Pungitius sinensis ( Guichenot 1869 )

Matsumoto, Tatsuya, Matsuura, Keiichi & Hanzawa, Naoto, 2025, Redescription of the Chinese ninespine stickleback, Pungitius sinensis (Guichenot 1869) (Gasterosteiformes, Gasterosteidae), Zootaxa 5728 (1), pp. 144-162 : 146-159

Pungitius sinensis ( Guichenot 1869)

[English name: Chinese ninespine stickleback; standard Japanese name: Tomiyo]

Figs, 1–8; Tables 1–4

Gasterosteus sinensis Guichenot 1869: 204 , Pl. 12, fig. 4 ( type locality: China).

Gasterosteus wosnesenjenskyi Kessler 1876: 9 , ( type locality: western Kamchatka, Russia).

Gasterosteus japonicus Steindachner 1881: 264 , Pl. 3, fig. 2 ( type locality: Strelos Bay, near Vladivostok, Russia), junior homonym of Gasterosteus japonicus Houttuyn 1782 .

Pygosteus steindachneri Jordan & Snyder 1901: 747, (replacement name for Gasterosteus japonicus Steindachner 1881 ).

Pygosteus brevispinosus Otaki 1908: 87 , ( type locality: Sapporo , Hokkaido, Japan).

Type specimens. Syntypes of Gasterosteus sinensis Guichenot 1869 , MNHN 0000-5228, 7 specimens, 20.0 + – 25.7 mm SL, China .

Other type specimens. Syntypes of Gasterosteus wosnesenjenskyi Kessler 1876 , ZIN 2377 , 2 of 7 specimens, 23.8 and 28.7 mm SL, ZIN 2378 , 6 of 9 specimens, 50.4–77.3 mm SL, western Kamchatka, Russia .

Non-type specimens. 368 specimens ( 18.5–82.2 mm SL). China: CBM 13938 , 2 specimens, 43.6 and 38.4 mm SL, Fushun, Liaoning. Russian Far East : HUMZ 225936 , 1 of 8, 43.5 mm SL, Anadyr; HUMZ 239396 , 2 , 46.4 and 50.2 mm SL, Mikijia River, Kamchatka ; HUMZ 236398 , 3 , 46.4–50.2 mm SL, Bolshaya River, Kamchatka ; NSMTP 110558 , 41.1 mm SL, Cape Lion, Primorsky Krai. Korean Peninsula: YCM-P 12656, 2, 39.3 and 41.7 mm SL, Seon River, Gangwong-do; YCM-P 12658, 3, 36.5–44.8 mm SL, Jusu River, Gangwong-do. Sakhalin Island : HUMZ 140285 , 80.2 mm SL, HUMZ 140286 , 72.8 mm SL, HUMZ 140288 , 76.6 mm SL, HUMZ 140290 , 63.9 mm SL,; HUMZ 140321 , 53.8 mm SL, HUMZ 158608 , 49.3 mm SL, HUMZ158614 , 40.3 mm SL, HUMZ 158617 , 59.9 mm SL, HUMZ 158623 , 58.7 mm SL, HUMZ 158625 , 43.6 mm SL, HUMZ 158627 , 48.0 mm SL, HUMZ 158634 , 52.7 mm SL, HUMZ158637 , 54.2 mm SL, HUMZ 158641 , 45.5 mm SL, HUMZ 158642 , 63.6 mm SL, HUMZ 158645 , 63.8 mm SL, HUMZ 158649 , 82.2 mm SL, HUMZ 158657 , 50.8 mm SL, HUMZ 158663 , 58.5 mm SL, HUMZ 158680 , 58.3 mm SL, HUMZ 158674 , 60.5 mm SL, HUMZ 158675 , 65.6 mm SL, HUMZ 158678 , 59.3 mm SL, HUMZ 183505 , 47.2 mm SL, HUMZ 183506 , 37.0 mm SL, HUMZ 183507 , 64.5 mm SL, HUMZ 183592 , 46.9 mm SL, HUMZ 183594 , 56.6 mm SL, Piltun Bay ; HUMZ 183222 , 46.8 mm SL, HUMZ 183223 , 39.5 mm SL, HUMZ 183224 , 47.2 mm SL, HUMZ 183226 , 46.2 mm SL, HUMZ 183228 , 52.3 mm SL, Aynskaya River ; HUMZ 183320 , 42.3 mm SL, HUMZ 183322 , 48.5 mm SL, Lake Aynskaya ; HUMZ 236401 , 5 , 54.4–67.5 mm SL, Tym River ; HUMZ 236403 , 3 , 52.0– 56.2 mm SL, Lake Tunaicha. Kuril Islands : HUMZ 155050 , 44.5 mm SL, HUMZ 155053 , 43.1 mm SL, HUMZ 155054 , 40.1 mm SL, HUMZ 155055 , 39.1 mm SL, HUMZ 155056 , 37.7 mm SL, HUMZ 155059 , 38.8 mm SL, Urup Island ; NSMT-P 69952 , 3 , 31.1 – 45.0 mm SL, Fribetsu River, Etorofu Island. Japanese Archipelago, Hokkaido Island : HUMZ 64500 , 49.1 mm SL, HUMZ 64501 , 42.9 mm SL, HUMZ 64502 , 51.0 mm SL, HUMZ 64503 , 49.8 mm SL, HUMZ 64504 , 60.5 mm SL, HUMZ 64505 , 66.1 mm SL, HUMZ 64506 , 50.3 mm SL, Hakodate; HUMZ 202368 , 42.1 mm SL, HUMZ 202369 , 44.3 mm SL, HUMZ 232078 , 37.1 mm SL, HUMZ 232081 , 36.6 mm SL, HUMZ 232082 , 35.2 mm SL, HUMZ 232083 , 32.5 mm SL, Assabu ; KAUM –I. 139422, 37.5 mm SL, KAUM –I. 195100, 46.0 mm SL, KAUM –I. 195101, 41.8 mm SL, KAUM – I. 195102, 36.3 mm SL, Ebetsu, Ishikari-gawa River system; KAUM –I. 151258, 61.1 mm SL, KAUM –I. 151259, 50.9 mm SL, KAUM –I. 151260, 46.7 mm SL, KAUM –I. 151261, 43.4 mm SL, KAUM –I. 151961, 47.4 mm SL, KAUM –I. 151962, 34.8 mm SL, KAUM – I. 151963, 46.9 mm SL, Abashiri ; KAUM –I. 174720, 47.1 mm SL, KAUM –I. 174721, 44.8 mm SL, KAUM –I. 174722, 46.9 mm SL, KAUM – I. 174723, 46.7 mm SL, Ohzora ; KAUM – I. 174725, 51.7 mm SL, Kitami ; KAUM –I. 174735, 38.7 mm SL, KAUM – I. 174736, 51.2 mm SL, Shari ; KAUM – I. 174740, 50.9 mm SL, Shibetsu, Nemuro ; KAUM –I. 174756, 29.3 mm SL, KAUM –I. 174757, 35.5 mm SL, KAUM – I. 174758, 33.0 mm SL, Teshikaga ; KAUM –I. 216100, 46.3 mm SL, KAUM –I. 216101, 40.0 mm SL, KAUM –I. 216102, 32.6 mm SL, KAUM –I. 216103, 26.5 + mm SL, KAUM –I. 216104, 30.1 mm SL, KAUM –I. 216105, 28.9 mm SL, KAUM –I. 216106, 30.7 mm SL, KAUM –I. 216107, 28.7 mm SL, KAUM –I. 216108, 26.6 mm SL, KAUM –I. 216109, 26.3 + mm SL, KAUM –I. 216110, 40.3 mm SL, KAUM –I. 216111, 33.8 mm SL, KAUM –I. 216112, 34.2 mm SL, KAUM –I. 216113, 35.1 mm SL, KAUM –I. 216114, 27.5 mm SL, KAUM –I. 216115, 26.3 mm SL, KAUM –I. 216116, 24.9 mm SL, KAUM –I. 216117, 22.1 mm SL, KAUM – I. 216118, 22.0 mm SL, Chitose, Ishikari-gawa river system; KAUM –I. 216119, 54.9 mm SL, KAUM –I. 216120, 47.7 mm SL, KAUM –I. 216121, 47.9 mm SL, KAUM –I. 216122, 43.9 mm SL, KAUM –I. 216123, 45.8 mm SL, KAUM –I. 216124, 41.8 mm SL, KAUM –I. 216125, 40.6 mm SL, KAUM –I. 216126, 41.3 mm SL, KAUM –I. 216127, 40.0 mm SL, KAUM – I. 216128, 34.2 mm SL, Kushiro ; KAUM –I. 402600, 58.1 mm SL, KAUM –I. 402601, 51.6 mm SL, KAUM –I. 402602, 50.8 mm SL, KAUM – I. 402604, 53.9 mm SL, Akkeshi ; KPM-NI 2236 , 56.9 mm SL. Lake Kuccharo ; KPM-NI 3608 , 5 , 37.4–60.3 mm SL, Shibetsu, Kamikawa; KPM-NI 14502 , 2 , 26.3 and 27.9 mm SL, Teshikaga; KPM-NI 16626 , 31.7 and 34.2 mm SL, Nemuro ; KPM-NI 27043 , 64.0 mm SL, KPM-NI 29157 , 52.3 mm SL, Kuromatsunai; KPM-NI 31013 , 53.6 mm SL, Bihoro; KPM-NI 35304 , 51.2 mm SL, Oozora; KPM-NI 35305 , 58.3 mm SL, KPM-NI 35306 , 55.0 mm SL, KPM-NI 35307 , 43.8 mm SL, Shibetsu, Nemuro ; KPM-NI 38641 , 49.3 mm SL, Suttsu; NSMT-P 14346 , 34.5 mm SL, Urakawa; NSMT-P 34629 , 4 , 53.5–58.3 mm SL, Lake Kuccharo ; NSMTP 77400 , 7 , 38.2–44.6 mm SL, Fukagawa, Ishikari-gawa River System ; NSMT-P 90557 , 40.3 mm SL, Eniwa, Ishikari-gawa River System ; NSMT-P 91310 , 5 of 165, 49.1–58.7 mm SL, Abashiri ; NSMT-P 91315 , 49.7 mm SL, Teshikaga; NSMT-P 105454 , 45.2 mm SL, Kuromatsunai; NSMT-P SK 1769 , 2 , 38.5 and 39.8 mm SL, Chitose, Ishikari-gawa River System. Japanese Archipelago, Rebun Island : NSMT-P 11267 , 47.7 mm SL, NSMT-P 11270 , 75.7 mm SL, NSMT-P 11658 , 4 , 56.4–70.7 mm SL. Japanese Archipelago, Honshu Island : HUMZ 178293 , 55.2 mm SL, Oga, northern Akita ; KAUM –I. 168564, 37.2 mm SL, KAUM –I. 168565, 35.3 mm SL, KAUM –I. 168566, 40.6 mm SL, KAUM –I. 168567, 37.0 mm SL, KAUM –I. 168568, 39.7 mm SL, KAUM –I. 168569, 31.2 mm SL, KAUM –I. 168570, 30.6 mm SL, KAUM –I. 168571, 30.4 mm SL, KAUM –I. 168572, 30.7 mm SL, KAUM – I. 168573, 29.5 mm SL, Mutsu, Aomori ; KAUM –I. 168602, 43.2 mm SL, KAUM –I. 168603, 46.9 mm SL, KAUM –I. 168604, 42.1 mm SL, KAUM –I. 168605, 39.8 mm SL, KAUM – I. 168606, 38.9 mm SL, Noheji, Aomori ; KAUM – I. 401750, 46.6 mm SL, KAUM –I. 401751, 41.3 mm SL, KAUM –I. 401752, 45.5 mm SL, KAUM –I. 401753, 50.0 mm SL, KAUM –I. 401754, 47.7 mm SL, KAUM –I. 401755, 47.5 mm SL, KAUM –I. 401756, 49.5 mm SL, KAUM –I. 401757, 46.5 mm SL, KAUM –I. 401758, 44.7 mm SL, KAUM –I. 401759, 51.5 mm SL, KAUM –I. 401764, 57.0 mm SL, KAUM –I. 401765, 48.4 mm SL, KAUM –I. 401766, 50.9 mm SL, KAUM –I. 401767, 51.3 mm SL, KAUM – I. 401768, 47.1 mm SL, Yuza, Yamagata ; KAUM –I. 402613, 50.0 mm SL, KAUM –I. 402614, 54.1 mm SL, KAUM –I. 402615, 46.5 mm SL, KAUM –I. 402616, 45.6 mm SL, KAUM – I. 402617, 48.2 mm SL, Tsuruoka, Yamagata ; KAUM –I. 402620, 38.6 mm SL, KAUM –I. 402621, 40.8 mm SL, KAUM –I. 402622, 47.1 mm SL, KAUM –I. 402623, 48.6 mm SL, KAUM –I. 402702, 48.6 mm SL, KAUM –I. 402703, 40.9 mm SL, KAUM –I. 402704, 40.4 mm SL, KAUM –I. 402705, 39.9 mm SL, KAUM –I. 402706, 39.1 mm SL, KAUM – I. 402707, 32.3 mm SL, Shinjo, Yamagata ; KAUM –I. 402637, 39.6 mm SL, KAUM –I. 402638, 36.0 mm SL, KAUM – I. 402639, 30.1 mm SL, KAUM –I. 402640, 36.6 mm SL, KAUM –I. 402641, 40.3 mm SL, KAUM –I. 402642, 40.7 mm SL, KAUM –I. 402643, 38.6 mm SL, KAUM –I. 402644, 36.6 mm SL, KAUM –I. 402645, 33.6 mm SL, KAUM –I. 402646, 37.1 mm SL, KAUM –I. 402647, 44.5 mm SL, KAUM –I. 402648, 36.8 mm SL; KAUM –I. 402664, 41.7 mm SL, KAUM –I. 402665, 38.8 mm SL, KAUM –I. 402666, 47.8 mm SL, KAUM –I. 402680, 38.4 mm SL, KAUM –I. 402681, 41.5 mm SL, KAUM –I. 402682, 41.6 mm SL, KAUM –I. 402683, 42.5 mm SL, KAUM –I. 402684, 51.4 mm SL, KAUM –I. 402685, 38.5 mm SL, KAUM –I. 402686, 49.5 mm SL, KAUM –I. 402687, 42.5 mm SL, KAUM –I. 402688, 41.7 mm SL, KAUM –I. 402689, 43.1 mm SL, KAUM –I. 402690, 43.2 mm SL, KAUM –I. 402691, 50.1 mm SL, KAUM –I. 402692, 53.3 mm SL, KAUM –I. 402693, 42.9 mm SL, KAUM –I. 402694, 38.7 mm SL, KAUM –I. 402695, 46.1 mm SL, KAUM –I. 402696, 40.2 mm SL, KAUM –I. 402697, 39.2 mm SL, KAUM –I. 402698, 40.5 mm SL, KAUM –I. 402699, 38.3 mm SL, KAUM –I. 402700, 41.0

mm SL, KAUM –I. 402701, 44.0 mm SL, Yokote, southern Akita; KAUM –I. 402708, 44.4 mm SL, KAUM –I. 402709, 55.6 mm SL, KAUM –I. 402710, 35.8 mm SL, KAUM –I. 402711, 41.5 mm SL, KAUM –I. 402712, 41.2 mm SL, KAUM –I. 402713, 44.3 mm SL, Sakegawa, Yamagata; KPM-NI 3449, 54.3 mm SL, KPM-NI 3450, 54.0 mm SL, KPM-NI 3451, 50.7 mm SL, KPM-NI 3452, 42.7 mm SL, KPM-NI 4335, 44.6 mm SL, KPM-NI 4336, 45.8 mm SL, KPM-NI 4337, 43.7 mm SL, KPM-NI 4338, 33.6 mm SL, Murakami, Niigata; KPM-NI 3453, 39.0 mm SL, KPM-NI 3454, 35.1 mm SL, KPM-NI 3455, 34.4 mm SL, KPM-NI 3456, 34.4 mm SL, KPM-NI 3457, 3, 30.1–32.6 mm SL, KPM-NI 11364, 2, 40.0 and 43.6 mm SL, Nakajo, Niigata; KPM-NI 4339, 15, 33.3–45.1 mm SL, Niigata; KPM-NI 9835, 38.1 mm SL, KPM-NI 13336, 40.8 mm SL, Yuza, Yamagata; KPM-NI 71277, 38.3 mm SL, Takaoka, Toyama; NSMT-P 22115, 32.5–47.5 mm SL, Ishikawa; NSMT-P 29872, 6 of 45, 32.6–65.9 mm SL, Imizu, Toyama; NSMT-P 61184, 7, 18.5–48.1 mm SL, the Shimokita Peninsula, Aomori; NSMT-P 67619, 10, 43.3–53.7 mm SL, Echizen, Fukui; NSMT-P 76030, 25.9 mm SL, Hachiro-gata Lagoon, northern Akita; NSMT-P 77396, 4, 35.5–50.0 mm SL, Kanazawa, Ishikawa; NSMT-P 77402, 14, 23.6–32.5 mm SL, Murakami, Niigata; NSMT-P 77410, 5, 38.5 + – 51.4 mm SL, Niigata; NSMT-P 105204, 46.8 mm SL, Gosen, Niigata; NSMT-P 125386, 47.1 mm SL, Misawa, Aomori; NSMT-P SK 25695, 5, 37.5–47.5 mm SL, Echizen, Fukui; YCM-P 9537, 7, 39.3– 47.2 mm SL, Ohdate, northern Akita.

Diagnosis. Pungitius sinensis is distinguished from its congeners by the following combination of characters: dorsal-fin rays IX (VII–X) + 11 (9–12); anal-fin rays I + 10 (7–11); pectoral-fin rays 10 (9–11); pelvic-fin rays I + 2 (1 or 2); upper and lower procurrent caudal-fin rays both 5 (3–7), 10 (6–14) in total; lateral plates in a full (31–35 lateral plates from just above cleithrum to caudal-fin base) or incomplete row (0–7 lateral plates anteriorly, and 3–19 posteriorly from middle of anal fin), forming a distinct lateral keel on caudal peduncle; 7 (5–7) plates on ventral surface of caudal peduncle; vertebrae 32–36 (13–16 abdominal and 18–20 caudal vertebrae); dorsal-fin spines inclining alternately to sides of mid-line; first dorsal-fin spine anterodorsal to upper end of pectoral-fin base; ascending process of pelvis well-developed, upper end of pelvis reaching to level of fifth pectoral-fin ray base; antero-ventral process of ectocoracoid present, right and left ectocoracoids articulating anteriorly with each other; a distinct ridge on cleithrum and ectocoracoid; membranes of dorsal-fin spines hyaline or with some minute black spots; body dark green or dark yellow.

Description. Meristics and morphometrics in Table 1; selected frequency distributions of counts in Tables 2 and 3.

Body elongate, laterally compressed, tapering posteriorly to caudal peduncle; body depth greatest just before pelvic-fin origin.

Dorsal profile of head almost straight, gently ascending from mouth to dorsal fin origin; ventral profile slightly convex. Mouth small, oblique; anterior edge of upper jaw reaching to mid-pupil level, posterior end of jaw not reaching below anterior edge of eye. Eye large, rounded. Snout conical (lateral view), its length similar to eye diameter. Anterior nostril markedly smaller than posterior nostril; posterior nostril tubular, located slightly above mid-pupil level. Small conical teeth in 1–4 serial rows on both jaws, teeth absent on vomer and palatine.

Anus located just anterior to anal-fin spine. Ectocoracoid located on ventral aspect of pectoral girdle, curving antero-medially to articulate with opposite element; pelvic girdle articulating anteriorly with posterior end of ectocoracoid. Pelvis triangular (ventral view).

Dorsal-fin spines strong, sharply pointed, posteriormost spine longer than other spines in 268 specimens ( 71 specimens with last spine length similar to other spines); each spine accompanied posteriorly by triangular noninterconnected membrane. Two (1–3) plates on dorsum between top of head and dorsal-fin spine origin. Soft dorsal fin almost opposite to anal fin. Fin rays of dorsal and anal fins decreasing in length from second ray (first or third) to last ray. All soft rays of dorsal and anal fins branched (first and last few rays unbranched in few specimens).Anal-fin spine strong, sharply pointed, accompanied by triangular membrane. Pectoral-fin fan-shaped, all rays simple (rarely some rays branched). Pelvic-fin spine articulating with base of ascending process; dorsal edge of pelvic-fin spine with small serrations, anterior aspect of spine with many small tubercles. Caudal fin slightly rounded or bilobed, with 12 (10–13) principal rays.

Coloration in life and fresh specimens ( Fig. 2). Dorsal and lateral surfaces of head and body dark green (or dark yellow), with some indistinct dark blotches or stripes and numerous minute black spots; ventral surface of head and body white. All fin membranes almost hyaline ( Fig. 2D, E), sometimes some small black spots on dorsal-fin membrane ( Fig. 2 A–C). Breeding males with head and body black, and all fin membranes except for pelvic-fin spine hyaline ( Fig. 2 A, C). Pelvic fin membrane blue.

Coloration in preservative ( Fig. 3). Dorsal and lateral surfaces of head and body dark brown; ventral surface of head and body light brown. All fin membranes almost hyaline (some specimens retaining black spots on dorsal-fin membrane after several years of preservation).

Distribution. Pungitius sinensis has been recorded from northern China around the Bo-Hai Sea ( Liaoning to Shandong), Inner Mongolia, Anadyr (eastern north Russia), the Russian Far East around the Sea of Okhotsk ( Magadan, Shantar Islands, lower reaches of the Amur River, Kamchatka Peninsula and Sakhalin Island), Primorsky Krai, the Kuril Islands, the northern and eastern Korean Peninsula, and Hokkaido and the northern Honshu islands, Japan ( Ikeda 1933, 1935; Kim et al. 1989; Pietsch et al. 2001; Chereshnev 2002; Bogutskaya et al. 2008; Pichugin 2012; Ko 2016; Wang & Guo 2022; current study).

Remarks. Pungitius sinensis was originally described by Guichenot (1869) as Gasterosteus sinensis , based on seven specimens collected from China. Although Guichenot (1869) did not give a precise type locality, Berg (1907) and other authors (e.g., Bogutskaya et al. 2008) speculated that the syntypes were collected from the Yangtze River. However, the present study could not provide confirmed evidence of the syntypes being collected from the Yangtze River. In fact, previous studies from China (e.g., Bian et al. 2008; Zhou et al. 2018) also suggested that P. sinensis is not distributed in the Yangtze River. Guichenot (1869) suggested that the syntypes were donated by Armand David, a Lazarist missionary Catholic priest and naturalist, who at the time that Gasterosteus sinensis was described, had been collecting plant and animal specimens, primarily around Beijing and the Ordos Basin ( David 1875). Since P. sinensis inhabits the area around Beijing ( Wang 1984), the syntypes had likely been collected in that region.

Pungitius sinensis is distinguished from all other congeners by several characters, including fin ray numbers, presence of a distinct keel on caudal peduncle, and morphology of lateral plates, cleithrum, ectocoracoid, and pelvis (see also comparison of Pungitius sinensis and other congers). All syntypes of P. sinensis are in poor condition, making accurate counting of the soft rays of the dorsal, pelvic, and caudal fins (the anal-fin soft rays could be counted in only two of the seven syntypes, nine and 10 rays being observed) impossible. The dorsal-fin spines were relatively well preserved, there being nine spines in six of the syntypes and eight in the other. In two syntypes, the lateral plates could not be counted due to the damaged caudal peduncle. However, 32–34 lateral plates were counted along a continuous row in five other specimens. These meristic counts of the syntypes were within the ranges observed in the non-type specimens ( Table 1). Additional characters, such as a distinct keel on the caudal peduncle, distinct ridge on the cleithrum and ectocoracoid, the antero-ventral process of ectocoracoid, and well-developed ascending process of pelvis, were well preserved in the syntypes, and in the non-type specimens as well.

Guichenot (1869: pl. 12) provided an illustration of a single individual of G. sinensis , in which eight dorsal-fin spines are shown, a strong indication that that syntype with eight dorsal-fin spines ( 25.7 mm SL; Fig. 3A) was reproduced as Guichenot’s (1869) illustration.

Geographic variations. The present study revealed that specimens collected outside the Japanese Archipelago were armored with a full row of lateral plates, the exception being a single specimen from northern Sakhalin Island (HUMZ 158680, Piltum Bay), with an incomplete row of lateral plates. On the other hand, two phenotypes of P. sinensis were observed in the Japanese Archipelago; one phenotype with 31–35 lateral plates in a continuous row from just above the cleithrum to the caudal-fin base ( Fig. 1A), and the other with 3–19 lateral plates posteriorly on the body (often with 0–7 small lateral plates anteriorly) ( Fig. 1B, C), as shown in Takahashi et al. (2001). This suggests that the morphological diversity of lateral plates (full or incomplete row of lateral plates) in P. sinensis is a phenotypic variation found almost exclusively in populations inhabiting the Japanese Archipelago. No other morphological differences were observed between the populations possessing either full or incomplete row of lateral plates. Therefore, these differences in the lateral plates are regarded as intraspecific variations. Previous studies had suggested that inter-species and/or inter-population hybridizations in the past may have contributed to the diversification of lateral plates ( Takahashi et al. 2001; Wang et al. 2015; Guo et al. 2019).

The specimens collected from the Japanese Archipelago, Korean Peninsula, Primorsky Krai, and the Tym River (Sakhalin Island), usually had two pelvic-fin soft rays ( Fig. 4), as did specimens recorded from northern China ( Wang et al. 2022). However, specimens collected from elsewhere in Sakhalin Island, southern Kamchatka, and Liaoning, China have usually a single pelvic-fin soft ray ( Fig. 4). In addition, specimens of P. sinensis collected from near Magadan, northern Sea of Okhotsk have also been reported as having a single pelvic-fin soft ray ( Chereshnev 2002). Thus, it is clear that distinct geographic variations exist in the number of pelvic-fin soft rays. In addition, the pelvic-fin soft rays were branched in many specimens in the Japanese populations, but not so in the Sakhalin Island and Kamchatka populations.

Many specimens of P. sinensis examined in this study had nine dorsal-fin spines ( Fig. 5), though those from Lake Tunaicha (Sakhalin Island), Rebun Island, Urakawa, northern Akita ( Japan), and Liaoning ( China) frequently had ten spines ( Fig. 5). Kim et al. (1989) also reported that average numbers of dorsal-fin spines of P. sinensis collected from the Jusoochon and Ssangchon rivers in Kangwon-do, Korea were 8.7 (eight or nine; n = 50) and 8.5 (8–10; n = 17), respectively. Based on their study and data herein ( Fig. 5), the Korean population of P. sinensis had a relatively high proportion of individuals with eight dorsal-fin spines compared to populations in other regions.

No remarkable geographical variations in the numbers of pectoral-fin rays were apparent in the specimens of P. sinensis examined in this study (10 pectoral-fin rays in 293 of 323 specimens). However, Zhou et al. (2018) reported that a population of P. sinensis from Henan, China, had eight or nine pectoral-fin rays. Elsewhere, the number of pectoral-fin rays does not vary intraspecifically in most species of Pungitius (Keivany & Nelson 2000; Shedko et al. 2005; Matsumoto et al. 2021), though P. laevis has 10 or 11 pectoral-fin rays ( Denys et al. 2017).

Although no remarkable differences in the measurements were observed among specimens collected from various localities, those collected from Yamagata, Honshu Island, Japan, had a slightly greater ratio of caudal peduncle depth to caudal peduncle length than in specimens collected from other areas ( Fig. 6; Table 1). However, that proportion did not clearly distinguish the Yamagata population from other populations, the former therefore not being considered specifically distinct.

Comparisons of Pungitius sinensis and other congeners. Pungitius sinensis is easily distinguished from P. hellenicus , P. laevis , P. platygaster , and P. vulgaris (Maudyt 1849) by having a distinct keel on the side of caudal peduncle (vs. lacking a keel or presence of a thin keel in the latter four species) (Keivany & Nelson 2000; Denys et al. 2017). In addition, P. sinensis differs from P. hellenicus and P. platygaster by having 32–36 vertebrae (vs. 29–32 in the latter two species; Table 2) (Keivany & Nelson 2000; Esmaeili et al. 2023).

Pungitius sinensis is further distinguished from P. kaibarae , P. modestus , and P. polyakovi by having almost hyaline dorsal-fin spine membranes (vs. a black membrane in the latter three species) ( Shedko et al. 2005; Matsumoto et al. 2021). In P. modestus , even if such black membranes become faded in specimens preserved long-term in ethanol, the two species can be easily distinguished by the location of first dorsal-fin spine (usually anterodorsal to upper end of pectoral-fin base in P. sinensis vs. behind in P. modestus ). In addition, a distinct ridge is seen on the cleithrum as well as on the surface of the ectocoracoid in P. sinensis ( Fig. 7B, C) (vs. without ridges in P. modestus ). Pungitius sinensis is also easily distinguished from P. polyakovi , by the following characters; ascending process of pelvis well-developed, upper end reaching to fifth pectoral-fin ray base in P. sinensis ( Fig. 1) (vs. ascending process poorly-developed, upper end not reaching to fifth pectoral-fin ray base in P. polyakovi ); and antero-ventral process of ectocoracoid present in P. sinensis (vs. absent in P. polyakovi ) ( Shedko et al. 2005).

The morphology of Pungitius bussei has been poorly studied, making any comparisons difficult. However, Warpachowski (1888) stated that seven or eight anal-fin soft rays were observed in four syntypes of Gasterosteus bussei . Since P. sinensis has usually nine or ten anal-fin soft rays ( Table 2), the two species can probably be distinguished using this character.

Pungitius sinensis has been distinguished from P. pungitius by the morphology of lateral plates on the body, i.e. full row of lateral plates vs. incomplete row ( Berg 1907; Ikeda 1933; Tanaka 1982; Keivany & Nelson 2000). However, specimens of P. sinensis collected from several sites in the Japanese Archipelago did not possess any lateral plates anteriorly on the body, and could not be distinguished from P. pungitius using this character (which therefore cannot be considered as diagnostic for Japanese P. sinensis ). However, P. sinensis is distinguished from P. pungitius by (usually) having nine dorsal-fin spines (vs. 10) ( Table 2) and bright or dark green color on the body in life (vs. silver) ( Takata et al. 1987). The present study also revealed that P. sinensis differs from P. pungitius in the following characters: usually five procurrent caudal-fin rays each in the upper and lower caudal-fin lobes in P. sinensis vs. usually seven and six, respectively, in P. pungitius , and usually seven ventral plates on the caudal peduncle in P. sinensis vs. usually five in P. pungitius ( Fig. 8; Table 3). Further, the body color differs between the two species. In mature males during the breeding season, the body becomes black and the pelvic-fin membrane changes from hyaline to blue in P. sinensis ( Fig. 2A, C), whereas in P. pungitius only the ventral surface of the body becomes black, and the pelvic-fin membrane remains white ( Takata et al. 1987; Machida et al. 2022; current study). Keivany & Nelson (2000) stated that the number of pelvic-fin soft rays differentiates P. sinensis from P. pungitius (two vs. one). However, this character showed remarkable geographic variations ( Fig. 4), leading to the conclusion that pelvic-fin soft ray number is not diagnostic of P. sinensis , especially for specimens collected from Sakhalin Island and the Kamchatka Peninsula.

The taxonomy of P. stenurus has at no time been comprehensively studied, although Bogutskaya et al. (2008) briefly compared P. sinensis with P. stenurus (based on five syntypes of ZIN 2471), and distinguishing P. stenurus from P. sinensis by having a more elongate (vs. stout) body, slightly smaller lateral plates (vs. large plates), and silver body (vs. vertical dark bars on body). Based on a photograph of the syntypes of P. stenurus ( Matsumoto et al. 2021: fig. 7), the differences in lateral plate size noted by Bogutskaya et al. (2008) appear to fall within the range of intraspecific variation in P. sinensis examined here (e.g. HUMZ 236403, 56.2 mm SL, Fig. 3C). The preserved specimens of P. sinensis , being almost brown ( Fig. 3), differed from the silver-colored syntypes of P. stenurus . In addition, P. sinensis usually has nine dorsal-fin spines ( Table 2), compared with eight in P. stenurus ( Matsumoto et al. 2021) . Although P. sinensis is here considered distinct from P. stenurus , detailed studies are required to determine the taxonomic status of P. stenurus .

Pungitius sinensis is distinguished from P. tymensis by (usually) having nine (vs. 10–12) dorsal-fin spines ( Table 2). Pungitius sinensis is further differentiated from P. tymensis in its pelvic structure, well-developed (vs. poorly-developed) ascending process, its upper end reaching to level with fifth pectoral-fin ray base in P. sinensis (vs. usually not reaching to level with fifth pectoral-fin ray base in P. tymensis ) ( Fig. 1) (Keivany & Nelson 2000: fig. 4C; this study).

Synonymies. Gasterosteus wosnesenjenskyi was originally described by Kessler (1876), based on several specimens from western Kamchatka. Although Berg (1907) regarded this nominal species as valid (as a subspecies of P. sinensis ), subsequent studies (e.g., Berg 1949; Bogutskaya et al. 2008; Dyldin & Orlov 2017) regarded it as a junior synonym of P. sinensis . Our examination of the syntypes of G. wosnesenjenskyi (ZIN 2377 and 2378) revealed that it includes two distinct species. Seven syntypes registered as ZIN 2377 comprised two species, two specimens being P. sinensis , and five, P. pungitius . Similarly, nine syntypes registered as ZIN 2378 included six specimens of P. sinensis , and three of P. pungitius ( Fig. 9; Table 4). Kessler (1876) described G. wosnesenjenskyi as usually having a full row of lateral plates (33 or 34 plates), and rarely having an incomplete row. It is clear from the present study that the specimens with a full row of lateral plates are P. sinensis , and those with an incomplete row of lateral plates are P. pungitius . Although both species were included in the syntypes, G. wosnesenjenskyi is regarded herein as a junior synonym of P. sinensis , because the description of G. wosnesenjenskyi provided by Kessler clearly conforms to the characters of P. sinensis .

Steindachner (1881) described Gasterosteus japonicus based on a single specimen from Strelos Bay, near Vladivostok, Primorsky Krai. However, this name was a junior homonym of Gasterosteus japonicus Houttuyn 1782 ( Monocentridae : valid as Monocentris japonica ), and was subsequently replaced by Pygosteus steindachneri by Jordan & Snyder (1901). Jordan & Starks (1905) later regarded Pygosteus steindachneri as a junior synonym of G. sinensis , and subsequent studies followed that opinion (e.g., Okada 1961; Keivany & Nelson 2000).Although the syntypes of Gasterosteus japonicus Steindachner 1881 (MSNG 14075) were not examined during the present study, Steindachner’ s (1881) illustration clearly shows the dorsal-fin spine membranes as colorless, as seen in specimens of P. sinensis . Pungitius kaibarae , is also distributed in southern Primorsky Krai, the type locality of Gasterosteus japonicus Steindachner 1881 ( Shedko et al. 2005; Takahashi et al. 2016), but the specimen described by Steindachner (1881) was clearly identifiable as P. sinensis , based on the color of the dorsal-fin spine membrane.

Pygosteus brevispinosus was described by Otaki (1908), based on individuals from a collection site near Sapporo, Hokkaido Island, Japan (whereabouts of type specimens now unknown). Otaki (1908) described the lateral plate morphology as “the lateral pubic plate shorter and cun[e]iform”, being different from Pygosteus steindachneri (= Pungitius sinensis ), which has a full row of lateral plates. The term “shorter” used by Otaki (1908) probably referred to an incomplete row of lateral plates. As shown in this study, populations of P. sinensis with an incomplete row of lateral plates occur in the Japanese Archipelago, and the condition described by Otaki (1908) is included in the intraspecific variations of P. sinensis . In fact, a specimen of P. sinensis with an incomplete row of lateral plates (examined in this study) was collected from the Ishikari River basin near the type locality of Pygosteus brevispinosus . Therefore, Pygosteus brevispinosus is herein considered a junior synonym of P. sinensis .