Verlag Dr. Friedrich Pfeil ISSN 0936-9902 Ichthyological Exploration of Freshwaters An international journal for field-orientated ichthyology Volume 22 Number 3 Ichthyological Exploration of Freshwaters An international journal for field-orientated ichthyology Volume 22 • Number 3 • September 2011 pages 193-288, 53 figs., 10 tabs. Managing Editor Maurice Kottelat, Route de la Baroche 12, Case postale 57 CH-2952 Cornol, Switzerland Tel. + 41 32 4623175 · Fax + 41 32 4622259 · E-mail [email protected] Editorial board Pier Giorgio Bianco, Dipartimento di Zoologia, Università, Napoli, Italy Ralf Britz, Department of Zoology, The Natural History Museum, London, United Kingdom Sven O. Kullander, Naturhistoriska Riksmuseet, Stockholm, Sweden Helen K. Larson, Museum and Art Gallery of the Northern Territory, Darwin, Australia Lukas Rüber, Department of Zoology, The Natural History Museum, London, United Kingdom Ivan Sazima, Museu de Zoologia, Unicamp, Campinas, Brazil Paul H. Skelton, South African Institute for Aquatic Biodiversity, Grahamstown, South Africa Tan Heok Hui, Raffles Museum of Biodiversity Research, National University of Singapore, Singapore Ichthyological Exploration of Freshwaters is published quarterly Subscriptions should be addressed to the Publisher: Verlag Dr. Friedrich Pfeil, Wolfratshauser Str. 27, 81379 München, Germany PERSONAL SUBSCRIPTION : EURO 100 per Year/volume - 4 issues (includes surface mail shipping) INSTITUTIONAL SUBSCRIPTION : EURO 180 per Year/volume - 4 issues (includes surface mail shipping) Manuscripts should be addressed to the Managing Editor: Maurice Kottelat, Route de la Baroche 12, Case postale 57, CH -2952 Cornol, Switzerland CIP-Titelaufnahme der Deutschen Bibliothek Ichthyological exploration of freshwaters : an international journal for field-orientated ichthyology. – München : Pfeil. 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Freshwaters, Vol. 22, No. 3, pp. 193-200, 5 figs., 1 tab., September 2011 © 2011 by Verlag Dr. Friedrich Pfeil, München, Germany – ISSN 0936-9902 Schistura diminuta, a new miniature loach from the Mekong River drainage of Cambodia (Teleostei: Nemacheilidae) Chouly Ou*, Carmen G. Montaña*, Kirk O. Winemiller* and Kevin W. Conway*, ** Schistura diminuta, new species, is described from the lower Sekong River, Mekong drainage, Cambodia. It is distinguished from congeners by the following characters: tiny adult body size (maximum known size 19.5 mm SL); lateral line incomplete, with 14-17 pores, terminating on the flank anterior to vertical through pelvic-fin origin; absence of axillary pelvic lobe; processus dentiformis weakly developed; dorsal-fin rays iii-iv.8.i; principal caudal-fin rays 8 + 8 (7 + 7 branched caudal-fin rays); a distinct dark brown spot at centre of caudal-fin base; and 9-10 irregular light brown bars along dorsal body surface. Introduction S. magnifluvis (middle Cambodian Mekong). In addition to these two species of Schistura, Rain- Members of the family Nemacheilidae are small, both (1996) listed four more (S. kengtungensis, benthic fishes, distributed throughout Asia, Eu- S. kohchangensis, S. laterimaculatus and S. nicholsi) rope and the Tana Lake basin of Ethiopia where as probable inhabitants of the Cambodian Me- they mainly inhabit running waters and well kong, given their presence in bordering areas of oxygenated hill streams (Kottelat, 1990). With Thailand, although presence of these latter species close to 200 valid species, the genus Schistura in Cambodia has yet to be confirmed. McClelland is currently the largest and one of the A recent ichthyological survey of the lower most widespread of all the nemacheilid genera Sekong River (one of the three major tributaries (Kottelat, pers. comm.). To date, roughly 70 spe- of the Mekong in Cambodia) in northeastern cies have been described from the Indochinese Cambodia (January, 2010) obtained five tiny region alone (Kottelat, 1990, 1998, 2000; Freyhof specimens of Schistura that differ markedly from & Serov, 2000) with two known to exist in the other species of the genus presently reported from Mekong drainage in Cambodia (Kottelat, 1990; the region. Further investigation has revealed that Rainboth, 1996), viz. S. daubentoni (northern Cam- these specimens represent a new species, which bodian Mekong, including the Sesan River) and is described herein. * Department of Wildlife and Fisheries Sciences, Texas A&M University, 210 Nagle Hall, 2258 TAMU, College Station, TX 77843, USA. ** Corresponding author. Texas Cooperative Wildlife Collection, Department of Wildlife and Fisheries Sciences, Texas A&M University, 210 Nagle Hall, 2258 TAMU, College Station, TX 77843, USA. E-mail: [email protected] Ichthyol. Explor. Freshwaters, Vol. 22, No. 3 194 Materials and methods regular light brown bars along dorsal body sur- face; absence of axillary pelvic lobe; weakly de- Measurements follow Kottelat (1990) except for veloped processus dentiformis; dorsal-fin rays head measurements, which are expressed as a iii-iv.8.i; principal caudal-fin rays 8 + 8 (7 + 7 percentage of lateral head length (HL). Counts branched caudal-fin rays). and osteological terminology follow Conway (2011). Measurements were taken to the nearest Description. General body shape as in Figure 1. 0.1 mm on the left side of specimens using a Zeiss Morphometric and meristic characters listed in DRC stereomicroscope equipped with an ocular Table 1. A miniature species (sensu Weitzman & micrometer. Counts were obtained from the left Vari, 1988), largest specimen examined 19.1 mm side of specimens with the aid of transmitted SL (range 18.0-19.5). Body moderately elongate, light. Specimen photographs were obtained using cross-section circular to slightly compressed an- a Zeiss Stereo Discovery V20 stereomicroscope teriorly, becoming increasingly more oval poste- equipped with an axiocam MRc5. A single rior to dorsal-fin origin. Body depth greatest specimen was cleared and double stained (c&s) midway between occiput and dorsal-fin origin, following the protocol of Taylor & van Dyke (1985) decreasing slightly in depth towards caudal pe- and 4 specimens were radiographed. Only total duncle. Head moderately depressed, cheeks vertebral counts are reported for the holotype and somewhat inflated. Eye relatively large, posi- non-c&s paratype material because it was not tioned high on side of head. Mouth subterminal possible to distinguish between abdominal and and strongly arched (Fig. 2), upper and lower lips caudal vertebrae in the radiographs. Materials fleshy; lower lip with median interruption. Two examined are housed in the following collections: pairs of rostral barbels and one pair of maxillary ZRC, Raffles Museum of Biodiversity Research, barbels present. Inner rostral barbel reaching National University of Singapore, Singapore; slightly past base of outer rostral barbel when TCWC, Texas Cooperative Wildlife Collection, extended; outer rostral barbel reaching slightly Texas A&M University, College Station; IFReDI, past base of maxillary barbel when extended; Fish collection of the Inland Fisheries Research maxillary barbel reaching to or slightly past and Development Institute, Phnom Penh. horizontal through center of eye when extended. Rostral cap poorly developed, not extended as a fleshy flap between base of rostral barbels. Deep Schistura diminuta, new species groove present between upper lip and rostral cap. (Fig. 1) Upper and lower jaws with a sharp horny sheath, processus dentiformis poorly developed. Ante- Holotype. ZRC 53105, female, 18.1 mm SL; Cam- rior nostil situated at tip of a short tube, poste- bodia: Stung Treng province: Mekong River rior edge of opening bordered by a triangular drainage, lower Sekong River in Siem Pang dis- flap; posterior nostril larger than anterior nostril, trict, 14°07'11.88" N 106°23'11.36" E; C. Ou, C. G. situated between base of tube surrounding ante- Montaña, K. O. Winemiller & S. Putrea, 18 Janu- rior nostril and anterior margin of orbit. ary 2010. Dorsal fin with iii.8.i (3) or iv.8.i (1) rays. Anal fin with ii.5.i rays. Principal caudal rays 8 + 8, Paratypes. TCWC 14766.01, 2 (1 c&s), 18.1- branched caudal fin rays 7 + 7. Dorsal procurrent 19.0 mm SL; ZRC 53106, 1, 19.1 mm SL; IFReDI rays 8 (1), 10 (2) or 11 (1), ventral procurrent rays uncatalogued, 1, 19.5 mm SL; same locality as 4 (3) or 5 (1). Pelvic fin with i.5.i rays, pectoral fin holotype. with i.7.ii (2) or i.7.iii rays. Dorsal-fin origin situ- ated slightly posterior to vertical through pelvic- Diagnosis. A miniature species, distinguished fin insertion. Posterior margin of dorsal fin from other members of the genus by the follow- straight to slightly concave. Anal-fin origin