Rhinogobius nami, Maeda & Kobayashi & Iida & Tran, 2024

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 : 518-521

Rhinogobius nami , sp. nov.

( Figs. 2 , 3d–f , 6c, d , 7 , 8 ; Tables 1–7 )

Holotype. NSMT-P 147890 , male (24.9 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.

Paratypes. HNUE-F 351–352 , 1 male (27.2) and 1 female (24.8 mm SL), Suoi Mo, a tributary of Song Han , Hoa Vang District (15°59’58.1”N 108°04’12.7”E) , 27 January 2018; HNUE-F 353–354 , 1 male (25.1) and 1 female (28.7 mm SL), same data as holotype ; NSMT-P 147889 , female (32.4 mm SL), same data as holotype ; OISTICH 272–273, 1 male (26.9 mm SL) and 1 female (27.5 mm SL), Suoi Mo, a tributary of Song Han , Hoa Vang District (15°59’57.7”N 108°04’10.0”E) , 1 March 2016; OISTICH 274–275, 1 male (27.5 mm SL) and 1 female (30.6 mm SL), Suoi Hoa , a tributary of Song Han, Hoa Vang District (15°57’20.2”N 107°58’16.4”E) , 2 March 2016; OISTICH 276–278, 3 females (28.0– 29.3 mm SL), Suoi Mo, a tributary of Song Han , Hoa Vang District (15°59’58.1”N 108°04’12.7”E) , 27 January 2018; OISTICH 279, female (26.8 mm SL), Suoi Hoa, a tributary of Song Han , Hoa Vang District (15°57’20.2”N 107°58’16.4”E) , 27 January 2018; OISTICH 280–290, 3 males (25.3–28.3 mm SL) and 8 females (27.0– 30.6 mm SL), same data as holotype .

Diagnosis. Pectoral fin with 14–16 rays. Second dorsal and anal fins usually with one spine and eight soft rays. Number of vertebrae usually 26. Nape and posterior part of occipital region covered by cycloid scales; scaled area extending anteriorly to about halfway between posterior margins of preopercle and opercle. Longitudinal scales 28–31, transverse scales eight or nine, and predorsal scales 6–11. Cephalic sensory pore system usually with B´, C, D(S), E, F, H´, K´, L´, M´, N, and O´. Five, longitudinal, reddish-brown or dusky-brown stripes (dotted lines) running from trunk to caudal peduncle both in male and female; fourth (from dorsal) one slightly below lateral midline most distinct and others sometimes unclear. Male having three parallel, diagonally downward, reddish-brown or dusky-brown stripes on ventral part of cheek. Opercular membrane, interopercle, and lower part of subopercle of live male specimen light bluish-grey with many red or orange spots.

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 31.3–34.5 vs. 28.4–30.9% of SL; Fig. 2 , Table 3 ). 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 or lower jaw protruding slightly beyond upper jaw. Upper jaw extending posteriorly to center of eye in male, but ending below anterior part of eye (between anterior margin of eye and anterior margin of pupil) in female. Mouth larger in male than female (upper-jaw length 11.6– 13.8 vs. 8.4–9.6% of SL; Fig. 2 , Table 3 ). 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 round or rectangular, often with a small central projection. Anterior nostril short 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 20 of 25 specimens examined (including holotype; Fig. 3d–f ), but three specimens having pore G in one or both side(s), and two specimens having an additional pore behind pore F (not G, but near F) in one or both side(s). Arrangement of cutaneous sensory papillae of head shown in Fig. 3d–f . Cheek having no significant transverse row of papillae. Vertebrae 10+15=25 (n=1) or 10+16=26 (n=13; Table 1 ), P-V 3/II II I I 0/9 (n=14).

First dorsal fin usually with six spines, but one specimen with five. Second dorsal fin usually with one spine and eight soft rays, but three specimens with one spine and seven soft rays ( Table 2 ). First and second dorsal-fin bases separated by a small interval (2.8–5.8% of SL; Table 3 ). In female, first dorsal fin rounded, almost semi-circular; posterior tip of fin (tips of fourth to sixth spines) not reaching second dorsal-fin origin. In male, first dorsal fin in parallelogram shape; posterior tip of fin (usually fourth spine) extending to, or exceeding base of second dorsal-fin spine, but never reaching base of second soft ray of second dorsal fin. Anal fin with one spine and seven (n=4) or eight (n=21) soft rays ( Table 2 ). Caudal fin with 17 segmented rays including 12 (n=15), 13 (n=9), or 14 (n=1) branched rays; posterior margin rounded. Male having larger second dorsal, anal, and caudal fins than female (second dorsal-fin length 31.2–37.5 vs. 25.0–28.3% of SL, anal-fin length 27.6–30.1 vs. 23.5–27.2% of SL, and caudal-fin length 26.5–29.6 vs. 21.8–26.6% of SL; Fig. 2 , Table 3 ). Pectoral fin with 14–16 rays (mode 15 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 posterior to flank except belly. Nape and posterior part of occipital region covered by cycloid scales; scaled area extending anteriorly around middle between posterior margin of preopercle and posterior margin of opercle both in male and female. Other regions of head naked. Belly and flank covered with cycloid scales. First and second dorsal, and anal-fin bases covered with ctenoid scales and a few small cycloid scales mixed. Proximal part of caudal fin covered with cycloid scales. Scales on breast (pre-pelvic area) difficult to detect, but cycloid scales observed in a few individuals. Pectoral-fin base probably naked (at least invisible without staining with alizarin red; see Suzuki et al. 2016). Longitudinal scales 28–31, transverse scales eight or nine, transverse scales in caudal peduncle seven, and predorsal scales 6–11 ( Tables 5–7 ).

Color in life and fresh ( Figs. 7 and 8 ): in male, background of head and body cream or yellowish-brown, but whitish on ventral side. A clear, reddish-brown stripe across center of upper lip; stripe splitting to left and right sides at snout and extending to anterior margin of eyes and continuing posteriorly from posterior margin of eye to region above gill opening, but posterior half indistinct. Dorsal side of head above this stripe, grey or brown. Lower half of cheek and opercular region darker than upper half, sometimes strongly contrasting. Reddish-brown or dusky-brown spot at posterior part of upper lip. Three parallel, diagonally downward, reddish-brown or dusky-brown stripes on ventral part of cheek. Opercular membrane, interopercle, and lower part of subopercle light bluish-grey with many red or orange spots. Posterior part of lower lip also often light bluish-grey. Five longitudinal, reddish-brown or dusky-brown stripes (formed by dotted lines) running on lateral and dorsal sides from trunk to caudal peduncle; fourth one (counted from dorsal) slightly below lateral midline being most distinct and others sometimes unclear. Three to six indefinite dusky transverse bands sometimes appearing on lateral side of body.

First dorsal fin with series of black or dusky-brown markings on middle parts of membranes between first to fifth spines; marking between first and second spines largest and clearest, and posterior ones sometimes unclear. Distal part of membrane light blue or white between first and second spines, and orange or red between second and fifth spines. Distal part of spines black or grey. Reddish-brown spots on proximal part of first to fourth spines; spines and membranes white between proximal reddish-brown spots and middle black or dusky-brown markings. Two or three indefinite reddish-brown stripes on membranes posterior to fifth spine and white between stripes (in most specimens, as in Fig. 8a , but stripes sometimes disordered, as in Fig. 7a ). Second dorsal fin with three to six reddish-brown spots aligned along each spine and soft rays; membrane around these spots also reddish-brown and forming stripes across fin. Proximal and middle parts of spine, soft rays, and membranes white between reddish-brown spots. Distal margin of second dorsal fin white or light blue. Black, vertical rectangular or elliptical spot surrounded by cream and orange at middle of proximal part of caudal fin. Remainder of caudal fin white or translucent with many reddish-brown spots forming five to eight vertical bands, but ventral part orange or dark brown. Anal fin orange, but dusky brown distally with bluish-white margin. Pectoral fin greyish translucent or grey, but its proximal part light yellowish-brown or light grey with large black or reddish-brown blotch at middle of pectoral-fin base. Pelvic disc greyish translucent or dark grey with white or light blue margin.

In female, markings and background color of head and body similar to those of male, but lacking three parallel, diagonally downward stripes from ventral part of cheek. Opercular membrane, interopercle, lower part of subopercle, and posterior part of lower lip yellowish-brown or dark grey without red spots. First dorsal fin translucent with one to five indefinite reddish-brown spots along each spine; proximal parts of spines white between reddish-brown spots; distal part of fin yellow. Markings and background of second dorsal, caudal, and pectoral fins similar to those of male, but white margin of second dorsal fin thinner and often indistinct, and ventral part of caudal fin translucent instead of orange. Anal fin translucent, but reddish or dark brown distally with thin, bluish-white margin. Pelvic disc translucent with white margin.

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

Etymology. The specific name of the new species is dedicated to the late Chu Hoang Nam, who helped our surveys in Vietnam during 2018 and 2019.

Comparison. Rhinogobius nami shares many morphological features with R. sangenloensis Chen & Miller, 2014 from Hainan, China. The coloration is nearly identical, including the longitudinal stripes on body and fin markings, but the male of new species has three reddish-brown or dusky-brown stripes on cheek (absent in R. sangenloensis ; Chen & Miller 2014), and the mode count of pectoral-fin rays is also different (15 in R. nami vs. 17 in R. sangenloensis ; Chen & Miller 2014). Both males and females of R. nami have a black, vertical rectangular or elliptical spot at the middle of caudal-fin base, while R. sangenloensis female has a black horizontal bar ( Chen & Miller 2014).

The three oblique stripes on the cheek of male specimens of R. nami is one of the features of the new species. Several Chinese and Vietnamese species of the genus also have oblique stripes on the cheek. The new species however differs from most of these species having a thinner and/or more numerous stripes (in R. changtinensis Huang & Chen, 2007 , R. lingtongyanensis Chen, Wang, Chen & Shao, 2022 , R. longyanensis Chen, Cheng & Shao, 2008 , R. lungwoensis Huang & Chen, 2007 , R. rubrolineatus Chen & Miller, 2008 , R. sagittus Chen & Miller, 2008 , and R. wangi Chen & Fang, 2006 ) ( Chen & Fang 2006; Chen & Miller 2008; Chen et al. 2008, 2022a; Huang & Chen 2007) ( Table 8 ).

Male of R. sulcatus Chen & Kottelat, 2005 has three broad stripes similar to those of the new species, but the stripes are longer (often reaching upper half of cheek) ( Fig. 9a ), and often branched and connected with each other, forming a reticulate pattern. Rhinogobius sulcatus also differs from the new species in lacking longitudinal, reddish-brown or dusky-brown stripes on sides of the body ( Fig. 9a, b ) (five stripes in male and female of R. nami ; Fig. 7a, b ), seven soft rays on anal fin (vs. usually eight in R. nami ; Table 2 ), 16 pectoral-fin rays (vs. 15; Table 4 ), and 27 vertebrae (vs. 26; Table 1 ).

Males of R. duospilus (Herre, 1935) , R. ponkouensis Huang & Chen, 2007 , and R. virgigena Chen & Kottelat, 2005 , have two or three stripes on cheek, but lack the longitudinal stripes along sides of the body ( Herre 1935a; Wu & Ni 1986; Wu 1991; Chen & Kottelat 2005; Huang & Chen 2007; Wu & Zhong 2008; observation on R. virgigena in the present study; Fig. 9e, f ) (vs. five stripes in R. nami ; Fig. 7a, b ), 27 and 28 vertebrae in R. duospilus and R. ponkouensis , respectively ( Huang & Chen 2007) (vs. usually 26 in R. virgigena and R. nami ; Table 1 ).

Among species from central Vietnam described in the present study, R. nami is most similar to R. taenigena , sharing the same markings on fins, and the red and light bluish-grey patterns on opercular membrane, interopercle, and lower part of subopercle of the male ( Figs. 7a and 11a, b ). However, R. nami can be distinguished from R. taenigena in the presence of five longitudinal stripes on sides of the body (absent in R. taenigena ), three oblique stripes on the male’s cheek (vs. absent) and presence of 26 vertebrae (vs. 27; Table 1 ).

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 3. Arrangement of cephalic sensory pores and cutaneous sensory papillae in Rhinogobius rong (a–c, NSMT-P 147886) and Rhinogobius nami (d–f, NSMT-P 147890). a, d, lateral view; b, e, dorsal view; c, f, ventral view.AN, anterior naris; PN, posterior naris.

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 7. Rhinogobius nami immediately after fixation. a, NSMT-P 147890, holotype, male, 24.9 mm SL; b, OISTICH 282, paratype, female, 26.6 mm SL.

FIGURE 8. Live images of Rhinogobius nami in aquarium (a) and in situ underwater footage from Da Nang City, Vietnam (b–d). a, male, 12 January 2013; b, male, 13 January 2013; c, d, females, 13 January 2013 (photo by K. Maeda).

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 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.