Rhinogobius similis Gill, 1859

Maeda, Ken, Kobayashi, Hirozumi, Iida, Midori & Tran, Hau Duc, 2024, Taxonomy of freshwater gobies of the genus Rhinogobius (Oxudercidae, Gobiiformes) from central Vietnam, with descriptions of two new species, Zootaxa 5493 (5), pp. 507-541 : 532-536

Rhinogobius similis Gill, 1859

( Figs. 2 , 6i, j , 16–19 ; Tables 1 , 2 , 4–7 , 9 )

Rhinogobius similis Gill, 1859: 145 (original locality: Shimoda, Izu Province, Japan); Suzuki et al. 2016: 230 (redescription with neotype collected in Inouzawa River, Shimoda, Shizuoka Prefecture, Japan; published online in 2015 without page numbers).

Gobius giurinus Rutter, 1897: 86 (type locality: Swatow, coast of southeastern China).

Ctenogobius hadropterus Jordan & Snyder, 1901: 60 (type locality: Nagasaki, Japan).

Aboma tsinanensis Fowler, 1930: 30 (type locality: Da Ming Hu, Tsinan, China).

Ctenogobius lini Herre, 1934: 289 (type locality: Fu River at Wuchow, Kwangsi Province, China)

Ctenogobius giurinus : Wu & Ni 1986: 288 (Hainan, China); Luo 1989: 348 (Pearl River in Guangdong and Guangxi); Wu 1991: 480 (Guangdong).

Rhinogobius giurinus : Serov et al. 2006: 293; Wu & Zhong 2008: 594 ( China).

Rhinogobius longipinnis Nguyen & Vo in Nguyen, 2005: 636 (type locality: Nui Coc Lake , Dai Tu District, Thai Nguyen Province, Vietnam).

Material examined. Twenty-three specimens from Da Nang City , and one specimen from Thua Thien Hue Province, Vietnam. It was not always possible to confidently distinguish the sex of smaller individuals (<40 mm SL) .

HNUE-F 337–338 , 1 male (49.4 mm SL) and 1 female (44.0 mm SL), a stream north of Kim Lien Station, Lien Chieu District, Da Nang City (16°08’50.5”N 108°06’34.6”E), 3 March 2016 ; HNUE-F 339–340 , 1 female (43.0 mm SL) and 1 specimen of unknown sex (30.5 mm SL), Suoi Hoa, a tributary of Song Han, Hoa Vang District , Da Nang City (15°58’58”N 108°04’32”E), 4 March 2016 ; HNUE-F 341–342 , 1 male (42.5 mm SL) and 1 female (44.3 mm SL), Suoi Mo, a tributary of Song Han, Hoa Vang District , Da Nang City (16°00’01.3”N 108°03’33.2”E), 17 June 2019 ; NSMT-P 147883–147884 , 1 male (58.8 mm SL) and 1 female (50.9 mm SL), Suoi Mo, a tributary of Song Han, Hoa Vang District , Da Nang City (15°59’57.7”N 108°04’10.0”E), 1 March 2016 ; OISTICH 228–237, 2 males (47.4–67.1 mm SL), 4 females (45.2–62.4 mm SL), and 4 specimens of unknown sex (31.1–34.3 mm SL), Suoi Hoa, a tributary of Song Han, Hoa Vang District , Da Nang City (15°58’58”N 108°04’32”E), 4 March 2016 ; OISTICH 238, 1 male (58.0 mm SL), a stream north of Kim Lien Station, Lien Chieu District, Da Nang City (16°08’50.1”N 108°06’34.1”E), 25 January 2018 ; OISTICH 239, 1 male (50.5 mm SL), Suoi Mo, a tributary of Song Han, Hoa Vang District , Da Nang City (15°59’58.1”N 108°04’12.7”E), 27 January 2018 ; OISTICH 240–241, 1 male (56.3 mm SL) and 1 female (45.2 mm SL), Suoi Mo, a tributary of Song Han, Hoa Vang District , Da Nang City (16°00’01.3”N 108°03’33.2”E), 17 June 2019 ; OISTICH 242, 1 female (41.1 mm SL), a stream in Son Tra Peninsula, Son Tra District, Da Nang City (16°06’09.2”N 108°16’58.4”E), 19 June 2019 ; OISTICH 243, 1 male (59.7 mm SL), a tributary of Song Huong flowing along the border between Binh Thanh and Huong Tho , Huong Tra District , Thua Thien Hue Province (16°20’22.4”N 107°32’35.1”E), 21 June 2019 .

Description. Body nearly cylindrical anteriorly, and somewhat compressed posteriorly. Head depressed and eyes located dorsolaterally. Mouth terminal and oblique, with thick upper and lower lips. When mouth closed, anterior tip of upper jaw slightly protruding beyond lower jaw, or both jaws almost even. Mouth larger in males than females (upper-jaw length 12.6–17.6 vs. 10.9–12.2% of SL). Upper and lower jaws usually with 3–5 rows of conical teeth; those in outermost row enlarged and those in inner rows irregularly aligned. Mental flap on chin usually rectangular, trapezoidal (posterior end forming long side), or emarginate, and often with a small central projection. Anterior nostril short and tubular, posterior nostril a pore. Cephalic sensory pore system usually with B´, C, D(S), E, F, H´, K´, and L´ in oculoscapular canal and M´, N, and O´ in preopercular canal ( Fig. 16 ), but one specimen lacking pore C on left side, one specimen lacking pore N on right side, and one specimen having two pores F on both left and right sides. Arrangement of cutaneous sensory papillae of head shown in Fig. 16 . Cheek having several short transverse rows of papillae below eye and between two longitudinal rows across center of cheek. Vertebrae 10+16=26 (n=10; Table 1 ), P-V 3/II II I I 0/9 (n=10).

First dorsal fin with six spines, and second dorsal fin with one spine and eight soft rays ( Table 2 ). First and second dorsal-fin bases separated by a small interval (1.0–4.3% of SL). In females, first dorsal fin rounded, almost semi-circular; posterior tip of fin (tips of third to fifth spines) not reaching second dorsal-fin origin (n=4), just touching base of second dorsal-fin spine (n=1), exceeding base of second dorsal-fin spine, but not reaching base of first soft ray of second dorsal fin (n=1), or just touching base of first soft ray of second dorsal fin (n=1). In males, first dorsal fin rounded, but spines slightly more elongated than those on females; posterior tip of fin (tips of fourth to sixth spines) usually extending to, or exceeding second dorsal-fin origin and extending to base of second soft ray of second dorsal fin in two specimens. Anal fin with one spine and seven (n=1) or eight (n=23) soft rays ( Table 2 ). Caudal fin with 17 segmented rays including 12 (n=3), 13 (n=15), 14 (n=5), or 15 (n=1) branched rays; posterior margin rounded. Males having larger second dorsal and anal fins than females (second dorsal-fin length 31.3–43.7 vs 26.0–30.0% and anal-fin length 26.4–38.5 vs 23.7–28.2% of SL; Fig. 2 ). Pectoral fin with 17–20 rays (mode 19 rays) ( Table 4 ). Pelvic fin with one spine and five soft rays; pelvic fins joined together to form a cuplike disc with fleshy bilobed frenum.

Ctenoid scales covering lateral, dorsal, and ventral surfaces of body, except belly. Dorsal surface of nape and occipital region covered by cycloid and/or ctenoid scales; most or all of scales along predorsal midline cycloid usually in males, while more than half of them usually ctenoid in females and in small specimens of unknown sex; scaled area extending anteriorly to near posterior margin of eye in both males and females. Other regions on head naked. Belly and breast (pre-pelvic area) covered with cycloid scales. First and second dorsal-, and anal-fin bases covered with ctenoid scales, and a few small cycloid scales mixed in some specimens. A few cycloid scales also often mixed with ctenoid scales on flank behind pectoral fin. Proximal part of caudal fin covered with ctenoid scales and with a few cycloid scales. Presence of scales on pectoral-fin base unclear in many specimens (usually invisible without staining with alizarin red; see Suzuki et al. 2016), but a few cycloid scales sometimes visible. Longitudinal scales 29–32, transverse scales nine or ten, transverse scales on caudal peduncle seven, and predorsal scales 8–12 ( Tables 5–7 ).

Color in life and fresh ( Figs. 17 and 18 ): in males, background of head and body grey or yellowish-brown, and whitish ventral side. Head with many reddish-brown dots and lines forming many nearly parallel stripes running diagonally upward from anterior to posterior parts. An indistinct broad blackish band sometimes connecting middle of upper lip and anteroventral margin of eye, and also connecting posteroventral margin of eye and lower part of opercle. Pectoral-fin base with a black blotch on its upper part, and a white, transverse band. Dark-brown markings forming indefinite, bands and blotches on lateral and dorsal sides of body, often irregularly placed and uncountable. Scales on sides of body edged with orange, and each scale having a light blue (lower part) or white (dorsal part) center.

First and second dorsal fins orange or reddish-brown with many bluish-white spots, and with an orange margin and a yellow submarginal stripe. Caudal fin with a vertical blackish band on its base; 6–10 orange or reddish-brown vertical bands on middle part from base to tip, and their intervals bluish-white; an orange stripe running along dorsal margin and a yellow stripe below orange stripe. Anal fin reddish- or yellowish-brown, with a dark grey or dark orange margin. Pectoral fin translucent or greyish, but its lower proximal part pale yellow with a reddish-brown band dorsally on pale-yellow part. Pelvic disc yellowish translucent or grey.

In females, markings and background color of head and body similar to those in males, but females usually appear lighter colored than males Orange margin of scales on sides of body relatively inconspicuous. First and second dorsal fins translucent, with many reddish-brown and bluish-white spots alternately aligned along spines and soft-rays; distal parts reddish-brown translucent. Caudal fin similar to that of males, but without clear orange and yellow, dorsal stripes. Anal fin translucent with faint yellowish markings, and with dark-grey soft rays. Pectoral fin translucent, but its lower proximal part white, with a dorsal reddish-brown band. Pelvic disc yellowish translucent.

Color in preservative ( Fig. 6i, j ): background of head and body cream. Reddish-brown markings observed in life become dark brown. Orange, light blue, white, and yellow markings disappear, and those on fins become pale brown.

Remarks. Specimens from Da Nang have larger head length than those from northern Vietnam (in specimens larger than 40 mm SL, head length is 29.9–34.0 vs. 28.7–31.2% of SL), but smaller than those from Japan (vs. 32.1–35.5% of SL) ( Fig. 19 ). Although coloration of specimens from central and northern Vietnam are similar ( Figs. 9k, l and 17 ), these differ from Japanese populations. Vietnamese specimens usually lack the large black blotches on lateral side of the body, while Japanese specimens always have five, large black blotches along the lateral midline ( Figs. 9m –p and 17 ). A yellow longitudinal stripe on the second dorsal fin of the males is thinner in Vietnamese than in Japanese specimens. The ventral surface of the head in females is often black in Japanese specimens, especially in gravid individuals, but none of the Vietnamese specimens showed this black color. Ctenogobius hadropterus Jordan & Snyder, 1901 is a synonym of R. similis and its holotype collected in Nagasaki, Japan before 1901, also has distinct lateral blotches ( Fig. 20d ).

We did not observe fresh specimens of R. similis from China, but the type specimens of Ctenogobius lini Herre, 1934 , collected from Wuzhou, China in 1934, retain the distinct markings on head and fins, but lack the lateral blotches on their body ( Fig. 20a, b ). In the holotype of Gobius giurinus Rutter, 1897 , collected from Shantou, China before 1885, the presence of lateral blotches is unknown (because all markings are unclear although small melanophores are visible) ( Fig. 20c ), but the head is as small as in the specimens from northern Vietnam ( Fig. 19 ). These observations suggest that morphology of specimens from China is similar to those from Vietnam, but they are significantly different from R. similis from Japan (including type locality of R. similis ).

Rhinogobius similis has the widest distribution range among members of this genus, and it is found in continental regions spread across Korea, China from the northeast to south, and Vietnam, as well as on islands in Japan, Taiwan, and Hainan ( Suzuki et al. 2016). Those from Vietnam could be a different species from R. similis in Japan, but since determining their taxonomic status requires a comprehensive comparison of specimens from a wider distribution range, as well as a review of all nominal species currently considered synonyms of R. similis , we tentatively identify our Vietnamese specimens here as R. similis , following Suzuki et al. (2016).

Figures

FIGURE 2. Proportions of head length, upper-jaw length, first dorsal-, second dorsal-, anal-, and caudal-fin lengths to standard length (SL) of Rhinogobius rong (red circles), R. nami (light-blue circles), R. taenigena (deep-blue diamonds), R. leavelli (orange triangles), and R. similis (green squares) collected from Da Nang City and Thua Thien Hue Province. Solid symbols represent males, open symbols represent females, and symbols filled with grey represent specimens of unknown sex (for R. similis). Symbols with an asterisk are holotypes.

FIGURE 6. Preserved specimens of Rhinogobius rong (a, b), R. nami (c, d), R. taenigena (e, f), R. leavelli (g, h), and R. similis (i, j) collected from Da Nang City and Thua Thien Hue Province, Vietnam. Specimens on left side are males, right are females. a, NSMT-P 147886, holotype, 45.6 mm SL; b, OISTICH 254, paratype, 52.7 mm SL; c, NSMT-P 147890, holotype, 24.9 mm SL; d, OISTICH 290, paratype, 27.0 mm SL; e, OISTICH 299, 23.6 mm SL; f, OISTICH 305, 34.1mm SL; g, NSMT-P 147888, 43.8 mm SL; h, NSMT-P 147887, 41.1 mm SL; i, OISTICH 240, 56.3 mm SL; j, OISTICH 241, 45.2 mm SL.

FIGURE 9. Comparative material of the genus Rhinogobius from northern Vietnam (a–l) and Japan (m–p) observed in the present study. Photographs were taken immediately after fixation. Specimens on left side are males, right are females. a, b, R. sulcatus (a, OISTICH 184, 30.4 mm SL; b, OISTICH 190, 32.4 mm SL); c, d, R. boa (c, OISTICH 161, 25.4 mm SL; d, OISTICH 160, 28.0 mm SL); e, f, R. virgigena (e, NSMT-P 147872, 36.1 mm SL; f, OISTICH 154, 33.7 mm SL); g, h, R. variolatus (g, OISTICH 169, 31.4 mm SL; h, OISTICH 170, 28.8 mm SL); i, j, R. leavelli (i, OISTICH 209, 38.1 mm SL; j, OISTICH 210, 35.4 mm SL); k, l, R. similis (k, OISTICH 222, 54.4 mm SL; l, NSMT-P 147882, 44.7 mm SL); m, n, R. similis from Okinawa Island (m, URM-P 49149, 48.6 mm SL; n, OISTICH 2, 63.6 mm SL); o, p, R. similis, from Izu Peninsula (o, OISTICH 330, 47.6 mm SL; p, OISTICH 332, 51.0 mm SL).

FIGURE 16. Arrangement of cephalic sensory pores and cutaneous sensory papillae in Rhinogobius similis (OISTICH 228). a, lateral view; b, dorsal view; c, ventral view. AN, anterior naris; PN, posterior naris.

FIGURE 17. Rhinogobius similis from Da Nang City (a, b) and Thua Thien Hue Province (c) immediately after fixation. a, OISTICH 240, male, 56.3 mm SL; b, OISTICH 241, female, 45.2 mm SL; c, OISTICH 243, male, 59.7 mm SL.

FIGURE 18. In situ underwater photographs of Rhinogobius similis in Da Nang City, Vietnam. a, male, 12 January 2013; b, male, 4 March 2016; c, female, 4 March 2016; d, female, 12 January 2013 (photo by K. Maeda).

FIGURE 19. Relationships of head length and upper-jaw length to standard length (SL) in Rhinogobius similis collected from Da Nang City (light green squares) and Thua Thien Hue Province (orange square) in central Vietnam, Quang Ninh Province in northern Vietnam (red circles), Okinawa Island (light blue circles) and Izu Peninsula (deep blue diamonds) in Japan, holotype and paratypes of Ctenogobius lini Herre, 1934 from Wuzhou, China (deep green x), holotype of Gobius giurinus Rutter, 1897 from Shantou, China (pink x), and holotype of Ctenogobius hadropterus Jordan & Snyder, 1901 from Nagasaki, Japan (deep blue x). Solid symbols represent males, open symbols represent females, and those filled with grey represent specimens of unknown sex.

FIGURE 20. Type specimens of species currently considered synonyms of Rhinogobius similis Gill, 1859. a, b, CAS-SU 29089, possible types of Ctenogobius lini Herre, 1934 (a, 95.4 mm SL; b, 94.5 mm SL; one of them should be the holotype and the other is a paratype); c, CAS-SU 4990, holotype of Gobius giurinus Rutter, 1897 (63.0 mm SL); d, CAS-SU 6449, holotype of Ctenogobius hadropterus Jordan & Snyder, 1901 (45.3 mm SL).