Rhinogobius milleri, Chen & Kottelat, 2003

Chen, I-Shiung & Kottelat, Maurice, 2003, Three New Freshwater Gobies Of The Genus Rhinogobius (Teleostei: Gobiidae) From Northeastern Laos, Raffles Bulletin of Zoology 51 (1), pp. 87-95 : 88-90

Rhinogobius milleri , new species

( Figs. 1 , 4 , 7 )

Material examined. – Holotype – ZRC 46581, 39.8 mm SL, Laos: Xiangkhouang Prov., Nam Kuang (a tributary of Nam Mat), about 2 km SW of Ban Lao, 19 o 38’35’’N 103 o 28’52’’E, coll. M. Kottelat et al., 2 May.1999.

Paratypes – ZRC 47674, 4 specimens, LARReC uncat., 4 specimens , CMK 15249, 12 specimens, 14.1 – 45.8 mm SL, data same as holotype. NMMBA uncat., 4 specimens , CMK 15256, 16 specimens, 22.0 – 33.8 mm SL, Laos: Xiangkhouang Prov., Nam Tian, about 2 km upstream of its confluence with Nam Mat , 19 o 34’40’’N 103 o 41’12’’E, coll. M. Kottelat et al., 2 May.1999 . CMK 15272, 5 specimens, 27.3 – 45.7 mm SL, Laos: Xiangkhouang Prov., Nam Ken, a small creek making the border with Vietnam at Ban Xayden , 19 o 28’19’’N 104 o 5’4’’E, coll. M. Kottelat et al., 3 May.1999 . CMK 15283, 24 specimens, 12.9 – 30.1 mm SL, Laos: Xiangkhouang Prov., Nam Mat about 1 km East of Ban Phathang, 19 o 36’33’’N 103 o 42’10’’E, coll. M. Kottelat et al., 4 May.1999 .

Diagnosis. – Rhinogobius milleri can be distinguished from all other species of the genus by the unique combination of

the following characters: second dorsal fin rays modally I/ 8; anal fin rays I/7; pectoral fin rays modally 16; longitudinal scale series 28-31; predorsal scales 6-10; vertebral counts 10+ 17 = 27; first dorsal fin with rays IV and V longest; body with 8 somewhat squarish dark brown blotches and wider than interspaces; lower edge of cheek with three brownish black spots and branchiostegal membrane with 35 - 50 small, rounded white spots in male; and caudal fin base with vertical black bar.

Description. – Body cylindrical anteriorly and compressed posteriorly. Body proportions in Table 1. Head moderately large; quite depressed in male. Eye large, dorsolateral. Snout pointed. Cheek very fleshy. Lips thick. Mouth oblique, rear edge reaching vertical through middle of orbit. Both jaws with 3-4 rows of conical teeth, and outer rows enlarged. Tongue margin rounded. Anterior nostril a short tube and posterior one a round hole. Gill-opening extending near edge of preopercle. Isthmus broad. 10 + 17 = 27 vertebrae.

Fins. D1 VI; D2 I/8; A I/7; P 15-16 (mode 16); V I/5 + I/ 5 (frequency distribution in Table 2). D1 IV and V spinous rays longest, with rear tip extending to base of 2nd branched rays of D 2 in male, not extending to origin of D 2 in female. Origin of A inserted below origin of 3rd branched ray of D2. P large and oblong, its rear margin extending to vertical through anus in male, never reaching this vertical in female. V disc rounded, spinous rays with pointed membranous lobe. C elliptical, rear edge rounded.

Scales. Body with moderately large ctenoid scales, anterior predorsal area naked; posterior predorsal region and belly cycloid; scales in longitudinal series 28-31 (mode 29); transverse series 8-10 (mode 9); predorsal median series 8- 10 (mode 8-9); series between 1st dorsal and upper pectoral fin origin 6-8 (mode 7) (frequency distribution in Table 2). Head including opercle, preopercle, and prepelvic areas

naked. Predorsal squamation with trifurcate anterior edge, anterior tip of predorsal middle squamation reaching about vertical of middle region of posterior oculoscapular canal, lateral squamation extending to gap between two oculoscapular canals.

Head lateral-line system. Canals. Nasal extension of anterior oculoscapular canal with terminal pores slightly in front of posterior nostril. Anterior interorbital sections of oculoscapular canal separated, with paired pores. A single pore k in posterior interorbital region. Pore present at posteriodorsal edge of eye. Gap between anterior and posterior oculoscapular canals smaller than length of posterior oculoscapular canal. Preopercular canal present with pores r, and. Sensory papillae. Row a extending to vertical through middle of orbit. Length of row b about equal to orbit. Rows c, d long, but not reaching vertical of pore. A single cp papilla. Row f paired. Opercular rows ot and oi slightly connected. Other details in Fig.4 .

Colouration in alcohol. – Head and body yellowish brown in female and brown in male. Body always with 8 somewhat square blackish brown blotches. Blotches wider than interspaces. Four discontinuous, longitudinal dark brown lines on lateral side. Belly yellowish to light grey. Nape with dark brown bars and stripes. C base with a conspicuous short, black bar. Dorsal side of snout with a pair of blackish brown lines united at tip of snout. A square greyish brown mark below eye. A longitudinal brown line on middle of cheek. Lower part of cheek with irregular tiny brown dots, and lower edge of cheek with three rounded, brownish black spots in male. Branchiostegal membrane grey with 35 - 50 denselyset, small, rounded white spots (reddish orange or red in life) in male; membrane uniform dark grey and unmarked in female.

First dorsal fin grey with light margin and black marks in front of 3rd spinous ray in male, yellowish with 2-3 rows of brown spots in female. Second dorsal fin grey with 2-3 longitudinal rows of brownish black spots in male, yellowish white with 3-4 longitudinal rows of dark brown spots in female. Pectoral fin grey with radiating black lines on membrane, a black spot slightly above middle region of base, and usually another black spot on lower basal part in adult male. Pectoral fin yellowish with a black spot above middle of base in female. A semicircular yellowish grey region near pectoral fin base in both sexes. Membrane of anal fin grey to dark grey with narrow white margin. Caudal fin pale or yellowish with 3-5 vertical rows of dark brown spots in male and in some larger males with many radiating greyish brown lines on membranes; and with 5-6 rows of blackish brown spots in female. Pelvic fin dark grey in male and yellowish in female.

Distribution. – Rhinogobius milleri has only been found in small forest creeks of the Nam Mat and Nam Mo basins in Laos. Its distribution range is expected to extend into Vietnam and possibly to other basins draining to the Gulf of Tonkin.

Etymology. – The new species is named for Prof. Peter J. Miller in appreciation for his very kind support to the studies and researches of the first author.

Remarks. – Among the species recorded from the adjacent river basins, R. milleri seems to be most similar to R. taenigena Chen, Kottelat & Miller, 1999 , based on similar scale counts and coloration pattern of cheek consisting of a greyish longitudinal stripe. However, it can be distinguished from R. taenigena by the following combination of characters: fewer anal fin rays (I/7 vs. I/8); lower margin of cheek always with 3 black spots in male (vs. 4); and branchiostegal membrane with more round spots in male (35- 50 vs. 23-25).

Figures

Fig. 1. Rhinogobius milleri, CMK 15249, paratypes, (a) male, 39.2 mm SL, and (b) female, 45.8 mm SL; Laos: Nam Kuang.

Fig. 4. Rhinogobius milleri, holotype, ZRC 46581, 39.8 mm SL; head lateral-line system. Scale bar = 1 mm.

Fig. 7. Rhinogobius milleri, holotype, ZRC 46581, 39.8 mm SL; cephalic colour pattern of male. Scale bar = 1 mm.