Pseudecheneis

Heok Hee Ng, 2006, The identity of Pseudecheneis sulcata (M'Clelland, 1842), with descriptions of two new species of rheophilic catfish (Teleostei: Sisoridae) from Nepal and China., Zootaxa 1254, pp. 45-68 : 61-66

[[ Genus Pseudecheneis Blyth ]]

Discussion

Until recently, Pseudecheneis sulcata was thought to be the most widely distributed glyptosternine catfish, being reported to occur in the Ganges, Brahmaputra, Salween, Irrawaddy and Mekong River drainages (Talwar & Jhingran, 1991; Chu & Mo, 1999). Glyptosternine catfishes have restricted distributions, and many apparently wide-ranging species have been shown to consist of more than one species, each with restricted distributions (e.g. Ng & Rainboth, 2001; Ng, 2004). My examination of material from the Tista River drainage (itself a tributary of the Brahmaputra River) and topotypic (or nearly topotypic) material from the Khasi Hills in Meghalaya, India indicates that they are conspecific (no significant differences in biometrics and meristics could be found to distinguish the two populations) and that P. sulcata is restricted to the Brahmaputra River drainage (where it is apparently the only species).

Hora (1937) described a new species and genus, Propseudecheneis tchangi , on the basis of the drawing of a specimen from Yunnan, China in Tchang (1936; reproduced here as Fig. 6). The type locality is listed as "Red River drainage" in the original description. However, Tchang (1936) did not indicate the drainage system from which the holotype of P. tchangi was collected. Zhou & Chu (1992) subsequently synonymized P. tchangi with P. sulcata ( Propseudecheneis having been synonymized with Pseudecheneis by Chu, 1982), speculating that the type locality was in the vicinity of Tengchong (which lies within the Irrawaddy River drainage). There are six river drainages flowing through Yunnan province: the Irrawaddy (=Dayingjiang), Mekong (=Lancangjiang), Pearl (=Zhujiang), Red (=Yuanjiang), Salween (=Nujiang), and Yangtze (=Changjiang) river drainages, and Pseudecheneis has been reported from all but the Pearl and Yangtze River drainages. Of the remaining four river drainages, P. tchangi is unlikely to have come from the Red River drainage (as reported by Hora), since all of the species known from there ( P. intermedius and P. paviei ) have considerably shorter, deeper bodies. This leaves the Irrawaddy, Mekong and Salween river drainages as the possible drainages from which the holotype of P. tchangi was collected. Tchang’s (1936) drawing of the species shows a fish with a uniform dark color, although the species is indicated in the text as having “...some large irregular yellowish blotches...”. The situation is compounded by the fact that at least three species of Pseudecheneis are reported from these three drainages in China (Zhou & Zhou, 2005).

It is unlikely that P. tchangi is conspecific with P. sulcata , since like other glyptosternines, Pseudecheneis species have very restricted distributions (Ng & Edds, 2005; Zhou & Zhou, 2005). Pseudecheneis tchangi was also not collected in the Brahmaputra River drainage (which does not flow through Yunnan province), to which P. sulcata is restricted, further emphasizing the unlikelihood of their conspecificity. However, since I was unable to examine the holotype of P. tchangi directly, I was unable to ascertain which of the three (or more) species recorded from Yunnan is conspecific with the holotype. Therefore, although P. tchangi is tentatively regarded here as a distinct species, comparisons of P. sulcata , P. eddsi and P. stenura with it are restricted to the holotype. As discussed in the diagnoses for each of the three species treated above, P. tchangi differs from P. sulcata , P. eddsi and P. stenura in caudal peduncle depth, pectoral- and pelvic-fin length, and in the number of transverse lamellae on the thoracic adhesive apparatus.

A key character used in diagnosing species of Pseudecheneis is the shape of the first dorsal fin pterygiophore. Two morphological states exist: the absence (Fig. 2a) or presence (Fig. 2b) of a prominent bony spur on the anterodorsal surface of the first dorsal fin pterygiophore. The dorsal surface of this bony spur is co-ossified with the anterior tip of the anterior nuchal plate (itself part of the first dorsal fin pterygiophore). The shape of this element with regards to the presence/absence of the spur is constant within each species (this was verified by examination of radiographs where cleared and stained material was not available) and had been previously used to diagnose P. sulcatoides by Zhou & Chu (1992). It is now found to occur more widely within the genus and its phylogenetic significance is still being investigated.

Externally, P. eddsi is very similar to both P. sulcata , being distinguished from it solely by the length of the pelvic fin. Ng & Edds (2005) also distinguished both P. eddsi and P. sulcata (then combined as P. sulcata ) from both P. crassicauda and P. serracula by the shorter pelvic fins (not reaching base of the first anal-fin ray vs. reaching). The pelvic fin of P. eddsi is even shorter than that of P. sulcata : in the latter, the fin almost reaches the base of the first anal-fin ray, while in the former, the tip of the pelvic fin is separated from the base of the first anal-fin ray by a distance. Furthermore, biplots of the pelvic-fin length against SL for P. eddsi and P. sulcata (Fig. 7) show that the difference is not due to ontogeny alone, as the regression lines are significantly different (ANCOVA, p<0.001). Similarly, biplots of pectoral-fin length against HL (Fig. 8), caudal peduncle length (Fig. 9) and caudal peduncle depth (Fig. 10) against SL for P. stenura vs. P. sulcatus show that the regression lines are all significantly different (ANCOVA; P<0. 001 in all cases).

Artificial key to the species of Pseudecheneis

1. Vertebrae 33-35; typically 8-12 transverse lamellae on thoracic adhesive apparatus ............................. 2

- Vertebrae 36-39; typically 12 or more transverse lamellae on thoracic adhesive apparatus............................................................................................................................... 3

2. Pelvic fins separate (Red River drainage in northern Vietnam and southern China) ...... ........................................................................................................................... P. paviei

- Pelvic fins fused (Mekong River drainage in northern Laos) ................... P. sympelvica

3. Prominent bony spur on anterodorsal surface of first dorsal-fin pterygiophore absent. ....................................................................................................................................... 4

- Prominent bony spur on anterodorsal surface of first dorsal-fin pterygiophore present. ...................................................................................................................................... 5

4. First dorsal element present; complex vertebra with bifid neural spines; length of caudal peduncle 25.0-28.3% SL (Brahmaputra River drainage in India and China) ........... .......................................................................................................................... P. sulcata

- First dorsal element absent; complex vertebra without bifid neural spine; length of caudal peduncle 22.5-23.7% SL (Mekong River drainage in southern China) .............. ................................................................................................................... P. sulcatoides

5. Body uniform color, without pale patches (Mekong River drainage in southern China) .................................................................................................................. P. immaculata

- Body contrasting color, with pale patches ..................................................................... 6

6. Neural spines of last 2-3 preanal and first 6-7 postanal vertebrae strongly elevated; adipose-fin base more than 2.0 times length of anal-fin base (Ganges River drainage in Nepal) ........................................................................................................... P. serracula

- Neural spines of last 2-3 preanal and first 6-7 postanal vertebrae gradually increasing in height; adipose-fin base 1.5-2.0 times length of anal-fin base ................................. 7

7. Caudal peduncle depth 6.0-6.6% SL; eye diameter 7.5-8.3% HL (Ganges River drainage in Nepal) ............................................................................................ P. crassicauda

- Caudal peduncle depth 2.9-5.3% SL; eye diameter 8.3-12.8% HL ............................. 8

8. Pelvic-fin length 18.0-20.9% SL (Ganges River drainage in Nepal) ................. P. eddsi

- Pelvic-fin length 20.4-24.5% SL .................................................................................. 9

9. Caudal peduncle depth 2.9-3.6% SL; pectoral-fin length 160.4-196.9% HL (Irrawaddy River drainage in China) ............................................................ P. stenura

- Caudal peduncle depth 4.0% SL; pectoral-fin length 144.2% HL (Yunnan, China) ...... ......................................................................................................................... P. tchangi