Draconectes narinosus, Kottelat & Ch-, 2012

Kottelat, Maurice, 2012, Draconectes narinosus, a new genus and species of cave fish from an island of Halong Bay, Vietnam (Teleostei: Nemacheilidae), Revue suisse de Zoologie 119 (3), pp. 341-349 : 342-347

Draconectes narinosus new species

Figs 1-3

HOLOTYPE: MHNG 2730.080 , 24.7 mm SL; Vietnam: Quang Ninh Province: Ha Long Bay: island Dáo Van Giò : phreatic lake in cave Dông Duc Tiên, 20°50.34'N 107°16.77'E; B. Sket, 17 June 2003.

PARATYPE: OBBFUL uncat., 20.8 mm SL; same data as holotype.

DIAGNOSIS: Draconectes­narinosus is the only known species of the genus; see diagnosis of genus.

DESCRIPTION: See Figure 1 for general appearance and Table 1 for morphometric data of holotype and paratype. The specimens are quite soft and uneasy to handle, and consequently the description of the soft anatomy uneasy and sometimes approximate. A moderately elongate nemacheilid with body depth about equal from head to dorsal-fin origin. Behind dorsal fin, body depth decreasing to caudal-fin base. Head slightly depressed, anterior half conspicuously depressed. Body rounded anteriorly to compressed posteriorly. Genital papilla very large (compared to other species of nemacheilids). Conspicuous dorsal and ventral crests on caudal peduncle, starting very close to posterior extremity of dorsal- and anal-fin bases, outline of dorsal crest continuous with dorsal outline of caudal fin. Caudal peduncle 1.7-2.0 times longer than deep (depth including crest). Largest recorded size 24.7 mm SL.

Dorsal fin with 4 simple and 7 branched rays (a single ray articulating on last pterygiophore); distal margin straight. Pectoral fin with 11 rays, reaching about halfway to 3/5 of distance to pelvic-fin base. No pelvic axillary lobe. Pelvic fin with 6 rays, reaching about ¾ of distance to anal-fin origin, not reaching anus which is situated immediately in front of anal fin; origin slightly in front of vertical through dorsal-fin origin. Anal fin with 3 simple and 5 branched rays (a single ray articulating on last pterygiophore). Caudal fin forked, with 7+6 branched rays, with very narrow interradial membranes resulting in an elongated appearance; procurrent rays difficult to count, at least 8 dorsal and 7 ventral.

No scales on body. Lateral line indistinct but complete, marked by a series of 30-40 papillae along its course, apparently each with a pore at its tip. Four and six similar papillae on each side of dorsal-fin base of holotype, possibly with a pore; apparently 2 papillae in paratype. Pores of cephalic lateral line system also situated at tip of papillae ( Fig. 2 ), difficult to count with accuracy because of state of fixation and because of presence of other, unpored papillae. 9 (?) supraorbital, 13 (?) preoperculomandibular (large, organised in a regular canal until angle of mouth) and 3 (?) hardly distinct supratemporal pores. Infraorbital row present, difficult to distinguish, about 9-12 (?) papillae/pores along anterior part of canal. Supraorbital canals almost meeting anteriorly.

Nostrils adjacent, posterior opening larger than anterior one; anterior nostril at tip of a short and broad tube; olfactory rosette slightly protruding through posterior opening. Mouth gape about 2 times wider than long ( Fig. 1 ). Lips thin but fleshy, apparently smooth. No median incision in upper lip. A median notch in lower lip, shallow but long. No processus dentiformis. A median concavity in lower jaw. Inner rostral barbel reaching about to corner of mouth; outer one reaching about ½ of lateral head length. Maxillary barbel reaching about 2/3 of lateral head length. Shape of intestine unknown (specimens not dissected).

SEXUAL DIMORPHISM: No external character observed that would be indicative of sexual dimorphism.

COLORATION: When preserved, body background pale yellowish. Dark brown pigments on upper half of flank, giving a pale brownish appearance, denser along midlateral axis and on back in front of dorsal fin. Papillae of lateral line and along base of dorsal fin with dark brown pigments. Head pale yellowish, darker along posterior edge of skull, around rim of posterior nostril and at possible position of a foramen. Difference between brownish dorsal and white ventral parts of head very contrasted. Dorsal crest and posterior half of ventral crest brownish. Two darker brown patches at base of caudal-fin rays. Fins hyaline.

In life (based on photographs, Fig. 3 ): Body pale reddish brown. A faint roundish greyish mark at end of caudal peduncle. Papillae along base of dorsal fin blackish.

DISTRIBUTION: Presently known only from the type locality, in Dong Duc Tien cave, on Dao Van Gio island, in Halong Bay. Dao Van Gio is located in the eastern part of Ha Long Bay, about 15 km off the coast.

NOTES ON BIOLOGY: The following information are provided by the collector, Boris Sket (in litt, 31 Oct. 2004). The only water body of a phreatic (not anchihaline) character that could be reached on a small island of Ha Long Bay was inside Dong Duc Tien cave on Dao Van Gio island, a very dissected karst island. Altitude was not measured but is estimated to have been at about sea level. At the time of the visit it was a 'lake' approximately 100 x 20 m, fragmented by large boulders into a system of interconnected basins with loamy bottom and up to 1.5 m deep. The water was totally stagnant. As can be inferred from its fauna, this body of water is, at least during highest water levels, connected and included into a general phreatic water body of the island. Its water is nearly limnic (4-5 ppt salinity). The island is slightly over 1 km 2 and extremely ramified, the width of the branches reaching a maximum of 400 m, and only at a few locations.

Five fish individuals have been sighted, but only two of them caught. Another interesting and exceptional animal from this lake is the moderately dense population of a tiny troglomorphic amphipod of the family Sebidae (Seborgia­ vietnamica Jaume, Sket & Boxshall, 2009); it most probably serves as the main food supply for the fish. Copepods and oligochaetes were extremely scarce.

ETYMOLOGY: The Latin narinosus means 'who has large nostrils'. An adjective.

REMARKS: It is not possible to determine the relationships of D.­ narinosus and it is not possible to place it in any of the recognised genera, and therefore it is placed in a new genus. Some of the characters used to diagnose the genus (absence of eye and scales, pale body) are obviously related with the cave habitat and as such reductive and not informative about relationships. The pores of the cephalic and body lateral line system situated at the tip of papillae is apparently unique in nemacheilids; this character too is possibly an adaptation to cave habitat. The relatively large nostrils and their wide openings are apparently unique in the family, as are the papillae along the base of the dorsal fin.

Schistura­papulifera Kottelat et­al., 2007, a cave species from Assam, India, also has projections on the head, but in this species the head is covered by small skin projections, the pores of the cephalic lateral line system are not situated at the tip of papillae and there are 5 pores in the supratemporal canal (vs. 3 in Draconectes ).

Most Southeast Asian species of nemacheilids have 9+8 branched caudal-fin rays. This number is sometimes reduced by 1 or 2 in some species (8+8, 8+7); in such cases it is usually a reliable diagnostic character (e.g. Kottelat, 1990a, 2000). The reduced number of caudal-fin rays is usually associated with small size in nemacheilids (e.g., Schistura­paucicincta Kottelat, 1990a, S.­rikiki­ Kottelat, 2000, S.­ diminuta Ou et al., 2011 ) and other fishes (e.g. Paedocypris, see Kottelat et­al., 2006, Britz & Conway, 2011), but small size is not always associated with reduced number of caudal rays (e.g. Sundadanio, see Conway et­al., 2011).

Many genera and species of East Asian nemacheilids have a lower number of branched caudal-fin rays. The reduced number of caudal-fin rays (13) in Draconectes , is shared with the genera Oreonectes (12-16; Du et­ al., 2008) and Lefua (13-15; Sawada, 1982). Draconectes is distinguished from Lefua and Oreonectes in having the anterior and posterior nostrils adjacent (vs. widely separated, posterior one at short distance of anterior margin of orbit); the anterior nostril situated at the tip of a short and wide tube (vs. on a short and narrow tube whose posterior rim is produced in a long filament, the 'nasal barbel'); a complete lateral line (vs. absent or up to 18 pores, not reaching vertical of pelvic fin); and the dorsal-fin origin slightly behind a vertical through pelvic-fin origin (vs. conspicuously behind the base of the pelvic fin in some Oreonectes ). Oreonectes occurs in southeastern China and northern Vietnam; and Lefua in the Amur drainage, Korea, northeastern China and Japan.

As presently understood, Oreonectes includes eleven valid species (Kottelat, in press), several of them known from cave habitats. They can be separated into two groups. The first group includes five species (O.­ anophthalmus Zheng, 1981 , O.­ guananensis Yang et­ al., 2011a, O.­ luochengensis Yang et­ al., 2011b, O.­ platycephalus Günther, 1868 , O.­ polystigmus Du et­al., 2008) that have, among other characters, a rounded caudal fin and the dorsal-fin origin clearly behind the pelvic-fin origin; this group includes O.­ platycephalus , the type species of the genus. This first group is present in Guangxi and Guangdong provinces in China and in coastal streams of Vietnam (northeast of Halong; Kottelat, 2001). According to Tang et­al. (2012), all but O.­ platycephalus are known from caves. Du et­ al. (2008) and Huang et­ al. (2009) considered that a sixth species, O.­ retrodorsalis Lan et­al., 1996, also belongs to this first group, in which it is the only species with an emarginate caudal fin; the figure in the original description ( Lan, Yang & Chen, 1996) shows a forked caudal fin with rounded lobes.

The second group includes species that have, among other characters, a forked caudal fin, the dorsal-fin origin in front of the pelvic-fin origin, a more slender body and a distinct dorsal crest on the caudal peduncle. This second group includes five named species (O.­ elongatus Tang et­al., 2012, O.­ furcocaudalis Zhu & Cao, 1987 , O. macrolepis Huang et­ al., 2009, O.­ microphthalmus Du et­ al., 2008, O.­ translucens Zhang et­ al., 2006), all known only from Guangxi, China. All have been collected inside caves (Tang et­al., 2012). These species do not seem congeneric with O.­ platycephalus , but in the absence of material I cannot comment on their status. It is further not clear whether all species in this second group are closely related; the illustration in the original description of O.­ macrolepis (Huang et­al., 2009) shows a fish with a more rounded body (vs. compressed in the other species), rounded head (vs. pointed) and rounded caudal-fin lobes (vs. pointed). Draconectes potentially could have relationships with some of them but is distinguished from all by the adjacent anterior and posterior nostrils.

The nemacheilid fauna of northern Vietnam and coastal drainages of Guangxi is still poorly known (Kottelat, 2001, pers. obs.; Freyhof & Serov., 2001); the recent poor descriptions of several species ( Nguyen, 2005) has compounded the situation. The species reported from adjacent areas of the mainland include Oreonectes­platycephalus, Traccatichthys­taeniatus and various species of Schistura ( Kottelat, 2001a) . The epigean relatives of Draconectes probably await discovery. It is remarkable that the species managed to survive on such a small island and at such low altitude within a maze of sunken karst landscape.

Figures

FIG. 1 Draconectes­narinosus, MHNG 2730.080, 24.7 mm SL; Vietnam: Ha Long Bay: Dao Van Gio island, Dong Duc Tien cave; right side, reversed. Photographs by Tan Heok Hui.

FIG. 2 Draconectes­narinosus, OBBFUL, uncat., 20.8 mm SL; dorsal view of head. an, anterior nostril; ip, pores of infraorbital row; pn, posterior nostril; sp, pore of supraorbital row. Photograph by Boris Sket.

FIG. 3 Draconectes­narinosus, MHNG 2730.080, 24.7 mm SL; Vietnam: Ha Long Bay: Dao Van Gio island, Dong Duc Tien cave; immediately after capture. Photograph by Boris Sket.