In a recent survey of populations of the Korean torrent catfish Liobagrus, a distinctive species was discovered from the Geum River and its tributaries flowing into the western coast of Korea, and here described as a new species, L. geumgangensis sp. nov. It is distinguishable from other congeners by a combination of the following characters: I, 8 pectoral fin-rays; 52–56 caudal-fin rays; a relatively short occiput to dorsal-fin origin distance (6.9–9.8% SL); a short pelvic-fin insertion to anal-fin origin distance (11.9–17.3% SL); a long dorsal-fin base (10.6–13.5% SL); 8–9 gill rakers; 5–8 serrations on the pectoral fin; the body and fins are dark yellow, the margins of the dorsal, anal, and caudal fins are dark brown, but the outermost rim is faintly yellow. Analysis of the cytb gene also confirmed that L. geumgangensis is a monophyletic lineage distinct from other congeners.

Catfishes, cytb, DNA, geographical speciation, key, morphometrics, taxonomy

The family Amblycipitidae, which includes four genera (Liobagrus Hilgendorf, 1878; Amblyceps Blyth, 1858; Xiurenbagrus Chen & Lundberg, 1995; Nahangbagrus Nguyen & Vo in Nguyen 2005), is restricted to southern and eastern Asia, including Pakistan (Amblyceps), and across northern India (Amblyceps) through Myanmar, Laos, Cambodia, Thailand to Malaysia (all Amblyceps), Vietnam (Nahangbagrus), China (Amblyceps, Liobagrus, Xiurenbagrus), Korea (Liobagrus), and southern Japan (Liobagrus) (Chen and Lundberg 1995; Ng and Kottelat 2000; Kim and Park 2002; Wright and Ng 2008; Park and Kim 2010; Kim et al. 2015; Chae et al. 2019).

Genus Liobagrus can be distinguished from the genus Amblyceps by its pale fin margins, adipose fin confluence with the caudal fins, rounded or truncated caudal fin (Wright and Ng 2008), and main distribution in eastern Asia. Including the most recently described species, L. brevispina, 14 species have been reported from the Yangtze River (Changjiang) in mainland China, five species from Korea, and one species from Japan, for a total of 20 species. Liobagrus from the Korean Peninsula have been described with the following characteristics: L. andersoni Regan, 1908c, is distinguished by upper and lower jaws of equal length; L. mediadiposalis Mori, 1936, by a shorter lower than upper jaw; L. obesus Son, Kim & Choo, 1987 by fewer serrations on the pectoral fin; L. somjinensis Park & Kim, 2010, by the broad yellowish, vertical, crescent-shaped band in the middle of the caudal fin; and L. hyeongsanensis Kim, Kim & Park, 2015 by its small size, with a maximum standard length of 90 mm, and body and fins that are entirely yellowish brown without distinct markings.

The Korean Peninsula is largely divided into western and eastern halves by the Baekdudaegan Mountain Range. Recent studies on freshwater fish from Korea have focused on taxonomic reviews of fish separated by this range: Koreocobitis rotundicaudata (West), Wakiya and Mori 1929 vs. K. naktongensis (East), Kim et al. 2000; Coreoleuciscus splendidus (West), Mori 1935 vs. C. aeruginos (East), Song and Bang 2015; Cobitis nalbanti (West), Vasil’eva et al. 2016 vs. C. hankugensis (East), Kim et al. 2003. Following this logic, it is suspected that subpopulations of L. mediadiposalis, which are widely distributed across river drainages from the western (Geum River) to the southeastern (Nakdong River) portions of South Korea, may actually represent distinct species (Son 1987; Kim et al. 2006; Kim 2013). In this study, we investigate the identity of L. mediaposalis from the Geum River and confirm its distinctiveness from L. mediadiposalis s. str., describing it here as Liobagrus geumgangensis, a new species.

Compared with the original descriptions of Liobagrus (Hilgendorf 1878; Gűnther 1892; Regan 1904, 1908a, b, c; Oshima 1919; Nichols 1926; Wu 1930; Tchang 1935; Mori 1936; Son et al. 1987; Wright and Ng 2008; Park and Kim 2010; Kim et al. 2015) and based on coloration and meristic and morphometric data, we confirmed that L. geumgangensis sp. nov. is distinct from L. mediadiposalis. The number of pectoral fin rays is I, 8 in L. geumgangensis (vs. I, 7 in L. mediadiposalis) and the number of caudal fin rays is 52–56 (average 54.9) (vs. 57–61). The distance between the occiput and dorsal-fin origin is shorter at 6.9–9.8% SL than L. mediadiposalis (10.3–13.3% SL). The relative lengths of the upper and lower jaws are a key characteristic used in identifying Liobagrus species, with three possible states identified: lower jaw longer than upper (L. marginatoides, L. marginatus, L. kingi, and L. chengduensis), jaws of equal length (L. andersoni, L. obesus, L. nigricauda, L. anguillicauda, L. brevispina, L. aequilabris, and L. formosanus), and upper jaw longer than lower (all remaining congeners; Table 3). On the Korean Peninsula, L. andersoni and L. obesus have jaws of equal length, whereas L. geumgangensis, along with L. mediadiposalis, L. somjinensis and L. hyeongsanensis, have a lower jaw shorter than its upper jaw. Liobagrus mediaposalis, L. somjinensis and L. hyeongsanensis all have I, 7 pectoral-fin rays; just two species, L. andersoni and L. geumgangensis have I, 8 pectoral-fin rays. The pectoral fin rays are not used as a common diagnostic characteristic and are considered to be species-specific variables, but in contrast, some studies have suggested fixed results (Xie et al. 2022). Since this study did not measure a large number (N = 30) of L. andersoni specimens, it is possible that the number of pectoral fin rays may vary, but this study intends to use this as a comparative characteristic.

To summarize, within the Liobagrus distribution in Korea, it is noteworthy that L. geumgangensis is the only species with an upper jaw longer than the lower jaw and I, 8 pectoral fin rays. In addition, L. geumgangensis differs from L. somjinensis in several characters: absence vs. presence of a broad vertical yellowish crescent-shaped band on the caudal fin, with a deep black outer margin; 5–8 vs. 4–6 serrations on the pectoral fin; and 52–56 caudal fin rays vs. 57–61 (Fig. 4).

Liobagrus geumgangensis is allopatrically distributed in restricted river systems, the Geum River and a patch of the Mangyeong River, which flow toward the western coast of Korea. Unlike other Liobagrus species, L. somjinensis is restricted to rivers flowing to the west coast and Geogeum Island, the Somjin, Dongin and Tamjin rivers. Liobagrus hyeongsanensis has a much smaller distribution including the Hyeongsan River flowing into the east coast, whereas L. mediadiposalis is found only in the Nakdong River on the west coast (Fig. 5). Liobagrus andersoni is restricted to the Han River system alone. Meanwhile, L. obesus has a wide distribution including the western river systems of Geum, Yeongsan and Mangyeong, and their distribution overlaps with other congeners. Interestingly, based on morphological and genetic research, all six species of the Korean Liobagrus are endemic (Kim et al. 2006, 2015; Park and Kim 2010; Kim 2013).

Our results are consistent with a recent study by Kim et al. (2006) on the evolutionary relationships among L. mediadiposalis populations in Korea using cytochrome b sequences. Kim et al. (2006) considered Type I to be the Somjin River group, which included four populations (Dongin, Somjin, and Yeongsan rivers and Geogeum Island), and Type II as the Geum River group comprising a single population. Although they confirmed that the Geum River group was genetically distinct from L. mediadiposalis, the taxonomy of this population was not further investigated. Here, our analysis of seven different populations confirms that the Geum River group represents a distinct, unnamed species (Fig. 3).

Figure 3. 

Phylogenetic tree using maximum likelihood (ML) method based on mitochondrial cytochrome b gene sequences of Siluriformes species including L. geumgangensis. Bootstrap support values based on 1000 replicates are displayed on each node as >50. The blue color of the branches indicates L. geumgangensis.

Figure 4. 

Liobagrus mediadiposalis (A), CNUC 39153, 97.0 mm SL; male, Nakdong River, Sancheong-gun, South Korea and L. somjinensis (B), CNUC 39170, 99.4 mm SL, male, Somjin River, Namwon-si, South Korea.

The geographical isolation of the freshwater fish of South Korea is likely related to the geological origins of the Korean Peninsula. The Korean Peninsula was formed by active orogeny movements from the early Triassic to the Jurassic. The structure of the current complex topography is due to the tectonic shift concentrated in the Tertiary Period of the Cenozoic Era. As a result, Korea has an approximately 1400 km long mountainous region stretching from North Korea to South Korea. The peninsula, called the Baekdudaegan, contains at least 12 mountain ranges that have formed unique rivers, including the Han, Geum, Nakdong, Hyeongsan, and Mangyeong rivers (Chough et al. 2000; Sohn et al. 2001). Consequently, some Korean freshwater fish are distributed allopatrically, causing speciation.

According to Mori (1936) and Kim (1997), the freshwater fish fauna on the Korean Peninsula is divided into three biogeographical regions: northeast, west, and southern Korea subdistricts. Such biogeographical distributions based on large mountain ranges creating physical barriers and allopatric distributions lead to endemic species (Fig. 5). In particular, Korean cobitid fishes, including 10 endemic species, are the best example of a diverse regional distribution (Kim and Park 2002; Chae et al. 2019). Some mountain ranges between the west and south subdistricts serve as strong long-term barriers to recurrent gene flow. Such barriers led to the split of Coreoleuciscus splendidus populations into two genetically discrete subdistrict populations (Kim et al. 2012). Geographical speciation has also been observed among some species of the Cyprinidae family on the Korean Peninsula (Kim 1997; Kim and Park 2002; Park and Kim 2010). Isolation of fish populations in different river systems has led to high levels of endemism in Korean Liobagrus, including L. geumgangensis.

Figure 5. 

South Korea, showing distributions of Liobagrus geumgangensis (1–7), L. somjinensis, L. hyeongsanensis, and L. mediadiposalis. Dark green line: Baekdudaegan mountain range, showing three biogeographical ranges of ichthyofaunal endemism on the Korean Peninsula (modified from Kim 1997).

We thank Prof. H. T. Kim at Jeonju National University of Education, Jeonju, South Korea, and Mr. J. U. Kim at Jeonbuk National University, Jeonju, South Korea for collecting samples from several streams.