Tachysurus spilotus, Ng, Heok Hee, 2009

Ng, Heok Hee, 2009, Tachysurus spilotus, a new species of catfish from central Vietnam (Teleostei: Bagridae), Zootaxa 2283, pp. 16-28 : 17-22

Tachysurus spilotus , sp. nov.

( Figs. 1 , 2 a, 3a, 4a)

Pelteobagrus fulvidraco (non Richardson, in part) – Serov et al. 2006: 199.

Type material. Holotype: ZRC 51722, 57.8 mm SL; Vietnam: Da Nang province, Song Thuy Loan drainage, Suoi Mo, Ba Na foothills, 16°0'28.8"N 108°2'35.0"E; H. H. Tan et al., 27 February 2005.

Paratypes: ZRC 50574 (15), 30.2–69.3 mm SL; data as for holotype. ZRC 50573 (29), 34.7–63.4 mm SL; Vietnam: Da Nang province, Song Thuy Loan drainage, unnamed feeder stream to Suoi Mo, Ba Na foothills; H. H. Tan et al., 1 March 2005. ZRC 50575 (1), 58.1 mm SL; Vietnam: Da Nang province, stream to Suoi Mo along road from Ba Na to Suoi Mo; H. H. Tan et al., 28 February 2005. UMMZ 245594 (2), 31.7–45.0 mm SL; ZMB 33604 (2), 37.3–43.6 mm SL; ZRC 50277 (1), 41.5 mm SL; Vietnam: Quang Ngai province, Ba Lien River, about 15 km E of Ba To, 14°50'35.4''N 108°49'11.4''E; J. Freyhof, F. Herder & D. V. Serov, 26 February 2000. UMMZ 245595 (3), 44.5–54.8 mm SL; ZMB 33605 (3), 43.0– 59.2 m SL; Vietnam: Binh Dinh province, An Lao River at An Lao, 14°36'9.0''N 108°54'5.4''E; J. Freyhof, F. Herder & D. V. Serov, 22 March 2000.

Diagnosis. Tachysurus spilotus can be distinguished from congeners except T. argentivittatus , T. longispinalis and T. virgatus in having a color pattern consisting of black longitudinal stripes on a pale body (vs. with a uniform-colored body, with pale patches or transverse bands on a dark body, or with dark rectangular patches on a pale body). It differs from T. argentivittatus in having a less bulbous snout ( Fig. 2 ), a notched (vs. uninterrupted) dark dorsal band and gently convex (vs. straight) posterior edges of the caudal-fin lobes; from T. longispinalis in having a shorter dorsal-fin spine (ca. 27% SL vs. 15.1–19.0) and maxillary barbels shorter (vs. longer) than head; and from T. virgatus in having a gently convex (vs. straight) posterior edges of the caudal-fin lobes ( Fig. 3 ), the presence of dark spots at the basal third of the caudal-fin lobes (vs. a dark line running through the middle of each caudal-fin lobe; Fig. 3 ), and a more broadly convex snout when viewed dorsally or ventrally ( Fig. 4 ).

Description. Biometric data in Table 1 . Head slightly compressed; dorsal profile straight, steeply-sloping; ventral profile almost straight; snout slightly bulbous when viewed dorsally and laterally. Bony elements of dorsal surface of head covered with skin and muscle, not readily visible. Midline of cranium with narrow fontanelle extending from level of posterior orbital margin to base of supraoccipital process. Supraoccipital process narrow, with gently converging sides and bifurcate tip, reaching to anterior nuchal plate. Eye ovoid, horizontal axis longest, located entirely in dorsal half of head. Gill openings wide, extending from posttemporal to beyond isthmus.

Mouth subterminal. Oral teeth small, viliform, in irregular rows on all tooth-bearing surfaces. Premaxillary tooth band rounded, of equal width throughout. Dentary tooth band much narrower than premaxillary tooth band at symphysis, tapering laterally. Vomerine tooth band unpaired, continuous across midline, smoothly arched along anterior margin, tapering laterally to point extending posteriorly past level of premaxillary band; band width equal to premaxillary band at midline, narrowing slightly laterally, then tapering to a sharp point posterolaterally.

Barbels in four pairs. Maxillary barbel slender, extending to base of pectoral spine in males, three-quarters distance from its base to base of pectoral spine in females. Nasal barbel slender, extending just beyond vertical through posterior orbital margin. Inner mandibular-barbel origin close to midline; barbel thicker and longer than nasal barbel, extending to half distance between base and base of pectoral spine. Outer mandibular barbel originating posterolateral of inner mandibular barbel, extending to three-quarters distance between base and base of pectoral spine.

Body slightly compressed, becoming more so toward caudal peduncle. Dorsal profile rising evenly and steeply from tip of snout to origin of dorsal fin, sloping gently ventrally from origin of dorsal fin to end of caudal peduncle. Ventral profile slightly convex to anal-fin base, then sloping slightly dorsally to end of caudal peduncle. Skin smooth. Lateral line complete, midlateral in position. Vertebrae 16+20=36 (1), 16+21=37 (1), 17+20=37* (3), 18+19=37 (3), 18+20=38 (5), 19+19=38 (1), 18+21=39 (5) or 19+20=39 (2).

Dorsal fin with spinelet, spine, and 6 (21) rays. Origin of dorsal fin at about two-fifths of body. Dorsal-fin margin slightly convex. Dorsal-fin spine of moderate length, straight, slender, its posterior edge without serrations. Anterior nuchal plate acutely triangular, fitting into bifurcation on posterior tip of supraoccipital process.

Pectoral fin with stout spine, sharply pointed at tip, and 7* (9), 7,i (8) or 8 (4) rays. Anterior spine margin smooth; posterior spine margin with 5–9 large serrae along entire length (serrae fewer in smaller specimens).

Pectoral-fin margin straight anteriorly and posteriorly. Cleithral process narrow, extending two-thirds of pectoral-spine length.

Pelvic-fin origin posterior to vertical through posterior end of dorsal-fin base, with i,5 (21) rays, its margin slightly convex; tip of adpressed fin not reaching anal-fin origin in some individuals, just reaching anal-fin origin in others. Anus and urogenital openings located at vertical through middle of adpressed pelvic fin. Males with a conical genital papilla reaching to base of second anal-fin ray.

Adipose fin with convex margin for entire length, with deeply-incised posterior portion, its anterior origin at vertical through base of first anal-fin ray; adipose-fin base short, spanning one quarter of postdorsal distance. Anal-fin origin at vertical through anterior origin of adipose fin, with iv,10 (2), v,10 (2), vi,10 (2), v,11* (14) or v,12 (1) rays and gently curved posterior margin.

Caudal peduncle moderately deep. Caudal fin deeply forked, with i,7,8,i (21) principal rays; both lobes pointed (with gently convex posterior margin), of equal width. Procurrent rays extend anterior to fin base.

Coloration. In 70% ethanol: Dorsal and lateral surfaces of head predominantly brown, ventral surfaces dark yellow or light brown. Postorbital region with a dark yellow or light brown semilunate mark extending upwards along lower two-thirds of head. Nape with a thin, irregular dark yellow or light brown collar. Body with ventral and lateral surfaces dark yellow or light brown, and brown longitudinal bands on dorsal and lateral surfaces. Dorsal quarter of body with a broad brown stripe extending from anterior to dorsal fin to just anterior to upper procurrent caudal-fin rays. Dorsal stripe partially interrupted by a deep notch posterior to dorsal-fin base, briefly interrupted posterior to adipose-fin base in some individuals. Second brown longitudinal stripe broad, located midlaterally along transverse septum, bifurcating at caudal-fin base. Second stripe joined to first stripe at level of base of dorsal spine and adipose-fin base in some individuals. Third brown longitudinal stripe short, irregular, narrow, located at level of pectoral-fin base and extending from posterior to pectoral-fin base to point just posterior of dorsal fin. Two irregular brown patches present on ventral quarter of body: first one between pelvic- and anal-fin bases, second at anal-fin base; patches coalescent with each other or with third longitudinal stripe in some individuals. Adipose fin brown, with darkyellow or light-brown margin anterodorsally, somewhat hyaline margin posterodorsally. Dorsal fin with brown spot on distal half of first two or three fin rays; rest of fin hyaline. Anal fin with irregular brown marks in middle; rest of fin hyaline. Caudal fin with brown spot on basal third of each lobe; fin rays brown, fin membranes hyaline. Paired fins hyaline. Barbels dark yellow or light brown.

Distribution and habitat. Known only from the short coastal river drainages (Song An Lao, Song Thu Bon and Song Ve) draining the eastern slope of the Annam Cordilleras ( Fig. 5 ), central Vietnam. Tachysurus spilotus inhabits small to medium sized streams and rivers, being more frequently encountered in streams with fast running waters and stony substrate. Other species found at the type locality of P. spilotus include: Puntius semifasciolatus (Cyprinidae) , Zacco sp. ( Cyprinidae ), Sewellia lineolata (Balitoridae) , Sewellia marmorata (Balitoridae) , Cobitis laoensis Cobitidae ), Schistura carbonaria (Nemacheilidae) , Macropodus spechti (Osphronemidae) , Rhinogobius spp. ( Gobiidae ), and Stiphodon sp. ( Gobiidae ).

Etymology. Latinized from the Greek spilotos, meaning spot. The name is an adjective and refers to the spots on the bases of the caudal-fin lobes, a key diagnostic character for this species.

Figures

FIGURE 1. Tachysurus spilotus, holotype, ZRC 51722, 57.8 mm SL; Vietnam: Song Thuy Loan drainage.

FIGURE 2. Lateral views of heads (showing snout shapes) of: a. Tachysurus argentivittatus, UMMZ 248248, 39.6 mm SL; b. T. spilotus, ZRC 50573, paratype, 55.9 mm SL; c. T. virgatus, ZRC 51723, 58.4 mm SL. Images not to scale.

FIGURE 3. Lateral views of caudal fins of: a. Tachysurus spilotus, ZRC 50573, paratype, 55.9 mm SL; b. T. virgatus, ZRC 51723, 58.4 mm SL. Images not to scale.

FIGURE 4. Ventral views of heads of: a. Tachysurus spilotus, ZRC 50573, paratype, 55.9 mm SL; b. T. virgatus, ZRC 51723, 58.4 mm SL. Images not to scale.

FIGURE 5. Map showing collection localities of Tachysurus spilotus.

Tables

TABLE 1. Biometric data for Tachysurus spilotus (n = 25).

	Holotype ZRC 57122	Range	Mean±SD
Standard length (mm)	57.8	31.7–58.6
%SL
Predorsal length	36.8	36.3–40.3	38.1±1.46
Preanal length	62.6	62.6–68.2	65.4±1.65
Prepelvic length	49.9	49.2–52.6	50.5±1.37
Prepectoral length	22.5	21.1–24.4	22.5±1.14
Length of dorsal-fin base	11.7	11.8–14.0	12.6±0.71
Length of dorsal spine	15.7	15.1–19.0	17.0±1.67
Length of anal-fin base	19.9	17.5–20.1	18.8±0.92
Pelvic-fin length	14.7	12.8–15.3	14.2±0.95
Pectoral-fin length	17.6	18.2–23.2	20.1±1.73
Pectoral spine length	14.7	12.0–17.9	15.3±1.34
Caudal-fin length	24.8	21.1–27.9	25.4±2.06
Length of adipose-fin base	12.6	15.8–19.7	17.9±1.00
Dorsal to adipose distance	26.4	18.6–24.8	22.7±2.27
Post-adipose distance	17.7	16.4–18.9	17.7±0.99
Length of caudal peduncle	16.3	16.1–20.7	18.5±1.45
Depth of caudal peduncle	10.1	9.4–10.9	10.2±0.40
Body depth at anus	18.3	15.5–20.1	18.2±1.76
Head length	25.8	25.6–27.8	27.0±0.74
Head width	16.9	17.6–20.1	18.7±0.96
Head depth	17.5	16.3–18.5	17.4±0.80
%HL
Snout length	34.1	31.4–36.0	33.2±1.53
Interorbital distance	38.0	29.0–35.5	32.6±2.42
Eye diameter	22.9	22.6–27.0	25.1±1.29
Nasal barbel length	30.2	29.0–50.3	38.9±8.44
Maxillary barbel length	67.6	56.5–88.5	74.3±10.20
Inner mandibular barbel length	28.5	20.0–41.5	30.4±7.78
Outer mandibular barbel length	40.2	30.0–57.7	44.1±9.90