Pangasius mekongensis, Gustiano & Teugels & Pouyaud, 2003

Gustiano, R., Teugels, G. G. & Pouyaud, L., 2003, Revision of the Pangasius kunyit catfish complex, with description of two new species from South-East Asia (Siluriformes; Pangasiidae), Journal of Natural History 37 (3), pp. 357-376 : 370-372

Pangasius mekongensis sp. n.

(figure 7)

Pangasius kunyit (in part) Pouyaud et al., 1999: 251 (specimens from the Mekong Delta). Pangasius n. sp. 1 (in part) Pouyaud et al., 2000: 1513 (specimens from the Mekong).

HOLOTYPE. MZB 10847, 302 mm SL; Binh Dai, Mekong Delta, Vietnam; S. Lenormand; 21 August 1996.

PARATYPES. Twelve specimens: MNHN 2001-0600 , 229–423 mm SL; same data as holotype. Sixteen specimens: MNHN 2001-0601 , 169–225 mm SL; Chau Doc, Mekong Delta, Vietnam; S. Lenormand; 21 August 1996 .

Diagnosis

Pangasius mekongensis is distinguished from all other Pangasius (Pangasius) species by the combination of the following characters: a long head, broad and rounded, with an elongated snout (head length 22.1–26.9% SL; head depth 11.3–13.9% SL; head width 14.8–20.0% SL; snout length 43.4–54.0% HL); the short distance from snout to isthmus (88.4–102.4% SNL); a robust dorsal spine (width 6.6–8.7% HL); the posterior margin of the dorsal spine with 23–25 strong serrae; the pectoral spine with 20–27 strong serrae on posterior margin; the short palatine toothplates (length 6.6–12.8% HL); and the possession of 16–23 gill rakers on the first branchial arch.

Description

Based on the holotype and 28 paratypes. The results of morphometrics taken on the type series are given in table 4.

Head long, broad and rounded in ventral profile and deep anteriorly. Snout long and projected. Anterior nostrils large and entirely situated on anterior margin of upper lip; posterior nostrils located completely on dorsal surface of head; distance between anterior nostrils smaller than distance between posterior nostrils. Premaxillary toothplate visible when mouth closed; vomerine toothplate large and slender, consisting of two separate patches in young, becoming fused ontogenetically; palatine toothplates short and slender throughout the ontogeny; premaxillary and palatine teeth conical; vomerine teeth submolariform. Mouth large and subterminal. Eyes latero-ventrally placed. Maxillary and mandibular barbels reaching beyond eye but not reaching posterior border of operculum. Post-ocular distance short. Distance between tip of snout and isthmus proportionally long. Sixteen to 23 (18 in holotype) short gill rakers on complete first branchial arch. Swimbladder with two or three chambers, extending posteriorly to over anterior half of anal-fin base.

Body robust and broad. First dorsal spine very small; second spine long and robust; dorsal-fin rays six to eight (seven in holotype). Posterior margin of dorsal spine with 23–25 strong serrae; numerous minute serrae on anterior margin. Pectoralfin rays 9–13 (holotype 11). Pectoral spine robust with 20–27 strong serrae on posterior margin and numerous minute serrae on anterior margin. Six soft pelvicfin rays, prepelvic distance proportionally long; pectoral fin not reaching vertical through base of last dorsal fin-ray. Anal fin short with 25–38 soft fin rays (30 in holotype). Adipose fin of notable size, its length about the same as eye diameter. Caudal fin short and somewhat lobed.

Maximum observed size 423 mm SL, but specimens of more than 1000 mm are commonly reported by fishermen in the Mekong Delta.

Coloration

Live specimens generally goldish-coloured on lateral surfaces of head and body and on fins when freshly caught. Lower side of flanks and belly whitish. Upper part of flanks and dorsum darker.

Distribution

Pangasius mekongensis is presently known only from the lower part of the Mekong River ( Vietnam) where it was usually identified as P. djambal , P. bocourti or P. kunyit .

Habitat, ecology, economic importance

Pangasius mekongensis was collected in fresh and brackish waters in the Mekong Delta. This species is piscivorous and is commonly caught with P. krempfi , a species also reported in seawater ( Roberts and Vidthayanon, 1991). The new species has an important commercial value in Vietnam and is considered as a potential aquaculture species and has reproduced in captivity ( Xuan and Liem, 1998; as Pangasius sp. 1).

Etymology Named after the Mekong River Basin, the type locality.