Acanthocobitis pictilis, Kottelat, Maurice, 2012

Kottelat, Maurice, 2012, Acanthocobitis pictilis, a new species of loach from Myanmar and Thailand (Teleostei: Nemacheilidae), Zootaxa 3327, pp. 45-52 : 45-51

Acanthocobitis pictilis , new species

( Fig. 1 )

Acanthocobitis botia (non Hamilton, 1822): Kottelat 1990: 29 (in part; Mae Khlong)

Holotype. MHNG 2727.066 , 71.8 mm SL; Myanmar: Kayin State: stream 'Chon Son' between Kyondaw and Phadaw , about 20 km northwest of Payathouzu (at border with Thailand near Chedi Sam Ong, Three Pagoda Pass); approx 15°25'N 98°15'E; K. Kubota, December 2002.

Paratypes. CMK 17509, 5, 65.4–80.0 mm SL; Myanmar: Zami drainage near Kyandaw, approx. 15°18'N 98°18'E [Kyandaw is about 20 km northwest of Chedi Sam Ong (Three Pagoda Pass)]; K. Kubota, June 2002. — MHNG 2727.067, 2; ZRC 53376, 1; CMK 17777, 5; 55.6–63.1 mm SL; same data as holotype. — CMK 17967, 2, 64.1–64.3 mm SL; same locality as holotype; K. Kubota, 1 June 2003. — ZRC 53377, 1, 77.1 mm SL; CMK 18429, 1, 91.5 mm SL; same locality as holotype; M. Kottelat & K. Kubota, 1 May 2004. — CMK 14601, 1, 69.6 mm SL; Thailand: Kanchanaburi Prov.: Mae Nam Khwae Noi basin: Nam Khung near Ban Huai Pak Khung; 14°39'35"N 98°32'02"E; M. Kottelat & K. Kubota, 4 April 1998. — CMK 17249, 2, 63.0–69.8 mm SL; same locality; M. Kottelat et al., 29 March 2002 .

Diagnosis. Acanthocobitis pictilis is distinguished from all other species of the genus by its colour pattern, especially the dark brown triangular saddles in the upper half of the body, strongly slanted anteriorly and becoming almost vertical posteriorly. In larger specimens, the median part of the saddles become paler and it may appear as a pair of dark brown lines. Other characters useful to distinguish the species, but not unique to it are: lateral line complete; 12½ or 13½ branched dorsal-fin rays; 8+8 or 7+8 branched caudal fin rays; males with deep slit on the cheek ( Fig. 2 a), extending from lower margin of eye to above base of posterior rostral barbel; 6–8 vertical lines or rows of spots on caudal fin; and 6–7 longitudinal lines or rows of spots on dorsal fin.

Description. See Figure 1 for general appearance and Table 1 for morphometric data of holotype and 16 paratypes. A moderately elongate nemacheilid (sensu Šlechtová et al., 2007) with body depth increasing until slightly in front of dorsal-fin origin. Behind dorsal fin, body depth decreasing slowly to caudal-fin base. Head slightly compressed; body compressed. Largest recorded size 91.5 mm SL.

Dorsal fin with 4 simple and 12½ (10) or 13½ (7) branched rays; distal margin slightly concave. Pectoral fin with 1 simple and 12 (9), 13 (6) or 14 (1) branched rays; reaching about 2/3 of distance to pelvic-fin base; tip of rays projecting slightly beyond membranes. Axillary pelvic lobe present. Pelvic fin with 1 simple and 6 (1) or 7 (16) branched rays, reaching about ½ to 3/5 of distance to anal-fin origin, not reaching anus, which is situated about one eye diameter in front of anal fin; origin under base of branched dorsal-fin rays 3 to 4. Anal fin with 3 simple and 5½ branched rays. Caudal fin slightly emarginate, with 7+8 (3) or 8+8 (11) branched rays. Low ventral and dorsal crests on posterior half of caudal peduncle, which is 1.0–1.3 times longer than deep.

Body entirely covered by scales, except around 4–5 first lateral line pores; scales embedded on belly. Lateral line complete, with 80–90 pores (most specimens 87–88). Cephalic lateral line system with 6 supraorbital, 4 + 10–12 infraorbital, 10 preoperculo-mandibular and 3 supratemporal pores (5 specimens examined).

Anterior nostril pierced at tip of an obliquely truncate tube ( Fig. 2 a). Mouth gape about twice as wide as long ( Fig. 3). Lips thick, strongly papillated. A median interruption in lower lip. Processus dentiformis present. No median notch in lower jaw. Inner rostral barbel reaching almost to vertical of anterior margin of eye; outer one reaching vertical of posterior margin of eye. Maxillary barbel reaching middle of postorbital area. Intestine with a loop behind stomach, extending forward to anterior extremity of stomach ( Fig. 4 ).

Sexual dimorphism. Adult males distinguished by presence of a deep slit on cheek (termed suborbital slit), extending from lower margin of eye until above base of posterior rostral barbel ( Fig. 2 a). Infraorbital canal running along ventral edge of slit. No slit in females, but in several of them a shallow groove in similar position ( Fig. 2 b). Smallest individual with a slit (CMK 17777, 63.1 mm SL). Slit and groove homologous to lower margin of suborbital flap in many nemacheilids but not ending posteriorly in a flap. In males, dorsal surface of 5 or 6 anterior branched rays of pectoral fin covered by thick tissue and densely covered by small tubercles (vs. both missing in females); patches of unculi on opercle and suborbital area (vs. absent). Ripe females deeper-bodied.

Coloration. Head and body background colour greyish brown (yellowish brown in material from Mae Khlong drainage, but this apparently induced by water turbidity), whitish on belly; all marks on head and body dark brown, unless mentioned otherwise. Head with 3–4 transverse lines in interorbital and occipital areas, and a few large spots on snout, cheeks and opercle. Dorsum with saddles, 4–5 predorsal, 3–4 subdorsal and 5–6 postdorsal; total 11–16, modally 12 in specimens less than about 65 mm SL, more difficult to count in larger specimens because of ontogenetic changes. In specimens less than about 65 mm SL, saddles with a slightly darker outline; with increasing size, median part of saddle becoming paler and saddles appearing as a pair of dark lines meeting in a pointing tip near lateral line. Anterior saddles oblique, directed backwards; predorsal ones strongly slanted, becoming less slanted along dorsal-fin base, and almost vertical on caudal peduncle. In smaller specimens, at level of lateral line, saddles becoming a very narrow bar, more or less vertical (posteriorly) or slightly slanted (anteriorly); tip of bars at level of pectoral-fin base; only posterior-most bars, at end of caudal peduncle, reaching ventral midline. Between bars, a spot on lateral line and one between tip of bars. In larger specimens, saddles ending at lateral line; below lateral line, bars and spots becoming dissociated and resulting in an irregular mottled pattern. A conspicuous black spot at caudal fin base, vertically elongated, close to upper extremity of fin base; on a pale background but not ocellated.

Dorsal fin hyaline, with 6–7 longitudinal rows of black spots on rays and (usually) membranes. Caudal fin with 6–8 vertical rows of spots on rays and (usually) membranes. Other fins hyaline.

Notes on biology. Two dissected females, CMK 17509, 65.4 mm SL, and CMK 17967, 64.1 mm SL, collected in June 2002 and 2003, respectively, had apparently ripe ovaries with eggs 0.7 mm diameter.

Distribution. Acanthocobitis pictilis is presently known only from the Ataran drainage in Myanmar and the Mae Khlong drainage in Thailand. The two drainages are adjacent and separated by a pass at about 280 masl (Chedi Sam Ong; Three Pagoda Pass). The Ataran drains to the Andaman Sea (Indian Ocean) and the Mae Khlong to the Gulf of Thailand (South China Sea). The Mae Khlong shares a number of genera and species with the Ataran, Salween and Irrawaddy drainages that are not known in any other drainage on the Gulf of Thailand slope (e.g., Batasio , Badis, Rasbora rasbora, Schistura mahnerti , Acanthocobitis zonalternans ; pers. obs. and, e.g., Kottelat 1989, 1990, Ng & Kottelat 2001, Kullander & Britz, 2002).

Etymology. From the Latin pictilis (embroided). An adjective ( pictilis , –is, –e).

Remarks. Earlier authors (e.g. Menon 1987: 141, Kottelat 1990: 31) recognised A. botia ( Hamilton, 1822) as a species distributed in Peninsular India, Sri Lanka, and the Indus, Ganges, Brahmaputra, Irrawaddy, Salween and Mae Khlong drainages in Pakistan, India, Bangladesh, Myanmar, Thailand and China. This was a very heterogeneous assemblage and, among the nominal species listed as synonyms, at least three are valid: A. mooreh (Sykes, 1839) from Peninsular India, A. urophthalmus (Günther, 1868) from Sri Lanka and A. mandalayensis ( Rendahl, 1948) from Myanmar (Kottelat, in press). Some of the nominal species still remaining in the synonymy of A. botia might also be valid. The A. botia specimens from the Mae Khlong drainage reported by Kottelat (1990: 31) are A. pictilis .

Acanthocobitis pictilis shares with A. botia and A. mandalayensis ( Fig. 5 ) the suborbital slit in males (vs. suborbital flap in other species of the genus in Southeast Asia). Its unique colour pattern (see diagnosis) distinguishes it immediately from these two species. Acanthocobitis mandalayensis has saddles along the back and a midlateral row of vertically elongated, slanted, oval blotches along the flank, each blotch connected to a saddle by a narrow band; the blotches, bands and saddles are surrounded by a pale halo contrasting with a dark grey background (in preserved specimens). In most specimens, the halo is so developed that the remainder of the darker background appears as a narrow line, or as a vertically elongated blotch forming a row intercalated between the saddles and the midlateral row of blotches ( Fig. 5 ). In the 'real' A. botia the saddles form a more irregular pattern, the midlateral blotches are roundish to triangular, not elongated, often connected to each other, and connected or not to the saddles, the halo is missing and there is no intercalate row of blotches. Menon (1987: pl. 13 fig. 1, pl. 15 fig. 2), Shrestha (2008: pl. 30 fig. 101), Vishwanath et al. (2007: 98) and Siddiqui et al. (2007: 97) show figures of specimens of A. botia from the Indus, Ganges and Brahmaputra drainages (which may not all be conspecific).

Acanthocobitis pictilis appears in the aquarium-fish literature and on several internet sites as A. rubidipinnis (Blyth, 1860) . Acanthocobitis pictilis is distinguished from A. rubidipinnis in having 12½ or 13½ branched dorsalfin rays (vs. 14½ or 15½), a suborbital slit in males (vs. a suborbital flap) and the distinctive colour pattern (see diagnosis). Acanthocobitis rubidipinnis is known from the lower Irrawaddy; its colour pattern consists of 11–12 vertically elongated blackish blotches on the lateral line and a series of brown saddles along the back, sometimes in contact with midlateral blotches, especially in posterior part of body (see figures in Kottelat 1990: 35, Rendahl 1948: 12).

Kottelat (1990: 35) recognised a third species of Acanthocobitis in Southeast Asia, A. zonalternans (Blyth, 1860) . Its range includes the Brahmaputra drainage in Manipur, the Irrawaddy, Sittang and Salween drainages in Myanmar and Thailand, coastal streams of Tenasserim and the west coast of the Malay Peninsula southwards to Trang, and the Mae Khlong and Tapi drainages. The species also shows a great variety of colour patterns and there are indications that more than one species is confused under this name. Despite its wide range, there is only one synonym, A. phuketensis , from Phuket. Acanthocobitis pictilis is distinguished from A. zonalternans in having a larger size (up to at least 91 mm SL, vs. 44), a complete lateral line (vs. incomplete, reaching between pelvic-fin base and end of dorsal-fin base), 12½ or 13½ branched dorsal-fin rays (vs. 9½ to 11½), a suborbital slit in males (vs. a suborbital flap), 6–7 longitudinal rows of spots on dorsal fin (vs. 3) and 6–8 vertical rows of spots on caudal fin (vs. 4–5). The variable colour pattern of A. zonalternans can be summarised as a row of small saddles alternating with a midlateral row of blotches on flank, the latter sometimes fused into a longitudinal stripe (see Kottelat 1990: 37 for illustrations).

Grant (2007) divided Acanthocobitis into two subgenera, restricting Acanthocobitis to A. pavonacea (M'Clelland, 1839) . He created a subgenus Paracanthocobitis (type species: A. zonalternans ) for the other species placed in Acanthocobitis by earlier authors. The type species of Acanthocobitis is A. longipinnis Peters, 1861 , which Grant considered as a synonym of A. pavonacea (which is open to doubt; Kottelat in press). Grant's ideas were based on his reading of the literature, examination of one living aquarium individual, and of photographs of the poorly preserved holotype of A. longipinnis and of syntypes of Cobitis pavonacea . Without a proper taxonomic study based on personal examination of specimens of all concerned species, it seems neither justifiable nor judicious to recognise names created for no taxonomically justifiable reason. Further, the identity of A. longipinnis (type species of Acanthocobitis ) is not ascertained.

Figures

FIGURE 1. Acanthocobitis pictilis; Myanmar: Ataran drainage; a, CMK 17777, 56.6 mm SL; b, MHNG 2727.066, holotype, 71.8 mm SL.

FIGURE 2. Acanthocobitis pictilis, lateral view of head; a, CMK 17509, 69.6 mm SL, male showing suborbital slit; b, MHNG 2727.066, 71.8 mm SL, holotype, female showing a suborbital fold.

FIGURE 4. Acanthocobitis pictilis, CMK 17967, 64.1 mm SL; digestive tract, ventral view.

FIGURE 5. Acanthocobitis mandalayensis, NRM 36248, 55.7 mm SL; Myanmar: Myitkyina.

Tables

TABLE 1. Morphometric data of Acanthocobitis pictilis, holotype and 16 paratypes (CMK 17519, 17777, 14601, 17249). Ranges include values of holotype.

Standard lenth (mm) Total lenth (mm) In percent of standard length Total length Head length (dorsal)	Ataran drainage holotype range mean 71.8 55.8–80.0 89.2 68.1–101.1 124.3 120.6–127.1 124.2 21.8 20.8–23.4 22.2	Mae Khlong drainage 69.6 69.8 63.0 83.0 85.6 76.9 119.4 122.6 122.1 20.4 20.9 21.8
Head length (lateral) Predorsal length	24.0 22.7–24.9 24.2 47.0 45.2–47.4 46.6	22.4 23.8 24.1 44.9 45.6 47.0
Prepelvic length Pre-anus length Pre-anal length Head depth	52.7 50.0–54.9 52.0 75.2 72.6–76.4 74.3 79.4 77.0–82.6 79.2 13.4 13.2–15.5 14.2	49.9 51.1 53.0 71.3 72.4 72.8 76.9 76.4 79.4 12.9 14.1 14.6
Body depth at dorsal-fin origin Depth of caudal peduncle	17.2 17.2–23.0 19.4 13.0 12.9–14.5 13.5	17.7 19.6 20.4 12.0 13.1 13.6
Length of caudal peduncle Snout length Maximum head width Body width at dorsal-fin origin Eye diameter Interorbital width	14.2 13.7–16.4 15.1 11.4 10.2–11.7 10.9 15.4 14.8–17.7 15.8 13.3 12.1–17.0 13.8 5.4 4.6–6.2 5.5 7.3 6.4–8.3 7.4	15.5 15.8 14.8 10.7 11.0 10.9 14.6 15.6 16.0 12.1 13.1 14.2 5.2 4.5 5.4 6.5 7.6 6.9
Length of dorsal fin Length of upper caudal-fin lobe Length of median caudal-fin ray Length of lower caudal-fin lobe	19.5 15.7–20.9 19.1 23.4 22.1–25.1 23.3 22.5 19.6–25.0 22.2 24.8 21.7–25.7 24.3	18.0 18.4 18.4 20.7 22.5 22.9 19.9 20.2 22.0 21.7 22.5 24.2
Length of anal fin Length of pelvic fin	17.9 15.0–18.4 17.3 17.4 15.7–19.0 17.2	17.0 16.2 17.1 16.2 16.7 16.1
Length of pectoral fin In percent of dorsal head length Snout length Eye diameter Interorbital width In percent of lateral head length	20.4 19.0–22.3 20.5 52 46–54 49.3 25 21–28 24.8 33 29–37 33.2	20.0 19.3 19.6 52 53 50 26 21 25 32 36 32
Snout length Eye diameter Interorbital width	47 41–48 45.1 22 19–26 22.7 30 27–34 30.4	48 46 45 23 19 23 29 32 29