Rhinogobius rong, 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 : 509-517

Rhinogobius rong , sp. nov.

( Figs. 2 , 3a–c , 4 , 5 , 6a, b ; Tables 1–7 )

Holotype. NSMT-P 147886 , male (45.6 mm SL), Suoi Hoa, a tributary of Song Han, Hoa Vang District , Da Nang City (15°57’60.0”N 108°01’44.2”E), 2 March 2016.

Paratypes. HNUE-F 343 , female (41.4 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 344 , female (47.5 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 ; HNUE-F 345 , male (30.4 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 ; HNUE-F 346 , male (43.3 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 ; NSMT-P 147885 , female (39.2 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 244–248, 1 male (43.1 mm SL) and 4 females (37.0– 38.7 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 ; OISTICH 249–251, 1 male (60.0 mm SL) and 2 females (33.1–42.6 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 252, female (42.6 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 253–254, 1 male (32.9 mm SL) and 1 female (52.7 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 255, female (46.1 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 .

Diagnosis. With mouth closed, anterior tip of lower jaw protruding significantly beyond upper jaw in larger males (> 40 mm SL). Pectoral fin with 18–20 rays (usually 19). Second dorsal, and anal fin 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 posterior margin of preopercle. Longitudinal scales 31–34, predorsal scales 11–17. Cephalic sensory pore system usually with B´, C, D(S), E, F, H´, K´, L´, M´, N, and O´. Cheek with four longitudinal rows of cutaneous sensory papillae and no transverse row. Two broad, diagonally downward orange stripes, and one or two large orange spot(s) on cheek of living males; thinner and reddish-brown or grey similar markings in females.

Description. Body nearly cylindrical anteriorly and somewhat compressed posteriorly. Head depressed and larger in large males (> 40 mm SL) than females (head length 31.9–35.8 vs. 28.2–31.7% of SL; Fig. 2 ). Eyes located dorsolaterally. Mouth terminal and oblique with thick upper and lower lips. With mouth closed, anterior tip of lower jaw protruding significantly beyond upper jaw in large males (> 40 mm SL), and upper and lower jaws almost even in females, and two smaller males (30.4- and 32.6-mm SL). Posterior end of upper jaw exceeding anterior margin of eye. Mouth larger in large males (> 40 mm SL) than females (upper-jaw length 12.2–16.5 vs. 9.9–11.6% of SL; Fig. 2 ), and end of upper jaw reaching middle of eye in larger males. Upper and lower jaws usually with 3–4 rows of conical teeth; those on outermost row enlarged and those on inner rows irregularly aligned. Mental flap on chin bilobed ( Fig. 3c ), rounded rectangular, or trapezoidal (posterior end forming long side). 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 nine of 18 specimens examined (including holotype; Fig. 3a–c ), but one specimen with single Y-shaped pore C and longitudinal groove-like pore D, one specimen with additional pore behind pore F of left oculoscapular canal, one specimen having pore G in left oculoscapular canal, three specimens lacking pores N in one preopercular canals (either left or right), two specimens lacking pore N in both preopercular canals, and one specimen having only pore O´ in right preopercular canal. Arrangement of cutaneous sensory papillae of head shown in Fig. 3a–c . Cheek having four longitudinal rows of papillae and no transverse row. Vertebrae 10+15=25 (n=1) or 10+16=26 (n=12; Table 1 ), P-V 3/II II I I 0/9 (n=8).

First dorsal fin with six spines. Second dorsal fin usually with one spine and eight soft rays, but two specimens with one spine and seven soft rays ( Table 2 ). First and second dorsal-fin bases separated by a small space (1.3–3.5% of SL; Table 3 ). First dorsal fin rounded, usually almost semi-circular; posterior tips of fin (usually tips of fourth to sixth spines) not reaching second dorsal-fin origin (in ten smaller males and ten females), touching base of second dorsal-fin spine (two males and two females), or exceeding base of second dorsal-fin spine, but not reaching base of first soft ray of second dorsal fin (two males). Anal fin with one spine and eight soft rays ( Table 2 ). Caudal fin with 17 segmented rays including 14 branched rays, except one specimen with 18 segmented rays including 16 branched rays; posterior margin rounded. Large males (> 40 mm SL) having larger second dorsal, anal, and caudal fins than females (second dorsal-fin length 30.3–36.5 vs. 25.9–29.3% of SL, anal-fin length 27.0–30.6 vs. 24.6–26.6% of SL, and caudal-fin length 25.4–28.1 vs. 22.5–25.7% of SL; Fig. 2 ). Pectoral fin with 18–20 rays (usually 19) ( Table 4 ). Pelvic fin with one spine and five soft rays. Pelvic fins joined to form cuplike disc with fleshy bilobed frenum.

Ctenoid scales covering lateral, dorsal, and ventral surfaces of body except nape and belly. Dorsal surface of nape and posterior part of occipital region covered by cycloid scales, but four specimens (three females and one smaller male) with a few ctenoid scales along dorsal midline near first dorsal-fin origin; scaled area extending anteriorly to around posterior margin of preopercle, or slightly anterior to this point in males, and around this point or little posterior to this point, in females. Sides of posterior occipital region and nape covered with ctenoid scales. Other regions of head naked. Belly and breast (pre-pelvic area) covered with cycloid scales. First and second dorsal, and anal-fin bases covered with ctenoid scales, sometimes with a few small cycloid scales interspersed. A few cycloid scales also interspersed with ctenoid scales on flank behind pectoral fin and on proximal part of caudal fin. Pectoral-fin base usually naked (at least invisible without staining with alizarin red; see Suzuki et al. 2016), but 1–2 cycloid scale(s) sometimes visible. Longitudinal scales 31–34, transverse scales 10–12 (usually 10), transverse scales on caudal peduncle 7–9, and predorsal scales 11–17 ( Tables 5–7 ).

Color in life and fresh ( Figs. 4 and 5 ): in male, background of head and body greenish or yellowish-grey, but whitish on ventral side. An orange stripe connecting snout tip and anterior margin of eye; this stripe continuing posteriorly from posterior margin of eye to region above gill opening. Faint orange stripe running horizontally below eye to opercle; often intermittent. Broad, diagonally downward orange stripe running from above middle of upper lip to cheek (sometimes intermittent); another short, orange stripe running above posterior end of upper lip parallel to broad stripe; one or two large orange spot(s) on cheek posterior to broad stripe. Broad, orange stripe running almost horizontally (but slightly diagonally upward) along middle of opercle and subopercle; extending posteriorly on pectoral-fin base, where it being darker. Opercular membrane, interopercle, and lower part of subopercle with light orange or yellow markings arranged almost horizontally. Six indistinct dusky-grey blotches and five indistinct cream bands between them sometimes appearing laterally on body from flank to caudal peduncle. Many orange spots scattered on lateral and dorsal sides of body and dorsal side of head.

First dorsal fin greyish translucent, with a black spot just below middle on membrane between first and second spines; upper part of this spot bluish. Some orange markings aligned along proximal part of fin and on middle to distal parts of fourth, fifth, and sixth spines. Distal part of fin yellowish, especially on membrane between first and second spines; middle to distal part of membrane between second and third spines light blue. Second dorsal fin greyish translucent, with many orange markings forming four or five indefinite horizontal stripes. Two orange markings on center of caudal-fin base; dorsal one directed upward and ventral one directed downward. Remaining caudal fin greyish translucent, with many orange markings forming five to seven vertical bands. Anal fin greyish translucent proximally, orange distally, with a bluish-white margin. Pectoral fin translucent, but its proximal part cream yellow or yellowish-grey with orange markings aligned vertically along this cream yellow or yellowish-grey part both on proximal and distal sides. Pelvic disc translucent or grey without clear marking.

In female, markings and background color of body and fins similar to those of male, but markings reddish-brown or grey instead of orange and each marking smaller or less distinct. Diagonal stripe from above middle of upper lip usually broken in middle; posterior half of this marking forming part of series of markings horizontally aligned on cheek. First dorsal fin with no or faint black spot between first and second spines; yellowish and bluish color in distal part of fin indistinct. Pectoral fin with a pale-yellow spot on upper-proximal part. Pelvic disc translucent or light yellowish-grey.

Color in preservative ( Fig. 6a, b ): background of head and body cream and that of fins translucent or light grey. Orange, reddish-brown, and grey markings observed in life becoming brown. Pale orange or yellow patterns on opercular membrane, interopercle, and lower part of subopercle disappeared. All other yellow and bluish markings also disappeared.

Etymology. The new species is named Rhinogobius rong because its pointed appearance is reminiscent of the Vietnamese dragon (“rồng” in Vietnamese). The new specific name is a noun in apposition.

Comparison. The new species, Rhinogobius rong , is unique in that the anterior tip of the large (> 40 mm SL) male’s lower jaw protrudes significantly beyond upper jaw. In most other species, the anterior tips of lower and upper jaws are in approximately the same position, or the upper jaw protrudes more forward. Rhinogobius ngutinhoceps is the only other species known to have a lower jaw that protrudes beyond the upper jaw, but it has fewer pectoral-fin rays (16–17 vs. 18–20) and greater number of vertebrae (29 vs. 25–26) than the new species ( Endruweit 2018). The new species is also distinguished from other species by its distinctive markings, particularly the orange, reddish-brown, or grey markings on the head.

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 4. Rhinogobius rong immediately after fixation. a, NSMT-P 147886, holotype, male, 45.6 mm SL; b, OISTICH 255, paratype, female, 46.1 mm SL.

FIGURE 5. Live images of Rhinogobius rong in aquarium (a) and in situ underwater footage from Da Nang City, Vietnam (b–d). a, b, males, 12 January 2013; c, female, 12 January 2013; d, female, 1 March 2016 (photo by K. Maeda).

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.