Recent ichthyofauna surveys in Phia Oac-Phia Den National Park, Vietnam, yielded 16 specimens of loach representing the genus Vanmanenia. These specimens were uniform in morphology and distinct from known species, leading to the designation of a new species, Vanmanenia duci sp. nov. This species is distinguished from congeners by the following combination of characters: pectoral fin: I, 15; pelvic fin: I, 8; lateral line scales 77–83; the distance from the anus to the posterior insertion of the pelvic fin being greater than from the anus to the anal fin origin; a lateral black stripe from the gill opening to the caudal fin base; a black spot at the caudal fin origin equal to the eye diameter; and a lower lip with three large papillae, with the middle one being larger. The new species differs from Vanmanenia caldwelli (Nichols, 1925) by its mouth soft-tissue structures and lower morphometric values and from Vanmanenia ventrosquamata (Mai, 1978) and Vanmanenia caobangensis Nguyen, 2005 by having more lateral line scales and lower body depth. Additionally, Vanmanenia duci sp. nov. has a larger eye and wider interorbital space compared to other species in Vietnam. This species is found in the Red River basin in Vietnam and the Bang Giang River flowing into China, indicating high potential for freshwater fish diversity in these river systems.

Bang Giang River, Gam River, new species, northern Vietnam, taxonomy, Vanmanenia

The genus Vanmanenia Hora, 1932, commonly known as hillstream loaches represents the family Gastromyzontidae, currently accommodates 24 species (Fricke et al. 2023). Some of its species were formerly assigned to Homalosoma Boulenger, 1901 (see Silas 1953). A total of 22 species can be found in southern China and Vietnam, i.e., Vanmanenia caldwelli (Nichols, 1925); Vanmanenia caobangensis Nguyen, 2005; Vanmanenia gymnetrus Chen, 1980; Vanmanenia hainanensis Chen et Zheng, 1980; Vanmanenia homalocephala Zhang et Zhao, 2000; Vanmanenia lineata (Fang, 1935); Vanmanenia maculata Yi, Zhang & Shen, 2014; Vanmanenia microcephala Li, Zhou et Che, 2019; Vanmanenia microlepis Nguyen, 2005; Vanmanenia monofasciodorsala Nguyen, 2005; Vanmanenia multiloba (Mai, 1978); Vanmanenia nahangensis Nguyen, 2005; Vanmanenia pingchowensis (Fang, 1935); Vanmanenia polylepis Pan, Liu et Zhang, 1983; Vanmanenia pseudostriata Zhu, Zhao, Liu et Niu, 2019; Vanmanenia serrilineata Kottelat, 2000; Vanmanenia stenosoma (Boulenger, 1901); Vanmanenia striata Chen, 1980; Vanmanenia tetraloba (Mai, 1978); Vanmanenia trifasciodorsala Nguyen, 2005; Vanmanenia ventrosquamata (Mai, 1978); and Vanmanenia xinyiensis Zheng et Chen, 1980 (see Li et al. 2019; Deng and Zhang 2020, 2021; Cai et al. 2021), and eight species in Vietnam (Nguyen 2005). Species in this genus prefer living in the fast-flowing waters of mountain brooks of China, Laos, and Vietnam (Yue et al. 2000; Yi et al. 2014). Thus, they could be diverse in the upper reaches of large rivers in northern Vietnam, such as the Red River and the Bang Giang River. In fact, of eight species recorded in northern Vietnam, seven are distributed in the Red River, i.e., V. microlepis , V. monofasciodorsala; V. multiloba, V. nahangensis, V. tetraloba, V. trifasciodorsala, and V. ventrosquamata (see Nguyen et al. 2019) and two species from the Bang Giang River in Cao Bang Province, i.e., V. ventrosquamata and V. caobangensis (see Nguyen 2005; Deng and Zhang 2020) (Fig. 1).

Figure 1. 

Distribution of species of the genus Vanmanenia in northern Vietnam.

During the first surveys of the ichthyofauna in in Phia Oac-Phia Den National Park, Cao Bang Province, northern Vietnam (Fig. 2) in 2020 and 2021, 16 specimens of Vanmanenia were collected. Details of their external morphology indicated that all of them were one species, and they did not conform to any of the hitherto known species of the genus Vanmanenia. Therefore, we decided to describe these specimens as a new species, Vanmanenia duci sp. nov. and provide a differential diagnosis to distinguish it from all its congeners.

Figure 2. 

Sampling sites of Vanmanenia duci sp. nov. in Phia Oac-Phia Den National Park, Cao Bang Province, northern Vietnam.

Two fieldwork surveys were carried out in May 2020 and May 2021 in Phia Oac-Phia Den National Park, Nguyen Binh District, Cao Bang Province, northern Vietnam. In this area, there are two different river basin systems, including the Gam River, one of the largest tributaries of the Red River, and the Bang Giang River, known as the Zuo River in China, an upper tributary of the Yu River in southern China (Pearl River basin) (Figs 1, 2). Fish samples were collected by a hand net and by electro-fishing within 30 min per sampling site under the permission of local authorities. From these surveys, a total of 16 specimens of loach representing the genus Vanmanenia was collected at stations DO.02 in the Gam River, DO.05, and DO.07 in the Bang Giang River (Fig. 2). Fish were fixed in 10% formalin solution, and subsequently preserved in 70% ethanol in the Museum of Biology, Hanoi National University of Education. Measurements and counts followed by Yi et al. (2014) and were taken from the left side of each specimen. Measurements were made point-to-point, to the nearest 0.1 mm using calipers, and expressed as a percentage.

Comparative material. Vanmanenia caldwelli: SOU 201807801, 5 specimens, 30.15–62.13 mm SL; China: Fujian Province: Fuqing City; Min River; 7 July 2018.

Species group with black mid-lateral stripe. Vanmanenia duci sp. nov. differs from all other species of Vanmanenia except V. caldwelli, V. lineata, and V. homalocephala by having a broad black midlateral stripe on the body (vs. having bars or irregular blotches) (Figs 3, 4, 7 in the presently reported study; fig. 278 in Yue et al. 2000; fig. 1 in Zhang and Zhao 2000). Vanmanenia homalocephala and V. lineata are distributed in Xi-Jiang of the Pearl River basin (Yue et al. 2000; Zhang and Zhao 2000; Deng and Zhang 2020). The new species could be distinguished from V. lineata by maxillary barbel and lower lip in the mouth (fig. 1 in Li et al. 2019; Fig. 5A in the presently reported study). Vanmanenia homalocephala and Vanmanenia duci sp. nov. could be distinguished by scales in lateral line (95–100 vs. 77–83) and color pattern on the back (5–6 vs. 19 dark saddle-backed stripes) (fig. 1 in Zhang and Zhao 2000; Fig. 3 in the presently reported study).

Figure 7. 

Vanmanenia caldwelli (62.1 mm SL) collected from the Min River, in Fuqing City, Fujian Province, China (Photos by Fan Li).

The last species having a black midlateral stripe on the body is V. caldwelli, which is distributed in Min-Jiang River (Deng and Zhang 2021), far from the study site. Both V. caldwelli and Vanmanenia duci sp. nov. share the same gross morphology (Table 2). However, values of the majority of the measurements of Vanmanenia duci sp. nov. are lower than the range of measurements of V. caldwelli, such as body depth (12.2%–18.7%), caudal-peduncle depth (7.9%–9.1%), or head length (15.4%–16.7%), although snout length and eye diameter of Vanmanenia duci sp. nov. are larger than those of V. caldwelli (59.2%–72.5%, 21.0%–30.4%; respectively) (Table 2). In addition, the distance from the anus to posterior end of pelvic fin is farther than the distance from the anus to anterior insertion of the anal fin (vs. closer). Both species have a longitudinal black stripe on the body (Figs 3, 7), but the starting position of this stripe in the two species is different. It starts from the tip of the snout in V. caldwelli and just behind the head in Vanmanenia duci sp. nov. The mouth structure is somewhat similar between the two species since they have a lower lip with three triangular lobes, the middle lobe larger than two lateral lobes, two pairs of maxillary barbel at the corner of the mouth, and the outer pair is larger than the lateral lobes (Fig. 5A, 5B). Nevertheless, the upper lip of Vanmanenia duci sp. nov. is thin, with four conspicuous lobulated papillae, rostral barbels alternate with lobulated papillae and rostral folds clear (vs. a thick upper lip, lobulated papillae are absent and rostral folds are unclear in V. caldwelli). The lower jaw of V. duci sp. nov. is larger and deeper (vs. small and shallow) (Figs 5A, 5B). Besides, both species have a slightly black spot in the middle caudal fin base, but Vanmanenia duci sp. nov. has a black spot equal to the eye diameter (vs. smaller than the eye diameter). Moreover, the number of black bands across rays of dorsal and caudal fins of species Vanmanenia duci sp. nov. are fewer than those in V. caldwelli (1, 2 vs. 2, 3, respectively). The caudal fin shape is also clearly different between the two species (slightly truncate in Vanmanenia duci sp. nov. vs. forked in V. caldwelli) (Figs 3, 7). There is a larger black dot at the base of the pelvic and pectoral fins and a fleshy larger black protrusion of pelvic fin base in the new species than those in V. caldwelli. The new species has a black dotted stripe along from the posterior end of the pectoral fin to the posterior insertion of the anal fin (vs. absent in V. caldwelli) (Figs 3, 7).

Species group without black mid-lateral stripe. The new species was collected in the Red River and the Bang Giang River (a tributary of the Pearl River in China) (Fig. 1). Thus, the presently reported study attempted to compare the morphology of the new species with known species of Vanmanenia in this group from the Red River and the Pearl River basins.

In the Red River, two species V. tetraloba, V. striata are present in this group from China (Li et al. 2019). These two species are different from the new species by body color patterns (flank with 11–21 vermiculations presence vs. absence) and mouth soft-tissue structures (figs. 7, 8 in Li et al. 2019; fig. 3 in Yi et al. 2014; Figs 3, 5A, 5B, 8A, 8B, 8C in the presently reported study). As we can see from Fig. 1, this genus is diverse in the Red River basin located in Vietnam. Differences between Vanmanenia duci sp. nov. and the six species of Vanmanenia occurring in the Red River basin from Vietnam are listed in Tables 3, 4. The new species could be distinguished from its congeners in the Red River basin by the number of scales in the lateral line (Table 3). For example, the new species has fewer lateral-line scales (77–83) than V. tetraloba (104–112), V. trifasciodorsala (169), V. monofasciodorsala (164), and V. microlepis (124–135). Furthermore, Vanmanenia duci sp. nov. has a shorter head than V. nahangensis (15.4%–16.7% vs. 20.70%) (Table 3), which is distributed in the Gam River, a different tributary of the Red River opposite to the Black River, where other four species of Vanmanenia present (Fig. 1). The records of this new species and others, such as Pareuchiloglanis sp. (Tran et al. 2021), Parazacco sp. (Duong et al. 2022), and Chimarrichthys nami (see Tran et al. 2023) further indicate that the Red River basin is a home of many freshwater fish species (Nguyen et al. 2019). In the Pearl River, in addition to V. lineata and V. homalocephala as mentioned above, there are four species of this genus, i.e., V. gymnetrus, V. intermidia, V. pingchowensis, and V. polylepis in China. The new species differs from V. gymnetrus, V. intermidia, and V. pingchowensis in body color patterns (a broad black midlateral stripe on the body vs. absence) and mouth soft-tissue structures (fig. 1 in Li et al. 2019; figs. 2, 3, 7 in Deng and Zhang 2020; Figs 3, 5A, 5B in the presently reported study). Vanmanenia duci sp. nov. can be distinguished from V. polylepis by the patch type on the caudal-fin base (complete vs. dissociated) (Li et al. 2019; Fig. 3 in the presently reported study). This character is also available to indicate the new species differing from V. lineata, V. homalocephala, V. caldwelli, V. striata, and V. pingchowensis (see Li et al. 2019). There are two species of Vanmanenia in the Pearl River from Vietnam, i.e., V. caobangensis and V. ventrosquamata (Fig. 1). Vanmanenia duci sp. nov. has a slightly similar number of fin rays as V. ventrosquamata and V. caobangensis (Table 3), but the new species has a shorter head than V. caobangensis (7.54%–9.81% vs. 20.04%–21.23%) and shorter caudal-peduncle than V. ventrosquamata (7.54%–9.81% vs. 12.56%). In addition, Vanmanenia duci sp. nov. is further distinct from the species from the Red River and Pearl River basins in Vietnam in having a bigger eye, and a wider interorbital (Table 3).

Figure 8. 

Mouth soft-tissue structures of three species of Vanmanenia distributed in the same river basin, the Red River in Vietnam and China: (A) Vanmanenia duci sp. nov., HNUE-F00304, 47.60 mm SL; (B) Vanmanenia striata, IHB 646482, 53.20 mm SL (Yi et al. 2014); (C) Vanmanenia tetraloba, SWFC 0512252, 75.30 mm SL (Li et al. 2019. Abbreviations: lj = lower jaw, mb = maxillary barbel, rb = rostral barbel, rf = rostral fold, uj = upper jaw, ul = upper lip, ll = lower lip, lb = lobulated papillae.

Remarkably, Vanmanenia duci sp. nov. differs from other species of the genus in the Red River and Pearl River systems in Vietnam by presenting a longitudinal black stripe from the back of the head to the caudal fin origin along the lateral line on the side of the body and mouth soft-tissue structures (Figs 3, 5A; Table 4).

This research was funded by The NEF Bio-ecological Nature Conservation Project in the Mountainous Region of North Vietnam (Nagao Natural Environment Foundation, Japan/Central Institute for Natural Resources and Environmental Studies). Thanks to V.S. Ngo, T.T. Tran, H.V. Pham, N.T. Nguyen, A.N.T. Do, who assisted in collecting specimens. We thank anonymous reviewers for their comments that helped improve the manuscript.