Oreonectes damingshanensis Yu, Luo, Lan, Xiao & Zhou, 2023

Yu, Jing, Luo, Tao, Lan, Chang-Ting, Zhou, Jia-Jun, Deng, Huai-Qing, Xiao, Ning & Zhou, Jiang, 2023, Oreonectes damingshanensis (Cypriniformes, Nemacheilidae), a new species of stream fish from Guangxi, Southwest China, ZooKeys 1180, pp. 81-104 : 81

Oreonectes damingshanensis Yu, Luo, Lan, Xiao & Zhou sp. nov.

Figs 4 , 5 , 6

Chresonymy.

Oreonectes platycephalus ( Günther, 1868): Wang 2022 (Guangxi, China); Luo et al. 2023 (Damingshan Mountains, Shanglin County, Guangxi, China).

Material.

Holotype. GZNU20230216001, 98.9 mm total length (TL), 81.8 mm standard length (SL), collected by Jing Yu on February 16, 2023, in Waminggu Scenic Area , Leping Village , Guling Town , Mashan County, Guangxi Zhuang Autonomous Region, China (23.60818443°N, 108.29426408°E; ca. 234 m a.s.l.) . Paratypes. Twenty-four specimens from the same locality as the holotype: GZNU20230216002-216025, 46.2-70.7 mm SL, collected by Jing Yu and Tao Luo on February 16, 2023 . Five specimens from Damingshan Mountains , Shanglin County, Guangxi: GZNU2020011505-011509, 59.2-76.7 mm SL, collected by Yali Wang and Tao Luo on February 16, 2021 .

Etymology.

The species epithet damingshanensis refers to the type locality, located within the Damingshan Mountains, Guangxi, China. The suggested English name is the Damingshan Mountains loach, and the Chinese name is Dà Míng Shān Lıˇng Qiū (大明山岭鳅).

Diagnosis.

Oreonectes damingshanensis sp. nov. is assigned to the genus Oreonectes based on molecular phylogenetic analyses and the following characteristics, which are diagnostic for this genus: (1) anterior and posterior nostrils narrowly separated; (2) lips smooth, with furrows; (3) barbel-like elongation of anterior nostrils longer than depth of nostril tube; and (4) caudal fin rounded, dorsal fin with 6 or 7 branched rays ( Du et al. 2023).

Oreonectes damingshanensis sp. nov. can be distinguished from all other congeners by the following combination of characters: (1) body pigmentation present; (2) eyes normal, diameter 6.5-17.1% of head length; (3) caudal fin rounded, with irregular black markings; (4) body completely covered with fine scales except for the head; (5) lateral line incomplete, with 14 or 15 pores, last lateral line pore reaching above the tip of pectoral fin; (6) dorsal-fin rays, iii-7; (7) pectoral-fin rays, i-9; (8) anal-fin rays, iii-5; (9) pelvic-fin rays, i-7; (10) 14 branched caudal-fin rays; (11) tip of ventral fin extended backward, not reaching the anus; (12) dorsal fin origin posterior to the pelvic-fin origin; (13) inrostral barbel extending backward and not reaching the anterior margin of the eye; (14) tip of maxillary barbel not reaching the posterior margin of the gill cover; and (15) vertebrae 4 + 34.

Description.

Body elongated and cylindrical, with the insignificant depth decreasing from dorsal-fin origin to caudal-fin base. Head short, length 13.3 mm, slightly depressed and flattened, width greater than depth (head width/head depth = 1.3). Snout round, oblique and flat, length 38.0-45.3% of head length (HL). Mouth inferior, curved, upper and lower lips smooth, lower lip with a V-shaped median notch. Three pairs of barbels are long: inrostral barbel length 25.9-38.3% of HL, extending backward and not reaching the anterior margin of eye; outrostral barbel length 42.4-62.4% of HL, extending backward beyond the posterior margin of the eye. Maxillary barbel length 36.0-56.6% of HL, tip of maxillary barbel not reaching to posterior margin of gill cover. Anterior and posterior nostrils narrowly separated, length 33.5-84.2% of eye diameter. Anterior nostril tube short, with an elongated short barbel-like tip. Eyes present, normal, diameter of 6.5-17.1% HL. Gill opening small; gill rakers not developed, nine inner gill rakers on the first gill arch (n =1) (Fig. 4D ).

Dorsal-fin rays iii-7, pectoral-fin rays i-9, pelvic-fin rays i-7, anal-fin rays iii-5, 14 branched caudal fin rays. Dorsal fin short, length 15.8-22.6% of SL, distally margin round, origin posterior to pelvic-fin insertion, situated slightly posterior to two-thirds the distance between snout tip and caudal-fin base. Pectoral fin short, length 15.2-19.5% of SL, tip of pectoral fin extending backward to ~56.7% of the distance between the origin of pectoral and pre-pelvic fins. Pelvic fin length 13.1-17.2% of SL, tips of pelvic fin not reaching anus, distance between tips of pelvic fin and anus 2.0 times the eye diameter. Anal fin long, length 15.3-179.7% of SL, tips of anal fin not reaching caudal-fin base, distance between tips of anal fin and anus 0.64 times the eye diameter. Caudal fin rounded, caudal peduncle length 9.3 mm, without adipose crests along either dorsal or ventral sides. Vertebrae 38 comprising of 4 Weberian + 22 abdominal + 11 caudal + 1 compound centrum (Fig. 5 ).

Except for the head, body completely covered by scales. Lateral line incomplete, exceeding tip of pectoral fin but not reaching base of caudal fin, with 14 or 15 pores, last lateral line pore reaching above the tip of pectoral fin. Cephalic lateral-line system, with eight supraorbital, 5 + 8 infraorbital canal pores, three supratemporal canal pores, with eight preoperculo-mandibular canal pores. Two chambers of air-bladder, posterior chamber developed, filling the body cavity and connected with anterior chamber by a long, slender tube. Lateral wall of the bony capsule of the swim bladder is membranous and closed posteriorly (Fig. 5 ).

Coloration.

In life, body pale yellow-brown overall, dark brown between anterior margin of eyes to outrostral barbel, brown lateral stripe on flank of the body, irregular black spots present on dorsal and lateral surfaces and caudal fin, black at base of caudal fin, pale brown on each fin (Fig. 6 ). In 10% formalin, the body color was dark brown (Fig. 4 ).

Comparisons.

Comparative data of Oreonectes damingshanensis sp. nov. with the five known species within the genus Oreonectes are given in Table 1 .

Oreonectes damingshanensis sp. nov. can be distinguished from O. luochengensis by nine branched pectoral-fin rays (vs 11 or 12), lateral line pores 14 or 15 (vs 6-13), caudal fin rounded, with irregular black markings (vs truncated, without irregular black markings), body covered with scales except for the head (vs degraded, body scales hidden under the skin), and vertebrae 4 + 34 (vs 4 + 32 /35).

Oreonectes damingshanensis sp. nov. can be distinguished from O. guilinensis by dorsal-fin rays (iii, 7 vs ii, 6), seven branched pelvic-fin rays (vs 6), lateral line pores 14 or 15 (vs 4-6), black at base of caudal fin (vs absence), maxillary barbel extending backward, not reaching to the posterior margin of the gill cover (vs reaching to posterior margin of the eye), and tip of pelvic fin not reaching to anus (vs reaching to anus).

Oreonectes damingshanensis sp. nov. can be distinguished from O. guananensis by nine branched pectoral-fin rays (vs 10 or 11), dorsal fin origin posterior to pelvic-fin origin (vs opposite to pelvic-fin origin), maxillary barbel extending backward and not reaching to posterior margin of gill cover (vs reaching to the gill cover), lateral line pores 14 or 15, last lateral line pore reaching above the tip of pectoral fin (vs 7-13, last lateral line pore not reaching above the tip of pectoral fin), caudal fin with irregular black markings (vs without irregular black markings), vertebrae 4 + 34 (vs 4 + 32), relatively small eye diameter (1.6 ± 0.3 mm vs 5.8 ± 1.9 mm, p -value = 0.00, Table 4 ) and some significant morphological differences (p -values <0.05), including head depth (4.7 ± 0.8 mm vs 3.1 ± 1.0 mm), head width (9.7 ± 1.3 mm vs 7.0 ± 1.8 mm), mouth width (7.2 ± 1.0 mm vs 4.7 ± 1.5 mm), interorbital distance (5.6 ± 0.9 mm vs 1.7 ± 0.4 mm), pectoral-fin base length (2.4 ± 0.4 mm vs 1.8 ± 0.5 mm), pelvic-fin base length (2.3 ± 0.4 mm vs 1.2 ± 0.5 mm), and anal-fin base length (5.2 ± 0.6 mm vs 4.2 ± 0.8 mm).

Oreonectes damingshanensis sp. nov. differs from O. platycephalus by having seven branched dorsal-fin rays (vs 8 or 9), nine branched pectoral-fin rays (vs 11), seven branched pelvic-fin rays (vs 8), anal-fin rays (iii, 5 vs ii, 6 or 7), nine inner gill rakers on the first gill arch (vs 14 or 15), and maxillary barbel extending backward, not reaching to the posterior margin of the gill cover (vs reaching to the posterior margin of the eye).

Oreonectes damingshanensis sp. nov. can be distinguished from O. polystigmus by having seven branched pelvic-fin rays (vs 6), nine branched pectoral-fin rays (vs 10), seven branched pelvic-fin rays (vs 6), anal-fin rays (iii, 5 vs ii, 5), lateral line pores 14 or 15 (vs 6-8), nine inner gill rakers on first gill arch (vs 13 or 14), tip of pelvic fin not reaching to anus (vs reaching to anus), maxillary barbel extending backward, not reaching the posterior margin of the gill cover (vs reaching the pectoral-fin origin), and vertebrae 4 + 34 (vs 4 + 32). In addition to differences in each fin, the new species also differed significantly from O. polystigmus in a number of measurable characters. These included larger head length (13.3 ± 1.7 mm vs 11.6 ± 1.0 mm), head width (9.7 ± 1.3 mm vs 7.7 ± 0.3 mm), mouth width (4.7 ± 0.8 mm vs 3.1 ± 0.4 mm), eye diameter (1.6 ± 0.3 mm vs 0.9 ± 0.2 mm), dorsal-fin length (11.4 ± 1.4 mm vs 9.5 ± 0.3 mm), pelvic-fin length (9.6 ± 1.3 mm vs 7.5 ± 0.4 mm), and anal-fin length (10.4 ± 1.2 mm vs 8.1 ± 0.4 mm) (p -value <0.05; Table 4 ).

Distribution, habitat, and populations.

Based on current field surveys, the new species Oreonectes damingshanensis sp. nov. has only been found in streams in the Damingshan Mountains of Mashan and Shanglin counties in the Guangxi Zhuang Autonomous Region of China belonging to the Hongshuihe River basin of the Pearl River system. The new species is easy to collect in the streams of the Damingshan Mountains area where it has a large population.

Figures

Figure 4. Morphological characteristics of the holotype GZNU 20230216001 of Oreonectes damingshanensis sp. nov. in preservative (10 % formalin) A lateral view B dorsal view C ventral view D gill raker E enlarged anterior and posterior nostrils.

Figure 5. The three-dimensional reconstructed model of the skeleton of Oreonectes damingshanensis sp. nov. (paratype GZNU 20230216021, standard length 57.0 mm) A dorsal view B ventral view, and C latera view. Caudal fin slightly broken.

Figure 6. Live paratype of Oreonectes damingshanensis sp. nov.