Schistura tenebrosa, Kangrang, Punnatut, Page, Lawrence M. & Beamish, William H., 2012

Kangrang, Punnatut, Page, Lawrence M. & Beamish, William H., 2012, Schistura tenebrosa, a new species of loach from the Kwai Noi River system, Mae Khlong basin, Thailand (Teleostei: Nemacheilidae), Zootaxa 3586, pp. 69-77 : 70-74

Schistura tenebrosa , new species

( Figs. 1–4 )

Holotype. UF 181417, 45.1 mm SL; Thailand, Kanchanaburi Prov., Thong Pha Phum, Mae Khlong basin, Kwai Noi River system, Pakkok River, 14º36'22"N, 98º28'14"E, 5 Dec. 2009, Punnatut Kangrang, Robert Beamish and Thanapoom Kongchaiya.

Paratypes. UF 181418, 10 ex., 33.2–46.0 mm SL; NIFI 4415, 3 ex., 43.6–45.4 mm SL; USNM 400923, 3 ex., 37.4–42.5 mm SL; ZRC 53100, 3 ex., 39.0–45.0 mm SL; same data as holotype. UF 181419, 4 ex., 36.3–44.6 mm SL; same locality as holotype, 5 Dec. 2009, Punnatut Kangrang, Robert Beamish and Thanapoom Kongchaiya. UF 181157, 1 ex., 28.8 mm SL; Thailand, Kanchanaburi Prov., Thong Pha Phum, Mae Khlong basin, Kwai Noi River system, Pakkok River system, Ban Huay Pousa, 14º38'0"N, 98º48'0"E, 20 Apr. 2011, Rungthip Plongsesthee, Randal A. Singer, and Larry M. Page. UF 181420, 4 ex., 42.6–45.9 mm SL; Thailand, Kanchanaburi Prov., Thong Pha Phum, Mae Khlong basin, Kwai Noi River system, Pracham Mai River, 26 Oct. 2010, Rungthip Plongsesthee.

Paragenetype. (UF 181418): GenBank JQ659026 (mitochondrial cytochrome b).

Other material examined. Burapha Univ. uncat., 8 ex., 32.0– 43.8 mm SL; Thailand, Kanchanaburi Prov., Thong Pha Phum, Mae Khlong basin, Kwai Noi River system, Pakkok River, 14º36'52"N, 98º27’53"E, 4 Dec. 2009, Punnatut Kangrang, Robert Beamish and Thanapoom Kongchaiya.

Diagnosis. Member of genus Schistura as defined by Kottelat (1990a). Distinguished from all other species of Schistura by a uniform dusky brown color pattern without marks on dorsum or side of body ( Fig. 1 ) and many conspicuous supplementary neuromasts along the lateral line and on the head. It is further distinguished from other species of Schistura lacking brown or black marks on body by its dark brown color, incomplete lateral line extending only to beneath dorsal fin, and origin of dorsal fin located above origin of pelvic fin.

Description. Body shape and color are shown in Figure 1 . Morphometric data are in Table 1 . Largest specimen is a female, 46.0 mm SL, 55.1 mm TL (UF 181418).

Body compressed, slender, depth slightly greater than body width. Body depth nearly uniform throughout, slightly deeper at dorsal-fin origin than at caudal peduncle. Profile of snout and head moderately pointed. Snout moderately pointed in dorsal view. Head depressed; eye small, oval, longer than high, near dorsal profile, directed dorsolaterally.

Dorsal-fin origin above origin of pelvic fin. Pectoral fin reaching over half distance from pectoral-fin base to pelvic-fin base. Pelvic fin overlapping anus, reaching over half distance from pelvic-fin base to anal-fin origin. Axillary pelvic lobe present. Anal fin not reaching caudal fin. Margins of dorsal and anal fins convex. Caudal fin emarginate. Small adipose crest on dorsal margin, none on ventral margin of caudal peduncle.

Body scaled, except scales absent on nape and on venter before pelvic fins. Scales embedded on anterior side, becoming less so near vertical from origin of dorsal fin. Lateral line incomplete with 18–30 (mean = 24.1; SD = 3.1; mode = 23) pores (n = 35), usually ending before origin of dorsal fin; ending under dorsal fin in one specimen. Dorsal fin iv 7 ½ (n = 27*) or 8½ (n = 1); anal fin iii 5 ½ (n = 28*); pectoral fin 9 (n = 4) or 10 (n = 24*); pelvic fin 8 (n = 28*); caudal fin 9 branched rays in upper half (n = 28*), 7 (n = 2) or 8 (n = 26*) branched rays in lower half.

Lateral line and lateralis system canals on head accompanied by conspicuous supplementary neuromasts ( Fig. 2 ). Supplementary neuromasts occur above and below the lateral-line pores and continue past the end of the lateral line, mostly in clusters of three or four ( Fig. 2 ). Those on head occur mostly along canals. Cephalic lateral-line system with 6 (23), 7 (11) or 8 (1) supraorbital pores; 4+8 (5), 4+9 (20), 4+10 (8) or 4+11(2) infraorbital pores; 7 (1), 8 (1), 9 (4) or 10 (3) preoperculomandibular (countable on only 9 specimens); and 3 (35) supratemporal pores.

Lips moderately thick, pleated, covered with unculi; upper lip with very small median incision; lower lip with median interruption (Fig. 3). Processus dentiformis present. Inner rostral barbel reaching almost to corner of mouth; outer rostral barbel reaching to posterior nostril. Maxillary barbel reaching to or slightly past vertical at rear margin of eye. Barbels covered with unculi. Anterior nostril at base of long pointed flap reaching to eye. Intestine with bend just posterior to stomach, then turning sharply posterior ( Fig. 4). No suborbital flap; no apparent sexual dimorphism.

Color in life. Head and body dark brown dorsally and on side; melanophores densely scattered over all of body except underside of head, breast, and midline of belly creating dusky brown appearance. Underside of head, breast, and belly cream-colored with few or no melanophores; some individuals with a concentration of melanophores on center of breast creating an amorphous blotch. Black preorbital bar extends onto snout nearly to nasal barbel. Barbels cream-colored, without melanophores except at bases.

Most specimens with faint black bar at base of caudal fin. Dorsal fin black at base, black extending up about one-third to one-half length of first ray; dorsal-fin rays lined with black, lighter toward edge of fin; black on rays often darkest in middle of fin creating dusky band. Other fins with melanophores along rays, interradial membranes hyaline. Often a small black spot at posterior end of upper procurrent rays of caudal fin. Characteristic color pattern of adult developed in smallest specimen examined (33.2 mm SL; Fig. 1 ). Specimens preserved in ethanol slightly lighter in color.

Etymology. The name, tenebrosa, Latin adjective for dark or gloomy, is in reference to the dusky color of this species.

Distribution and ecological notes. Schistura tenebrosa is known only from the Kwai Noi, Mae Khlong basin, in the Thong Pha Phum District of Kanchanaburi Province, Thailand ( Fig. 5 ). Most specimens have been found in rubble riffles ( Fig. 6 ) in small streams in the upper reaches of the Pakkok River in the Kwai Noi system. A 45 mm SL female collected on 5 December 2009 had three chironomid larvae (Diptera) and a mayfly (Ephemeroptera) in its stomach and a parasitic nematode in its body cavity. The ovaries of this female and another from the same collection in December had only small ova in their ovaries.

Physical and chemical conditions where S. tenebrosa was captured varied as followed: elevation averaged 430 m asl, stream width was 4.8–7.2 m, depth varied from 18 to 40 cm, velocity varied from 15 to 48 cm /s, and the substrate consisted mostly of small to medium-sized rocks (1–13 cm). Schistura tenebrosa usually was captured where riparian vegetation cover was>50 percent and included mature deciduous trees, screw pines, bamboo, ferns, tall grasses, Alocasias sp. and a variety of other herbaceous plants. Water temperature varied seasonally from 23 to 26 o C. Water pH averaged 7.0. Water chemistry varied little seasonally with oxygen at 8.2 to 8.5 mg /l, ammonia at 0 mg/l, and silica at 3.1–9.8 mg /l. Alkalinity was approximately 10–13 mg /l ( pH 4.5).

Figures

FIGURE 1. Schistura tenebrosa. (A) UF 181417, holotype, 45.1 mm SL, lateral, ventral and dorsal views; (B) UF 181418, paratype, 33.2 mm SL, lateral view. Scale bars = 10 mm.

FIGURE 2. Midlateral view of Schistura tenebrosa, UF 181420, 45.9 mm SL. Scale bar = 1 mm. Lateral-line pores at left have supplementary neuromasts that continue in clusters beyond the end of the lateral line.

FIGURE 5. Distribution of Schistura tenebrosa. Black dots represent localities for specimens examined.

FIGURE 6. Habitat of Schistura tenebrosa. Pakkok River, 14 º 36 ' 22 ' N, 98 º 28 ' 14 " E, Kanchanaburi Prov., 5 December 2009.

Tables

TABLE 1. Morphometric data for Schistura tenebrosa. Data for holotype are included in range and mean. holotype range (N = 36) mean ± SD

Standard length (mm)	45.1	32.0–46.0	41.5±4.0
Percentage of SL
Head length	22.6	20.0–23.9	22.5±0.9
Predorsal length	57.0	50.9–61.3	55.0±2.4
Snout length	9.1	7.0–10.2	8.6±0.7
Prepelvic length	51.0	47.7–55.6	50.6±1.9
Preanal length	79.8	64.2–79.8	73.7±4.5
Body depth	15.3	12.7–18.0	14.5±1.4
Body width	11.8	9.1–14.1	11.8±1.1
Caudal-peduncle depth	13.3	11.4–14.3	12.9±0.8
Caudal-peduncle length	14.6	11.9–16.6	14.8±1.2
Pectoral-fin length	16.0	15.2–17.9	16.6±0.8
Pelvic-fin length	15.1	14.3–17.2	15.7±0.8
Percentage of head length
Eye diameter	9.8	4.7–9.8	7.6±1.3
Interorbital width	28.4	23.7–35.6	27.5±2.4