Hemymizon yushanensis, Chen & Harefa & Chang & Han, 2022

Chen, I-Shiung, Harefa, Tonisman, Chang, Yung-Ching & Han, Chiao-Chuan, 2022, Hemimyzon yushanensis, a new species of balitorid fish (Teleostei: Baltiordae) from southern Taiwan, Zootaxa 5189 (1), pp. 6-12 : 7-11

Hemymizon yushanensis new species

( Figure 1 )

Holotype.- NTOUP-2021-12-325, 55.3 mm SL, Nar-Mar-Shar County, Nan-Tsi-Shien River, Kaoping River basin, coll. C.C. Han, July, 20, 2021, Kaohsiung City, Taiwan, ROC.

Paratypes.- NTOUP-2021-12-326, 8 specimens, 51.9–66.6 mm SL, Nar-Mar-Shar County, Nan-Tsi-Shien River, Kaoping River basin, Coll. C.C. Han, July, 20, 2021, Kaohsiung City, Taiwan, ROC .

Non-types.- NTOUP-2007-12-175, 5 specimens, 37.6–55.0 mm SL, Jo-Kou River, Kaoping River basin, Coll. By I-S. Chen, Oct. 15, 1995.

Diagnosis

The new species can be well distinguished from other congeneric species by following combination of features: (1) dorsal fin rays 3 + 8; pectoral fin rays 11–13 + 9–11 (total 22–23; modally 22); (2) lateral-line scales 69–72 (modally 70); predorsal scales 25–30 (26–27); (3) pelvic fin moderate large, extending to rear vertical of dorsal fin; (4) position of anus with larger distance of pelvic rear tip to anus about 1.5–2.0 times of that of anus to anal fin origin; and (5) specific coloration: predrorsal region and head with rounded creamy yellow spots, pectoral and pelvic fins with several small whitish spots on greenish brown background.

Description

The morphometrics of this new species as percentages of standard length are listed in Table 1 and meristic features are listed in Table 2. Head and body strongly depressed with flat ventral side anteriorly. Posterior trunk from anus to caudal peduncle rather compressed. See Table 1 for morphometric characters. Head with a few tiny tubercles. Upper lip with 16-18 small papillae; no distinct papillae on lower lip except a pair of somewhat crescent projections on inner side. Four rostral barbels and two barbels at both corners of mouth which anterior one much larger than the very tiny posterior one. The length of anterior barbels less than the eye diameter. Interorbital region rather wide. Gill-opening small and very restricted, merely extending above anterior origin of pectoral fin. The location of anus is closer to anal fin origin, with large distance of rear tip of pelvic fin to anus about 1.2-1.7 times to that of anus to anal fin origin.

Dorsal fin 3+8; anal fin 2+5; pectoral fin 11–13 + 9–11 (total 22–23; modally 22); pelvic fin 4–6 + 9–10 (totally 13–15 modally 14). Origin of dorsal fin behind origin of pelvic fin origin. Pectoral fin rather large, its rear margin extending beyond origin of pelvic fin. Pelvic fin well separate, the gap between the attachment of their innermost rays about 1.5-2.0 times of eye diameter; its rear margin extending to or beyond the rear tip of dorsal fin when depressed. Caudal fin forked, its lower lobe longer than upper one.

Dorsal part of body with very small cycloid scales, larger specimens with reduced, smaller cycloids which not reaching the nape. Larger specimens with reduced, smaller size of predorsal scales. Ventral region between the paired fins naked. Body scales slightly larger posteriorly. Lateral-line scales 69–72 and predorsal scales 25–30.

Coloration in fresh

Dorsum of body olive brown. Predrorsal region and head olive brown to deep brown with rounded creamy yellow spots, pectoral and pelvic fins with several small whitish spots on greenish brown background. The rear part of dorsal region behind dorsal fin with some irregularly creamy yellow marks. Lateral body uniformly olive brown to deep brown. Ventral side unique pale white. Dorsal fin pale white with deep brown rays with 2 major horizontal rows of creamy white spots. Anal fin pale white with deep brown rays. Caudal fin with broad black outer margin with 3–4 oblique, zigzag creamy white streaks.

Distribution

The new species is only found from the several localities of hill streams of the Kaoping River basin, both Kaohsiung City and Pingtung County and also the southern region of the Yushan National Park.

Etymology

The specific name, yushanensis is referred to the main drainages of Kaoping River originating and southward from the highest mountain of Taiwan, the Yushan mountain Ridge.

H: Holotype; P: Paratype.

Discussion

In the taxonomy of Hemimyzon , four nonimal species were documented in mainland China ( Yue 2000) while recorded two endemic species (Tzeng & Chen 1982; Shen 1993) before 2000. After then, Chen and Fang (2009) described Hemimyzon sheni from eastern Taiwan added the third endemic species to Taiwan.

Before the current species description of this new balitorid fish, Chen & Chang (2005) firstly mentioned for the potential, undescribed species ( Hemimyzon sp. ) from Kaoping River basins. Therefore, soon after Wang et al. (2007) published the molecular phylogenetics of this balitorid genus in Taiwan based on mtDNA D-loop sequences. Wang et al. (2007) clearly mentioned the results: the deep mtDNA genetic divergence implies that cryptic species might have arisen from southern population of H. formosanus , which is unique in differing from others in Taiwan; a recent study ( Chen & Chang 2005) described several morphological differences between southern population of Hemimyzon formosanus and other populations of H. fromosanus , which supports the southern population being a cryptic species. In summary, both independent studies strongly suggest that the so-called “southern population” from the Kaoping river basin should be classified as a distinct species.

In the zoo-geographical pattern of primary freshwater fishes in Taiwan, the distribution of the new species, H. yushanensis , shares the same geographical region with the Opsariichthys kaopingensis, Gobiobotia intermedia, Sinogastromyzon nantaiensis , Rhinogobius nantaiensis and also Rhinogobius sp. It reflects the same congruent speciation event for those fish genera which happened in “the same historical event of great isolation” of the Kaoping River basin, southern Taiwan ( Chen & Chang 2005; Chen unpublished data).

Since their high endemicity in Taiwanese waters, the new species H. yushanensis established, this species at least can be found from hill tributaries of the Kaoping River basin in the both regions of Kaohsiung City and Pingtung County. Therefore, the true range of H. formosanus would be restricted to further northern regions as all river basins from the Ilan County, Taipei City, Taipei City, Taoyuan City, Shinchu County, then southward to Tainan City which mainly in the western slope of Central Mountain Ridge. H. taitungensis can be seen from 3 main river basins from Hualian to Taitung County. H. sheni can only be seen in Tarchu river basin of Taitung County. Among them, all of them share allopatric distribution pattern without range overlapping.

Among the three endemic species of Taiwan, about the differentiation of dorsal fin rays, there are apparently two groups of Hemimyzon in Taiwan. One group is dorsal fin rays 3+7 which seen in wide distributed species, H. formosanus ; another group is dorsal fin rays 3+8 which can be seen in the following three species as H. taitungensis , H. sheni as well as H. yushanensis . The 3+8 group only can be seen in eastern Taiwan as both H. taitungensis and H. sheni . H. yushanensis can be only found from the Kaoping River basin originating from southern slope of the Yushan mountain Ridge in southern Taiwan.

H. yushanensis shares the same dorsal fin ray formula, 3+8 with both H. taitungensis and H. sheni . However, H. yushanensis can be well distinguished from H. taitungensis by the pectoral fin rays 22–23 vs. 25–26; pelvic fin rays 13–15 vs. 17. It also can be well distinguished from H. sheni by the lower counts of pectoral fin rays 22–23 vs. 24; lateral-line scales 69–72 vs. 78–80; rear tip of pelvic fin extending to or beyond dorsal fin when depressed vs. rear tip of pelvic fin not extending to dorsal fin when depressed. The limited distribution of current species is needed for further concern of conservation issue.

Figures

FIGURE 1. Hemimyzon yushanensis, holotype, NTOUP-2021-12-325, 55.3 mm SL, a, dorsal view; b, lateral view; c. ventral view; Nan-Tsi-Shien River, Kaoping River basin, Kaohsiung City, Taiwan, ROC.