environmental threats that jeopardize their survival, especially given their generally restricted distribution. Overfishing, agricultural runoff and siltation, organic pollution, habitat degradation, and increasing droughts have profoundly affected these endemic species. Notably, Jin et al. (2018) highlighted that the frequency, intensity, and impact of regional droughts have increased in Yunnan in recent years, with a particularly severe drought occurring in the spring and early summer of 2019 due to an abnormally delayed rainy season (Ding and Gao 2020). However, the specific effects of such droughts on the Yunnanilus population remain uncertain. Future studies focusing on taxonomic classification, biodiversity surveillance, and conservation assessments are deemed essential.

The electronic version of this article in portable document format represents a published work according to the International Commission on Zoological Nomenclature (ICZN), and hence the new name contained in the electronic version is effectively published under the Code in the electronic edition alone (see Articles 8.5–8.6 of the Code). This published work and the nomenclatural acts it contains have been registered in ZooBank LSIDs (Life Science Identifiers) and can be resolved, and the associated information can be viewed through any standard web browser by appending the LSID to the prefix http://zoobank.org/.

The authors declare that they have no competing interests.

Z.-X. Q. and L.-N.D. measured the specimens, analyzed the data, conceived and designed the study, and prepared the manuscript. W.-H. S. analyzed the molecular data and constructed the phylogenetic tree. Z.-X. W. provided funding for the field survey. All authors read and approved the final version of the manuscript.

This study was funded by the Guangxi Natural Science Foundation Project (2022GXNSFAA035563) and the Key Laboratory of Ecology of Rare and Endangered Species and Environmental Protection (Guangxi Normal University), Ministry of Education, China (ERESEP2022Z05). We are grateful to C. S. Yang for collecting specimens. We thank H. J. Chen for providing the living photographs of this species.