Rhinogobius taenigena Chen, Kottelat & Miller, 1999

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 : 523-528

Rhinogobius taenigena Chen, Kottelat & Miller, 1999

( Figs. 2 , 6e, f , 10a–c , 11 , 12 ; Tables 1 , 2 , 4–7 , 9 )

Rhinogobius taenigena Chen, Kottelat & Miller, 1999: 29 (type locality: Xe Pon between rapids upstream and downstream of Ban Fuang, Xe Bang Hiang basin, Mekong basin, Savannakhet Province, Laos, 16°37‘06“N, 106°33‘30“E); Kottelat 2001b: 158–159 (Xe Bang Hiang basin, Laos); Serov et al. 2006: 295 (Gianh River basin to Phong Nha River, Quang Binh Province, Vietnam); Nagao Natural Environment Foundation 2021: 441 (Mekong basin in Savannakhet Province, Laos).

Material examined. Thirteen specimens from the Mekong basin and five specimens from the Song Huong (Perfume River) basin, both in Thua Thien Hue Province, Vietnam .

Mekong basin. HNUE-F 355–356 , 1 male (19.3 mm SL) and 1 female (29.5 mm SL), a tributary of Xe Kong in Hong Trung , A Luoi District (16°21’23.6”N 107°09’15.8”E), 20 June 2019 ; NSMT-P 147891–147892 , 1 male (28.1 mm SL) and 1 female (30.0 mm SL), a tributary of Xe Kong in Hong Trung , A Luoi District (16°21’23.6”N 107°09’15.8”E), 20 June 2019 ; OISTICH 291, 292, 294, 299, 1 male (23.6 mm SL) and 3 females (29.1–31.7 mm SL), a tributary of Xe Kong in Hong Trung , A Luoi District (16°21’23.6”N 107°09’15.8”E), 20 June 2019 ; OISTICH 301, male (29.7 mm SL), a tributary of Xe Kong in Hong Kim , A Luoi District (16°17’45.5”N 107°12’33.8”E), 20 June 2019 ; OISTICH 302–305, 2 males (30.8–34.9 mm SL) and 2 females (30.5–34.1 mm SL), a tributary of Xe Kong in Hong Kim , A Luoi District, (16°18’17.0”N 107°12’46.0”E), 20 June 2019 .

Song Huong basin. HNUE-F 357–358 , 1 male (29.4 mm SL) and 1 female (31.1 mm SL), a tributary of Song Bo in Hong Ha , A Luoi District (16°18’00.0”N 107°19’29.1”E), 20 June 2019 ; OISTICH 310–312, 1 male (28.8 mm SL) and 2 females (29.6–33.4 mm SL), a tributary of Song Bo in Hong Ha , A Luoi District (16°18’00.0”N 107°19’29.1”E), 20 June 2019 .

Description. Body nearly cylindrical anteriorly and somewhat compressed posteriorly. Anterior tip of head pointed in female, but rounded in male. Head larger in male than female (head length 30.9–33.5 vs. 28.1–30.5% of SL; Fig. 2 , Table 9 ). Eyes located dorsolaterally. Mouth terminal and oblique with thick upper and lower lips. When mouth closed, anterior tips of upper and lower jaws almost even, but lower jaw sometimes slightly protruding beyond upper jaw. Upper jaw extending posteriorly to about anterior margin of pupil. Mouth larger in male than female (upper-jaw length 10.2–14.6 vs. 8.5–9.6% of SL; Fig. 2 , Table 9 ). Upper and lower jaws usually with 2–4 rows of conical teeth; those in outermost row enlarged and those in inner rows irregularly aligned. Mental flap on chin usually rectangular or trapezoidal (posterior end forming long side), often with a small central projection. Anterior nostril short and tubular, posterior nostril a pore. Cephalic sensory pore system with B´, C, D(S), E, F, H´, K´, and L´ in oculoscapular canal and M´, N, and O´ in preopercular canal of both left and right sides in 11 of 18 specimens examined ( Fig. 10a–c ), but one specimen having an additional pore behind pore F (not G, but near F) on left side, two specimens having pore G on one side and pore H´ longitudinal groove-like on another side of one of two specimens, one specimen having an additional pore between pores E and F in right side, one specimen having a single heart-shaped pore C, two specimens having two pores aligned longitudinally on one side of C (total three pores at C) and oculoscapular canal of one side without pore M´ and with vertical groove-like N´ instead in one of two specimens, and oculoscapular canal of one side lacking N in another one. Arrangement of cutaneous sensory papillae of head shown in Fig. 10a–c . Cheek having no significant transverse papilla rows. Vertebrae 10+16=26 (n=1), 10+17=27 (n=11), 10+18=28 (n=1), or 11+17=28 (n=1; Table 1 ), P-V 3/II II I I 0/9 (n=12), P-V 3/II II I I I 0/10 (n=1), or 3/II III 0 I 0/9 (n=1).

First dorsal fin usually with six spines, but one specimen with seven spines. Second dorsal fin with one spine and seven (n=4), eight (n=11), or nine (n=3) soft rays ( Table 2 ). First and second dorsal-fin bases separated by a small interval (1.7–4.8% of SL; Table 9 ). In females, first dorsal fin rounded, almost semi-circular; posterior tip of fin (usually tips of sixth spines) not reaching second dorsal-fin origin. In males, first dorsal fin rounded or parallelogram; posterior tip of fin (usually fourth or fifth spine) extending to, or exceeding base of second dorsal-fin spine, but never exceeding base of second soft ray of second dorsal fin. Anal fin with one spine and six (n=2), seven (n=10), or eight (n=6) soft rays ( Table 2 ). Caudal fin with 17 segmented rays including 12 (n=3), 13 (n=2), 14 (n=12), or 15 (n=1) branched rays; posterior margin rounded. Males having larger second dorsal, anal, and caudal fins, than females (second dorsal-fin length 28.8–36.1 vs. 25.7–30.8% of SL, anal-fin length 25.0–33.0 vs. 22.0–28.4% of SL, and caudal-fin length 24.3–28.7 vs. 23.3–25.9% of SL; Fig. 2 , Table 9 ). Pectoral fin with 15–17 rays (mode 16 rays) ( Table 4 ). Pelvic fin with one spine and five soft rays; joined together to form a cuplike disc with fleshy bilobed frenum.

Ctenoid scales covering lateral, dorsal, and ventral surfaces of body posterior to flank except belly. Nape and posterior part of occipital region covered by cycloid scales; scaled area extending anteriorly to area above opercle both in males and females. Other regions on head naked. Belly and flank covered with cycloid scales. First and second dorsal, and anal-fin bases covered with ctenoid scales, and mixed with a few small cycloid scales. Proximal part of caudal fin covered with cycloid scales. Pectoral-fin base and breast (pre-pelvic area) probably naked (at least invisible without staining with alizarin red; see Suzuki et al. 2016). Longitudinal scales 30–33 (usually 31 or 32), transverse scales 8–10, transverse scales in caudal peduncle usually seven but six in a single specimen, and predorsal scales 5–12 ( Tables 5–7 ).

Color in life and fresh ( Figs. 11 and 12 ): in males, background of head and body grey or yellowish-brown, but whitish on ventral side. Reddish-brown stripe connecting posterior margin of center of upper lip and anterior margin of left and right eyes; thinner and unclear stripe continuing posteriorly from posterior margin of eye, but ending immediately and not reaching posterior margin of preopercle. No or faint reddish-brown marking at center of upper lip. Dorsal side of head often darker than lateral side. Lower half of cheek and opercular region often darker than upper half. Opercular membrane, interopercle, and lower part of subopercle light bluish-grey with many small red or orange spots. Six to eight, dark-brown transverse bands regularly aligned along lateral side of body from flank to caudal-fin base, and intervals light blue, but this pattern sometimes irregular and unclear. Many small, orange spots sometimes scattered on sides of body.

First dorsal-fin with series of black or reddish-brown markings on middle parts of membranes between first to fifth spines; anterior two markings (between first and second, and second and third spines) usually black and clear, but posterior ones reddish-brown and often unclear. Distal part of membrane light blue or white between first and second spines, and orange or red between second and fifth spines. Distal parts of spines black or grey. Reddish-brown spots on proximal part of first to fourth spines; spines and membranes light bluish-grey, both above and below reddish-brown spots. Membranes posterior to fifth spine light bluish-grey with some reddish-brown spots. Second dorsal-fin reddish-brown with four to seven light bluish-grey stripes across fin, and with a broad, orange or pale-yellow band at distal margin. A black, vertical rectangular or elliptical spot at middle proximal part of caudal fin, with a yellowish-brown or grey blotch above black spot, but this blotch often unclear. Other part of caudal fin yellowish or greyish translucent with five or six reddish-brown vertical bands with a pale-yellow margin ( Fig. 11b ), or dusky grey or reddish-brown with a pale-yellow margin without distinct vertical bands ( Fig. 11a ). Anal fin orange, but dark brown distally with broad, bluish-white margin. Pectoral fin grey or greyish translucent, its proximal part pale yellowish-brown or pale grey with a black spot at middle of base; an additional black spot often appearing at lower part of pectoral-fin base, which is sometimes combined with middle one forming a large black blotch. Pelvic disc dark grey with a white or light blue margin.

In females, markings and background color of head and body similar to those of males, but opercular membrane, interopercle, and lower part of subopercle yellowish-brown or dark grey without red spots. First dorsal fin having two to four, indefinite brown stripes; intervals translucent or white; distal part of fin yellow or bluish-white. Second dorsal fin with four to five, brown stripes, intervals white or translucent; with a yellow or bluish-white margin. Caudal fin translucent or white with five or six brown bands with a thin, pale-yellow margin; color and markings of proximal part of fin similar to those in males. Anal fin translucent, but reddish-brown or dark brown distally with a bluish-white margin. Pectoral fin translucent with a pattern on its base similar to that in males. Pelvic disc translucent or grey with a white margin.

Color in preservative ( Fig. 6e, f ): background of head and body cream and those of fins translucent or light brown. Reddish-brown markings observed in life become dark brown, and dusky-brown markings become black. Light bluish-grey color on opercular membrane, interopercle, and lower part of subopercle of male become dark brown, and red and orange spots become light brown (dark and pale pattern opposite from that in life). Red, orange, white, and bluish colors of fins disappeared.

Remarks. The type locality of R. taenigena is Xe Pon (Se Pon), a tributary of the Banghiang River in the Mekong basin ( Chen et al. 1999). Though located in Laos, it is close to the border with Vietnam (a little downstream from the Xe Pon reaches shown in Fig. 1 ). This species was also reported from Quang Binh Province ( Fig. 1 ) in Vietnam from the Gianh River basin to Phong Nha River ( Serov et al. 2006). We found this species in two river systems in Thua Thien Hue Province of Vietnam ( Fig. 1 ). One of them, Xe Kong (Se Kong), is a tributary of the Mekong, originating in Thua Thien Hue Province and flowing through southern Laos and eastern Cambodia. It joins the Mekong near Stung Treng, Cambodia.Another site is in the upper reaches of the Song Bo (Bo River), a tributary of the Song Huong (Perfume River), which flows directly to the South China Sea near the city of Hue. These suggest that this species could be widely distributed in river systems near the Vietnam-Laos border in this region.

Chen et al. (1999) described “four small blackish-brown spots on ventral edge of cheek” (on the ventral margin of the preopercle according to their fig. 16) of a male as a diagnostic character of R. taenigena . They described the coloration based on “observations from color slides taken of freshly preserved specimens.” Nagao Natural Environment Foundation (2021) noted that “the spots are not always evident” in specimens freshly collected near the type locality, and “if present, the number varies from one to four.” Photographs by the Nagao Natural Environment Foundation (2021: 441) show orange spots similar to spots on the opercular membrane, interopercle, and lower part of subopercle. Our material from Vietnam has neither blackish-brown spots nor spots of any other color on the preopercle, either in fresh or after preservation. This is the only point on which our observations do not agree with previous descriptions. No significant morphological differences were also found between the Xe Kong and Song Bo populations.

Figures

FIGURE 1. Map of South East Asia showing Vietnam, the Mekong and the Red River basins (left), and collection sites for Rhinogobius in Da Nang City and Thua Thien Hue Province in central Vietnam (orange dashed circles, right). Symbols below or above orange dashed circles indicate the occurrence of R. rong (red circles), R. nami (light blue circle), R. taenigena (deep blue diamonds), R. leavelli (orange triangles), and R. similis (green squares) at their respective locations.

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 10. Arrangement of cephalic sensory pores and cutaneous sensory papillae in Rhinogobius taenigena (a–c, OISTICH 303) and Rhinogobius leavelli (d–f, NSMT-P 147888). a, d, lateral view; b, e, dorsal view; c, f, ventral view. AN, anterior naris; PN, posterior naris.

FIGURE 11. Rhinogobius taenigena immediately after fixation. a, OISTICH 303, male, 30.8 mm SL; b, OISTICH 312, male, 28.8 mm SL; c, OISTICH 304, female, 30.5 mm SL; d, OISTICH 311, female, 33.4 mm SL.

FIGURE 12. In situ underwater photographs of Rhinogobius taenigena in the upper reaches of Xe Kong (Mekong basin) in Thua Thien Hue Province, Vietnam. a, b, males, 20 June 2019; c, d, females, 20 June 2019 (photo by K. Maeda).