Rhinogobius boa, Chen & Kottelat, 2005

Chen, I-Shiung & Kottelat, Maurice, 2005, Four new freshwater gobies of the genus Rhinogobius (Teleostei: Gobiidae) from northern Vietnam, Journal of Natural History 39 (17), pp. 1407-1429 : 1409-1413

Rhinogobius boa new species

( Figures 2 , 6 , 10 )

Material examined

Holotype: ZRC 49206, 27.7 mm SL, Vietnam: Quang Ninh Province, Hai Ninh District , torrent at km 5 on road Bac Phong Sinh to Mong Cai, 21 ° 359310N, 107 ° 439520E, coll. M. Kottelat et al., 2 October 1998 . Paratypes: CMK 14896, five specimens , ZRC 49207, four specimens, 26.9–33.9 mm SL, other data same as above . CMK 14890, four specimens, 22.2–32.9 mm SL, Vietnam: Quang Ninh Province, Hai Ninh District , forest creek at km 3 on road from Bac Phong Sinh to Mong Cai, 21 ° 369430N, 107 ° 439549E, coll. M. Kottelat et al., 2 October 1998 .

Diagnosis

Rhingobius boa is distinguished from all congeners by the unique combination of the following features: cheek with two small greyish brown spots on lower margin; branchiostegal membrane grey with 8–10 dark grey marks in male; first dorsal fin with a broad median brown black mark in front of fourth spinous ray in male, none in female; pectoral fin base usually with two round brown spots in both sexes; caudal fin base with a median chevron-shaped black spot; body with six to seven deep brown blotches; scale pockets with brown or deep brown margin; second dorsal fin rays eight; anal fin rays six to seven; pectoral fin rays 16; longitudinal scale rows 30–31; predorsal median series 10–12; and vertebrae 27.

Description. Body slender, cylindrical anteriorly, compressed posteriorly. Body proportions in Table I. Head moderately large, slightly depressed anteriorly. Eye large, lips thick. Mouth oblique, rear edge reaching vertical through anterior margin of pupil in both sexes. Both jaws with three to four rows of conical teeth, outer rows enlarged. Tongue margin rounded. Anterior nostril a short tube and posterior one a round hole. Gill opening extending to vertical through rear margin of preopercle. Isthmus broad. 10+17527 vertebrae.

Fins. D1 VI; D2 I/8; A I/6–7; P 16; V I/5+I/5 (frequency distribution in Table II). D1 rays II, III longest, rear tip extending to origin of D 2 in male but not reaching this point in female. A origin inserted below second branched ray of D2. P large, its rear margin extending beyond vertical of anus in male, not extending to that point in female. V disc rounded, spinous rays with pointed membranous lobe. C rounded, rear edge rounded.

Scales. Body with moderately large ctenoid scales, anterior part of predorsal area naked; scales on posterior predorsal region and belly cycloid; scales in longitudinal series 30–33 (mode 31); transverse series eight; predorsal median series 11–12; series between 1st dorsal and upper pectoral fin origin six to seven (mode seven) (frequency distribution in Table III). Head including opercle, preopercle and prepelvic areas naked. Predorsal squamation with slightly trifurcate anterior edge, anterior extension of median series reaching the midline of gap between anterior and posterior oculoscapular canals.

Head lateral-line system. Canals: nasal extension of anterior oculoscapular canal with terminal pores S above and near posterior nostrils. Anterior interorbital section of oculoscapular canal separated, with paired pores l. A single pore K in posterior interorbital region. Pore v present at posterior edge of eye. Gap between anterior and posterior oculoscapular canals about equal to length of posterior oculoscapular canal. Preopercular canal with three pores c, d, E.

Sensory papillae: row a not reaching midline of orbit. Length of row b about half of orbit. Row c, d long, not reaching vertical of pore a. A single cp papilla. Row f paired. Opercular rows ot and oi well separated.

Coloration in alcohol. Head and body yellowish brown. Body with six to seven deep brown blotches. Scale pockets with brown or deep brown margin. Dorsal side of snout with a pair of brown lines united at tip of snout. A dark blotch just below orbit. A longitudinal brown stripe behind orbit. Cheek with a median greyish stripe in both sexes. Cheek with two greyish brown spots along lower margin. Branchiostegal membrane uniformly light in both sexes, with 8–10 dark grey marks in male.

First dorsal fin with light margin and a broad median brown black mark in front of fourth spinous ray in male, none in female. Second dorsal fin with two basal rows of blackish brown spots and greyish distal region in male, uniformly whitish with three rows of longitudinal brown spots in female. Anal fin greyish with light margin. Pectoral fin whitish, fin base usually with two round brown spots in both sexes. Caudal fin with three to four vertical rows of greyish lines or spots, fin base with a median chevron-shaped black spot. Pelvic fin pale greyish brown in male, white in female.

Distribution

Rhinogobius boa is presently known only from small streams of the Ka Longo drainage and adjacent coastal streams. Ka Longo makes the border between Vietnam and China and is known as Beilun He in China. The habitats were a small stream in foothills, under forest cover, and a steep torrent with a succession of large boulders, falls, and shallow pools covered by leaf litter.

Etymology

From the latin boa (measles, red spots disease), derived from boarius, bovarius (bovines), because Romans used cow-dung to cure measles. An allusion to the red spots on the cheeks and branchiostegal membrane. A noun in apposition.

Remarks

Rhinogobius boa is more similar to R. wangchuangensis Chen et al., 2002 (a species endemic to Hainan) than to any other species of southern China. However, they can be distinguished by the following combinations of features: (1) predrosal squamation: more anterior extension of predorsal scales on middle series in R. boa than R. wangchuangensis (11–12 versus three to six) and (2) coloration pattern: pectoral fin base always with two round brown spots in R. boa versus a single one in R. wangchuangensis ; and most of body scale pockets with brown or deep brown margin in R. boa versus all body scale pockets unmarked in R. wangchuangensis .

During the lower sea level resulting from glaciations, the Song Hong and part of the Hainan rivers formed a single drainage across the exposed floor of the present Gulf of Tonkin, explaining the fact that a number of species are endemic to an entity consisting of the lower Song Hong, Hainan and small coastal streams between, in northern Vietnam and Guangxi Province of China, and that pairs of closely related species inhabit Hainan, on the one hand, and the Red River basin, on the other hand.

Figures

Figure 2. Head lateral-line system of Rhinogobius boa, paratype, CMK 14986, 26.7 mm SL. Scale bar: 1 mm.

Figure 6. Rhinogobius boa, holotype, ZRC 49206, 27.7 mm SL, cephalic colour pattern of male. Scale bar: 1 mm.

Figure 10. Rhinogobius boa. (A) Male, holotype, ZRC 49206, 27.7 mm SL; (B) female, paratype, ZRC 49207, 33.9 mm SL.