Crossocheilus elegans, Kottelat & Hui, 2011

Kottelat, Maurice & Hui, Tan Heok, 2011, Crossocheilus Elegans, A New Species Of Fish From Northern Borneo (Teleostei: Cyprinidae), Raffles Bulletin of Zoology 59 (2), pp. 195-199 : 195-198

Crossocheilus elegans , new species

( Fig. 1 )

Epalzeorhynchus kalliurus (non Smith, 1945): Inger & Chin, 1962: 99.

Crossocheilus cobitis (non Bleeker, 1853): Martin-Smith & Tan, 1998: 580.

Holotype. – ZRC 51184, 78.2 mm SL; Borneo: Sabah: Danum Valley, Kinabatangan drainage, stream at km 111 on main line west after turnoff to Borneo Rainforest Lodge (5°01'06.0"N 117°32'38.4"E); H. H. Tan et al., 3 Oct.1996.

Paratypes. – ZRC 40420, 1 , 85.4 mm SL; same data as holotype . – ZRC 44002, 3 , 35.3–106.3 mm SL; Borneo: Sabah: Danum Valley, Kinabatangan drainage, stream at km 113 on main line west (logging road) after turnoff to Borneo Rainforest Lodge (5°00'37.6"N 117°31'43.88"E); H. H. Tan et al., 3 Oct.1996 . – ZRC 40395, 3 , 74.1–96.8 mm SL; Borneo: Sabah: Danum Valley, Kinabatangan drainage, Sungai Malua at ca. km 95 on main line west after turnoff to Borneo Rainforest Lodge (5°05'43.5"N 117°37'33.2"E); H. H. Tan et al., 3 Oct.1996 . – CMK 20121 (ex-ZRC 43974), 3, 77.0– 83.6 mm SL; Borneo: Sabah: Danum Valley, Sungai Segama , in front of Danum Valley Field Centre (4°57'42.5"N 117°48'21.6"E); H. H. Tan et al., 1 Oct.1996 .

Diagnosis. – Crossocheilus elegans is immediately distinguished from all other species of the genus by its colour pattern consisting of a blackish midlateral stripe extending from the tip of the gill opening to the middle of the base of the caudal fin, separate from the dark brown dorsum by a pale yellowish brown stripe. In all other named Crossocheilus with a black midlateral stripe, the dorsum is olive brown, much paler than the midlateral stripe, and there is no yellow stripe between the dorsum and the black stripe.

Description. – General appearance in Fig. 1 ; morphometric data of holotype and 4 paratypes in Table 1. Dorsal fin with 3 simple and 8½ branched rays; origin above lateral line scale 9. Pectoral fin slightly falcate, with 14 rays, reaching ¾ of distance to pelvic-fin base. Pelvic fin triangular to slightly falcate, with 9 rays, reaching about 2 / 3 of distance to anal-fin origin and slightly beyond anus; axillary scale present. Anus separated from anal-fin origin by 3–4 scales. Anal with 2 simple and 5½ branched rays. Caudal fin with 10+9 principal rays, 9+8 branched. Caudal peduncle depth 1.49–1.65 times in length. 31–32 + 2–3 scales along lateral line, 8–10 predorsal scales, ½4/1/5½ scales in transverse line, ½3/1/3½ scales in transverse line on caudal peduncle, 3 or 3½ scales between lateral line and pelvic-fin origin.

Rostral barbel about equal to eye diameter, maxillary barbel about 2 / 3 of eye diameter. Upper lip with 12–17 fimbriae, entirely covered by small papillae. Anterior edge of lower lip with a few large papillae.

Coloration. – Upper surface of head grayish brown, lower surface yellow. Body background pale yellowish brown. A conspicuous blackish brown midlateral stripe about 2 scales wide, from upper extremity of gill opening to base of caudal fin, extending onto proximal-most part of median caudal-fin rays. Midlateral stripe margined above by a pale yellowish-brown stripe about 1 to 1.5 scale wide, sometimes continued on head by a pale area behind eye. Dorsum dark brown, with darker scale margins and scale pockets forming a reticulate pattern, sometimes forming a narrow darker line along yellowish stripe below. Scales on rows 1–2 under midlateral stripe with dark brown pockets, sometimes forming a reticulate pattern. Fins hyaline. Distal half of anterior pectoral rays dark brown. In largest specimens, caudal fin with dark brown membranes between outermost principal rays of each lobe.

Distribution. – Crossocheilus elegans is currently known from Sabah where it has been caught only in Segama and Kinabatangan drainages.

Habitat. – Crossocheilus elegans occurs in hill-stream habitats, usually near or in the riffle zone in fast flowing waters over a rocky bottom. At different sites, the following species have been found associated with C. elegans : Anguilla borneensis (Anguillidae) , Garra borneensis , Hampala sabana , Lobocheilos unicornis , L. erinaceus , Paracrossochilus acerus , Schismatorhynchos holorhynchos , Tor tambra , T. tambroides (Cyprinidae) , Gastromyzon aequabilis , G. danumensis , G. lepidogaster , G. ornaticauda , G. pariclavis , G. spectabilis , Homaloptera stephensoni , Neogastromyzon crassiobex , Parhomaloptera microstoma (Balitoridae) , Glyptothorax major (Sisoridae) , and Macrognathus keithi (Mastacembelidae) . See Martin-Smith & Tan (1998) and Tan (2006) for details.

Etymology. – From the Latin elegans, meaning elegant. An adjective.

Remarks. – Crossocheilus elegans has first been recorded by Inger & Chin (1962: 99) who identified it as Epalzeorhynchos kalliurus Smith, 1945 . Their material had also been collected in the same drainage as C. elegans (Kinabatangan) and shares the unique (within Crossocheilus ) colour pattern of C. elegans , the blackish midlateral stripe extending from the tip of the gill opening to the middle of the base of the caudal fin, separate from the dark brown dorsum by a pale yellowish brown stripe. Nothing in Inger & Chin’s description suggests that their material could belong to a species other than C. elegans .

Crossocheilus elegans is not a member of the genus Epalzeorhynchos . The genus Epalzeorhynchos is diagnosed by the presence of a rostral lobe, a character shared with no other genus. The rostral lobe is an elongate conical structure, with a conspicuous conical tubercle at its tip and a series of conical and starry tubercles along its lower edge. It is encased in a widened sublachrymal groove (which borders the rostral fold) and surrounds the rostral barbel. The lobe is movable, and can rotate upwards along a more or less longitudinal axis to reach a position above the sublachrymal groove (Zhang & Kottelat, 2006; Yang & Winterbottom, 1998). This structure is not present in C. elegans .

Epalzeorhynchos kalliurus was originally described from the Mekong in northern Thailand on the basis of a single specimen ( Smith, 1945: 264). Epalzeorhynchos kalliurus does not have the rostral lobe that diagnoses the genus Epalzeorhynchos (see above). Banarescu (1986: 149) considered E. kalliurus as a synonym of C. cobitis ( Bleeker, 1853) , but he noted (p. 150) that the holotype had been examined by R. M. Bailey who identified it as C. reticulatus . On the contrary, Rainboth (1996: 119) considered C. calliurus as probably distinct from C. cobitis , based on the lateral line scale count and a different colour pattern. (Rainboth did not give additional details on material and localities since his work is an identification guide and the format did not allow to list examined material or discussion). The colour pattern of C. kalliurus sensu Rainboth is made of a diffuse lateral stripe on posterior half of body, a diffuse blotch on the caudal peduncle and a sharply defined spot at the base of the caudal-fin rays. His figure was Smith’s (1945) figure of the holotype in the original description. Whether or not C. kalliurus is distinct from C. cobitis or C. reticulatus , the unique colour pattern of C. elegans (see diagnosis) distinguishes it at once from all. Crossocheilus reticulatus is endemic to the Mekong and Chao Phraya drainages in Thailand, Cambodia and Laos; it has a large black blotch on the caudal peduncle, a reticulate pattern on the flank and the dorsum, made of the black margin of scales, and no midlateral black stripe.

Banarescu (1986) examined Inger & Chin’s (1962) material and concluded that they are C. cobitis , based on the presence of two pairs of barbels and on the lateral line scale count. Tan & Kottelat (2009: 32) reviewed the species of Cobitis of Sumatra and discussed the identity of C. cobitis . Crossocheilus cobitis is the most common species of the genus. It is a small species (up to 52 mm SL, mature at about 40–45 mm SL) commonly found in the lowlands, in murky waters, usually with muddy bottom, under logs, floating houses, boats, etc. It has two pairs of barbels; a continuous midlateral stripe from the tip of the snout to the base of the caudal fin, with a conspicuous small blotch at the posterior extremity, faintly marked on the caudal fin; a faint mark between the anus and the anal-fin origin in juveniles; and a narrow mouth.

Several species had been confused under the name C. cobitis , all with a similar habitat in lowland murky waters (Tan & Kottelat, 2009: 32). Lim & Wong (1994: 44) in their inventory of fishes from the Kinabatangan basin recorded a ‘ C. cobitis ’ from the lower part of the drainage in turbid water and with habits similar to that described above for C. cobitis . The identity of this species cannot be cleared without addressing also that of the other C. cobitis -like species on Borneo, which is beyond the scope of the present study [it can be noted, however, that when compared to populations from southern Borneo (e.g. Kapuas), the Kinabatangan species has a shorter snout, the dorsal-fin origin conspicuously more forward, a slender caudal peduncle and a narrower mouth]. Crossocheilus elegans is known from the upper part of the Kinabatangan drainage, in hill-stream habitats, with fast and clear water. It is distinguished from C. cobitis (and the other similar species) in having the midlateral stripe starting at the upper extremity of the gill opening (vs. at the tip of the snout), a conspicuous and contrasted yellowish stripe between the blackish brown midlateral stripe and the dark brown dorsum (vs. a paler stripe may be present but never so contrasted and the dorsum is paler brown) and often margined above by a narrow line formed by a row of darker scale pockets (vs. no such line), scales on rows 1–2 under midlateral stripe and on dorsum with dark brown pockets, sometimes forming a reticulate pattern (vs. no conspicuous reticulate pattern), and midlateral stripe not ending in a conspicuous small black blotch at the base of the caudal fin (vs. blotch present).

Figures

Fig. 1. Crossocheilus elegans, holotype, ZRC 51184, 78.2 mm SL (dorsal, lateral and ventral views); Sabah: Danum Valley, Kinabatangan drainage.