Rhinogobius nammaensis, 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 : 90-91

Rhinogobius nammaensis , new species

(Figs. 2, 5, 8)

Material examined. – Holotype – ZRC 46582, 43.0 mm SL, Laos: Houaphan Prov., Nam Et upstream of Muang Et, Nam Ma basin, 20 o 48’25’’N 104 o 00’18’’E, coll. M. Kottelat et al., 8 May.1999.

Paratypes – ZRC 47675, 10 specimens, LARReC, uncat., 10 specimens, NMMBA uncat., 10 specimens , CMK 15370, 102 specimens, 20.3 – 40.8 mm SL, same data as holotype .

Diagnosis. – Rhinogobius nammaensis is distinguished from all other species of the genus by combination of the following characters: second dorsal fin rays modally I/8; anal fin rays I/7-8; pectoral fin rays modally 15; longitudinal scale series modally 32; vertebral count 11 + 17 = 28; first dorsal fin with rays III and IV longest; body with 6-7 lateral greyish to dark brown blotches; lateral side with 4-5 longitudinal rows of orange brown spots in male; cheek and opercle with 30-40 small, rounded brown spots and branchiostegal membrane with about 20 rounded light yellow spots in male. Description. – Body cylindrical anteriorly and compressed posteriorly. Body proportions in Table 1. Head moderately large, somewhat depressed in male. Eye large, dorsolateral. Snout in male slightly longer than in female. Bony interorbital narrow. Cheek fleshy in male. Lips thick. Mouth oblique, its rear edge extending to vertical through middle of orbit in male, merely reaching vertical through anterior margin of pupil in female. Both jaws with 3-4 rows of conical teeth, outer rows enlarged. Tongue tip rounded. Anterior nostril a short tube, posterior nostril a round hole. Gillopening wide, extending downward and slightly crossing the rear vertical of preopercle. Isthmus broad. 11 + 17 = 28 vertebrae (in 15 specimens).

Fins. D1 VI, D2 I/7-9 (mode 8); A I/7-8; P 15-18 (mode 16); V I/5 + I/5 (frequency distribution in Table 2). D1 rays III and IV longest, rear tip just reaching origin of D2 when depressed in male, not extending to origin of D 2 in female. D2 slightly higher than D1. D2 and A rear tips far away from C base when depressed. A origin inserted below vertical between 2nd and 3rd branched rays of D2. P oblong, rear tip extending to vertical of posterior end of D1, not reaching vertical of anus. V disc rounded, spinous rays with pointed membranous lobe. C elliptical, rear margin rounded.

Scales. Lateral trunk with moderately large ctenoid scales, anterior predorsal region naked; middle belly cycloid; scales in longitudinal series 30-32 (mode 32); transverse series 9- 11 (mode 10-11); predorsal median series 5-7 (mode 6); series between 1st dorsal and upper pectoral fin origin 6-7 (frequency distribution in Table 2). Head including opercle, prepectoral and prepelvic areas naked. Predorsal squamation with bifurcate anterior edge, anterior margin of predorsal middle squamation reaching vertical of pore, lateral squamation extending anteriorly beyond vertical through middle of posterior oculoscalupar canal.

Head lateral-line system. Canals. Nasal extension of anterior oculoscapular canal with terminal pores in front of posterior nostril. Anterior interorbital sections of oculoscapular canal separated, with paired pore. Pore present at posterior edge of eye. Posteriorbital section of anterior oculoscapular canal with pore, and terminal pore

but no pore; posterior oculoscapular canal present (with pores and), gap between two oculoscapular canals about half of 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 shorter than orbit. Rows c, d long, but not reaching to vertical of pore a. A single cp papilla. Row f paired. Opercular rows ot and oi slightly connected. Other details in Fig. 5 .

Colouration in alcohol. – Head and body yellowish brown or brown, body with 6-7 deep greyish to blackish brown blotches, more distinct and darker in female. Body with 4- 5 longitudinal rows of densely arranged brown spots in male, no such regularly-set rows of spots in female. Ventral side light yellow. Nape with irregularly deep or blackish brown marks. Dorsal side of snout with a V-shape dark brown stripe. Blotches sometimes irregularly marmorated or as a reticulated pattern in female. Cheek and opercle with 30-40 small, rounded brown spots in male, which size about half of pupil, and with several tiny irregular dark brown bars in female. Branchiostegal membrane greyish, in male with 15- 25 rounded light yellow spots (which might have been orange when fresh) and size modally about equal to pupil; membrane unmarked in female.

First dorsal fin grey with 2 black spots on middle of fin membrane before 3rd rays and basal half with 2 rows of dark spots in male; first dorsal fin yellowish with 3-4 rows of dark brown spots in female. Second dorsal fin with 4 longitudinal rows of dark brown spots and a narrow white edge. Anal fin grey and darker in distal half, with narrow white edge. Pectoral fin base with cluster of dark spots in upper part and a vertical row of spots at base in male, with a deep black spot in upper half in female. Caudal fin pale with 4-6 vertical rows of dark greyish brown spots. Pelvic fin pale and darker in basal part.

Distribution. – Rhinogobius nammaensis is presently known from the Nam Ma basin, in northeastern Laos, where it occurs in a variety of habitats from small forest streams to the main Nam Ma river, over stony substrate, in moderate current.

Etymology. – Named for the Nam Ma basin.

Remarks. – Rhinogobius nammaensis is very similar to R. mekongianus (Pellegrin & Fang) from the Mekong basin based on the similarly spotted cheek and similar fin-ray counts. However, it is distinguished from R. mekongianus by the following features: slightly higher counts of longitudinal scale rows (mode 32 vs. 29-30); length of row b shorter; smaller cheek spots in male; and lateral body lacking small rounded dark spots (except for the large blackish blotches) in female (vs. always with several longitudinal rows of dark spots).

Figures

Fig. 5. Rhinogobius nammaensis, ZRC 46582, 43.0 mm SL; head lateral-line system. Scale bar = 1 mm.