Hydroécol. Appl. http://www.hydroecologie.org © EDF, 2015 DOI: 10.1051/hydro/2015005

The fishes of the Nam Theun and Xe Bangfai drainages, Laos

Les poissons des bassins de la Nam Theun et de la Xe Bangfai, Laos

M. Kottelat

Aquatic biodiversity specialist, rue des Rauraques 6, 2800 Delémont, Switzerland [email protected]

Abstract – The fish diversity of the Nam Theun and Xe Bangfai drainages was surveyed between 1996 and 2012. 74 species are now recorded from the Nam Theun and 178 from the Xe Bangfai drainages. Twenty-one (28%) of the Nam Theun species are endemic and 9 (5%) of the Xe Bangfai species. At the time of the respective surveys, 54 species were new records for Laos, and 25 species were new to science. While the fish fauna of Xe Bangfai is similar to that of the other main tributaries of the Mekong in Laos, the fish fauna of the Nam Theun is characterised by a great proportion of endemics, several of which have affinities with species known from the opposite slope of the Annamite Range, in Vietnam. Besides, work conducted in relation with aquatic biodiversity surveys for the Nam Theun 2 project resulted in an increase of the fish fauna of Laos from 210 to 481 in 3 years between March 1996 and June 1999 and the discovery of 128 species new to science and lead to the publication of an identification guide. Specific studies have been conducted to assess the status of some of the endemic species that were potentially threatened by the Nam Theun 2 scheme: Sca- phognathops theunensis (still observed in 2012 downstream of Nakai Dam), Tor ater (mainly restricted to streams upstream of the reservoir), and Oryzias sp. 'swamp' (along the fringe of the reservoir). The status of the bitterling Rhodeus laoensis and its associated mussel is still not clear. Most of the species endemic to the Nam Theun drainage are known upstream of the reservoir, which is a protected area. The endemic species known on Nakai Plateau and downstream of the dam are more at risk and require closer monitoring.

Key words – fish diversity, Mekong tributaries, endemism, hydropower project

Résumé – La diversité ichtyologique des bassins de la Nam Theun et de la Xe Bangfai a été suivie entre 1996 et 2012. 74 espèces sont maintenant recensées pour le bassin de la Nam Theun et 178 pour le bassin de la Xe Bangfai. Vingt-et-une (28 %) des espèces de la Nam Theun y sont endémiques et 9 (5 %) de celles de la Xe Bangfai. Au moment des inventaires respectifs, 54 espèces ont été ajoutées à la liste des espèces connues au Laos, et 25 espèces étaient nouvelles pour la science. Alors que la faune ichtyologique de la Xe Bangfai est similaire à celle des autres principaux affluents du Mékong au Laos, la Nam Theun est caractérisée 2 M. Kottelat par une grande proportion d’espèces endémiques, plusieurs de ces espèces présentant des affinités avec les espèces connues du versant opposé de la chaîne annamitique, au Vietnam. De plus, les travaux d'inventaire de la biodiversité aquatique conduits en relation avec le projet de Nam Theun 2 ont fait passer la faune ichtyologique du Laos de 210 à 481 espèces en 3 ans entre mars 1996 et juin 1999 ; ils ont mené à la découverte de 128 espèces nouvelles pour la science et à la publication d'un guide d'identification. Des études spécifiques ont été conduites afin d’évaluer le statut de quelques espèces endémiques potentiellement mena- cées par le projet hydroélectrique de Nam Theun 2 : Scaphognathops theunensis (encore observée à l’aval du barrage en 2012), Tor ater (restreinte principalement aux affluents en amont du réservoir), et Oryzias sp. 'swamp' (sur les bords du réservoir). Le statut de la bou- vière Rhodeus laoensis et de la moule associée à son cycle biologique n’est pas encore cla- rifié. La plupart des espèces endémiques de la Nam Theun sont connues en amont du réservoir, qui est une zone protégée. Les espèces endémiques connues du plateau de Nakai et en aval du réservoir sont plus menacées et nécessitent un suivi attentif.

Mots clés – diversité ichtyologique, affluents du Mékong, endémisme, projet hydroélec- trique

1 INTRODUCTION suppression of a part of the habitats in the reservoir and downstream of a dam The diversity of inland fishes in or downstream of a diversion channel, Southeast Asia is very high, with about or the interruption of migratory road, 3000 named species (Kottelat, 2013b). and must be addressed and mitigated at Despite this high diversity and their the conception of the project. In areas importance for humans, our knowledge whose fish fauna is still superficially of fish biology over most of Asia is still known (as is the case in most of Laos), very incomplete and often is restricted extensive surveys and collection of to mere lists (Kottelat & Whitten, 1996). baseline data is an absolute necessity. Large areas are still unsurveyed. The surveys should not be restricted to In a review of the conservation sta- the directly impacted area but must tus of fish in mainland Southeast Asia, include adjacent areas, in as well as Kottelat et al.(2012a) reviewed the outside the impacted river system. major threats affecting freshwater The information on Laotian fishes fishes. They found that alteration of river published in the scientific literature is morphology is the single most important still very limited. Proper scientific sur- threat since it modifies or suppresses veys of the fish diversity started in the the habitats and the hydrological fea- mid-1990s in conjunction with hydro- tures upon which the fish depend. power development. Without underes- Among these alterations, the develop- timating the environmental impacts of ment of dams and reservoirs is the most the project, surveys conducted in the crucial threat. framework of the Nam Theun 2 project A number of the impacts are intrinsic are unique in Laos for various extents: to the creation of reservoirs, like the (i) the baseline studies that have been The fishes of the Nam Theun and Xe Bangfai drainages, Laos 3 conducted before construction, (ii) the example Microcobitis aff. misgurnoides quantity of information that have been is distinct but close to Microcobitis mis- assembled, made publicly accessible gurnoides. The term “cf." indicates that and that have been used for scientific the population is likely to belong to the research. species referred to but the identification This essay briefly presents the is not yet certain because of unresolved researches that have been conducted taxonomic problems. between 1996 and 2012, the fish fauna In the discussion, endemic is used of the Nam Theun and Xe Bangfai as either a noun or an adjective means: drainages and the status of the species whose distribution is restricted to a geo- of special concern. graphically limited area. For example, a species endemic to the Nam Theun is a species that has been observed only 2 METHODS AND TERMINOLOGY in the Nam Theun drainage. Spelling of names of villages, moun- Over the years, fish samples were tains, and streams follow either the obtained with almost all possible meth- NTPC standard toponymy or the 1985 ods: electricity, gill nets, castnets, 1:100,000 Lao P.D.R. topographic seines, pushnets, kicknets, hook and maps. Coordinates were obtained from line, traps, spears, and ichthyocides. maps in the early years and with a vari- Explosives were never used although ety of GPS after 2000. Datum: WGS 84, fishes killed by poachers have occa- UTM zone 48. sionally been observed. All possible Limitations. Ideally, we should be existing habitats have been surveyed, able to select more or less random sites including headwaters, riffles, runs, for survey. This is rarely feasible for dif- deep pools, main rivers, waterfalls, rap- ferent reasons, among which: (i) the ids, swamps, lakes and caves. Sam- places were the river is accessible by pling sites of very difficult accesses, up land may not be suitable for sampling; in the Annamite range or in the gorges (ii) it may be impossible to land by boat were reached by helicopter. Surveys at a given site; (iii) the presence of a vil- were conducted in 1996, 2002, 2003, lage or a fishing camp does not allow 2006, 2007, 2009, 2011 and 2012. the use of some methods; (iv) or the Samples were obtained at 243 sites; available equipment does not allow most sites were sampled once, but good sampling of large rivers or deep some were sampled by up to 5 surveys. waters, or very fast current. These lim- Species are recorded only under itations are most obvious for the work in their scientific names (see Kottelat, the lower Nam Theun (downstream of 2013b for the latest update of the the Nakai Dam), several stretches of nomenclature of the fishes of freshwa- which can only be accessed by helicop- ters in Southeast Asia). The term "sp." ter (as done in 1996, 2006 and 2007) or means an unidentified species. The by long walks along dangerous shores, term "aff." means that a population can- which is not possible with heavy equip- not be identified with any known species ment. The number of places allowing a but is close to a named species (for safe access to the river is limited, and 4 M. Kottelat then one needs to be able to safely by Pellegrin (1936) and Pellegrin & move around, to find a spot where it is Fang (1940). possible to set (and recover) nets, to Sérène (1951) compiled a first list of apply chemicals, to recover the sam- the fishes of Laos and Taki (1974) pub- ples. Safety is a very important limita- lished a book summarising the known tion because of the very strong current, fauna and its distribution. However, slippery rocks, etc. the published scientific data on fish Conventions. Upper Nam Theun distribution and biology were virtually refers to the Nam Theun River restricted to the Mekong mainstream upstream of the Nakai Reservoir. Lower (Kottelat, 1989; Roberts, 1993). Except Nam Theun refers to the Nam Theun for limited data on the Nam Ngum 1 River downstream of the Nakai Dam. Reservoir and isolated descriptions of Keng Louang: in Laos, most rapids new species there was no data on the have a proper name, and on many riv- fish fauna of the tributaries and head- ers there is one or more called Keng waters. Louang (literally "large rapids"). The A first survey of the fishes of the Nam Theun has two Keng Louang, one Nam Theun and Xe Bangfai was very far downstream of the reservoir, the superficial, with about 54 species other at about FSL (Full Supply Level). observed, with numerous identification The Nam Xot has one Keng Louang, problems. below FSL. As of March 1996, about 210 fish NPA stands for National Protected species were known from Laos. The Area, as used here it implies the first survey of the fishes of the Nam Nakai–Nam Theun NPA. Theun and Xe Bangfai yielded 165 SL stands for standard length (the species (Kottelat, 1996), which is equal length of a fish without the caudal fin); to 79% of what was known before for masl for meters above sea level. the whole country. In fact 46 of these species had not been recorded before in the country. In one month the fish 3 FISH SURVEYS: CHRONOLOGY fauna of Laos had increased to 256 AND SIGNIFICANCE OF NAM THEUN species. Several of these 46 species 2 PROJECT ON KNOWLEDGE were known from Thailand, Vietnam or OF LAOTIAN FISH FAUNA China, but 16 were apparently new to science and ipso facto endemic to the The first mention of fishes of Laos in Nam Theun 2 project area. the scientific literature dates back to The next year, surveys were con- 1878 when Sauvage (1878, 1880) ducted in order to try to find these 16 described a few fishes collected by endemics outside the project area Jules Harmand (Kottelat, 1984). (Kottelat, 1997). The Xe Banghiang Nothing else was published until the (the drainage immediately South of the 1930s, when some fishes were col- Xe Bangfai) was surveyed. For safety lected during ornithological expeditions and logistics reason it was no possible by J. Delacour (Hennache & Dickinson, to survey the Nam Kading and Nam 2000; Kottelat, 2012c: 51) and described Xan immediately north of the Nam The fishes of the Nam Theun and Xe Bangfai drainages, Laos 5

Theun, and rivers were surveyed fur- had obtained on Nakai Plateau. The ther North in Laos. These surveys 1999 survey also found more of the obtained 233 fish species in 5 weeks, 'endemic' species outside the Nam that is, about as many species that Theun 2 project area and further taxo- were already known in the country after nomic research revealed that some of the 1996 survey. The surveys added the species identified in 1996 were in 55 species to the fauna of Laos, of fact a mixture of several species. In which 35 were new to science. The sur- 2002, two species remained (Scaphog- veys also discovered some of the puta- nathops theunensis, Tor ater) that tive endemics in the Xe Banghiang and were known only from the impacted they also allowed to show that most of area and surveys were conducted in the species endemic to the project area 2002 and 2003 to try to find them out- were present upstream of the impacted side the impacted area and to obtain area. information on their biology and life In 1999 I was asked to compile the cycle (Kottelat, 2002, 2004). reports of the surveys conducted for With the start of the construction Nam Theun 2 and other projects into a phase of the Nam Theun 2 project, addi- guide to the fishes of Laos. This project tional surveys were conducted in 2006, was supported by a grant from World 2007, 2009 and 2012 to collect base- Bank/Netherlands Partnership Pro- line data and for monitoring (Kottelat, gram. In order to have a more complete 2006, 2007, 2009, 2013a). coverage, several additional drainages The surveys done in connection with were surveyed. These surveys as well the Nam Theun 2 project contributed as works of other researchers (e.g. directly or indirectly to the documenta- Baird et al., 1999) brought the fish tion of more than half of the fish fauna fauna of Laos to 481 species (Kottelat, of Laos. Fish surveys have been con- 2001). From 210 species in March ducted for other hydropower projects in 1996 and to 481 in June 1999, the fish the country. Most are not publicly avail- fauna of Laos had increased by 228%. able, or are not usable. Only very few These surveys allowed the discovery of other surveys produced data that resulted 128 species new to science (Kottelat, in scientific publications (Roberts, 1995, 1998, 2000; Ng & Kottelat, 1998, 1999, 1997, 1998a; Baird et al., 1999). 2000a-c; Ng, 1999a-b; Chen et al., 1999; Kottelat & Bréhier, 1999; Fang & Kottelat, 1999, 2000; Britz & Kottelat, 4 THE STUDY AREA 1999a-b; Kottelat & Ng, 1999; Chen & Kottelat, 2000). The investigated area covers the Since, species continued to be drainages of the Nam Theun and Xe added by other surveys and other Bangfai (Fig. 1). The Xe Bangfai is an researchers and the total fish fauna of east-side tributary of the Mekong, Laos is now about 520. entering it about 50 km south of Tha- After the 1996 survey of Nam khek. The Nam Theun is adjacent to the Theun 2 project area, Roberts (1998b, Xe Bangfgai to the North; it joins the 1999) described additional species he Nam Gnouang to constitute the Nam 6 M. Kottelat

Fig. 1. Map of Nam Theun and Xe Bangfai drainages showing sites sampled by fish biodiversity sur- veys between 1996 and 2012. Fig. 1. Carte des bassins de la Nam Theun et la Xe Bangfai montrant les sites échantillonnés par les inventaires ichtyologiques entre 1996 et 2012. The fishes of the Nam Theun and Xe Bangfai drainages, Laos 7

Kading, another large east-side tribu- in the dry season only mud pools and a tary of the Mekong, entering it south of few deeper lakes subsisted. Paksan. Although adjacent, the two riv- The Nam Theun leaves the Nakai ers have different topography, which is Plateau through long and narrow reflected by different fish fauna. gorges. In this stretch, until 2008, the Nam Theun was a succession of rapids 4.1 Nam Theun and a waterfall (that disappeared in the rainy season). Along this stretch the The Nam Theun and its tributaries Nam Theun receives a single tributary (the main ones are Nam On, Nam Noy, (Nam Phao), which also originates on Nam Mon, Nam Xot and Nam Nian) the Laos-Vietnam border and also originate on the Laos-Vietnam bound- flows parallel to the other Nam Theun ary, 1000-2200 masl, and flow perpen- tributaries. The Nam Theun has no sig- dicular to it, northeast-southwest. These nificant tributaries on the left side. rivers have a high gradient and are About 70 km after leaving the Nakai interrupted by many large rapids and Plateau, the Nam Theun joins the Nam waterfalls. Their bed is mainly made of Gnouang (another river descending large blocks, boulders and stones, from the Laos-Vietnam divide) and they except for a threshold of a few km at become the Nam Kading. The Nam about 560 masl with relatively slow Kading enters again gorges for about water, with sandy bottom and shores. 70 km to reach the lowland, and then From there, the Nam Theun and its trib- the Mekong. Shortly downstream of the utaries descend to Nakai Plateau confluence of the Nam Theun and Nam through deep and steep gorges, in a Gnouang, a dam created the Theun- succession of rapids (now flooded, at Hinboun Reservoir and diverts part of least part of the year). the waters of the Nam Kading to the The Nam Theun and its tributaries Nam Hinboun, another tributary of the flow parallel to each other until they Mekong; an extension dam on the Nam reach Nakai Plateau. Although the pla- Gnouang stocks more water for the teau is quite flat (altitude about 530 masl) Theun-Hinboun Reservoir. and has only a very shallow ridge above a steep slope directed northeast-south- west, the Nam Theun makes a sharp 4.2 Xe Bangfai right angle turn northwest and is joined by its tributaries. The Xe Bangfai topography is very The Nam Theun meanders on the different from that of the Nam Theun. plateau in a succession of relatively The sources of the Xe Bangfai are slow runs, shallow rapids and deep located along the Laos-Vietnam bound- pools. The substrate varies from sand ary at about 17°N 106°30'E. The alti- (especially at mouth of tributaries, e.g. tude of that area is around 700 masl. It Nam Xot, Nam On) to rocks. The water first flows southeast-northwest, in a was usually clear in the dry season. quite narrow valley and through two An extensive area of the plateau was deeply dissected limestone areas. It naturally flooded in the wet season, but has a typical morphology of highland 8 M. Kottelat river, with a bed made of stones and and that most of them are temporary or boulders. It has nowhere a strong gra- have water only in their lowermost dient and no large rapids or waterfall course. Also, because of the karstic for- could be seen from the air. After about mations and the absence of surface 70 km it disappears in a natural tunnel. water, most of the middle and lower Xe The distance between the entrance of Bangfai drainage is characterised by the tunnel and the resurgence is about large quantities of sand and dust in the 5 km at the surface. The tunnel is known dry season, a phenomenon already to foreigners since Cupet (1900: 191, reported in the first published descrip- map 8). Contrary to some other natural tion of the area (Cupet, 1900: 185). tunnels in the Khammouane karst it has The karst massive is very extensive numerous waterfalls and cannot be and is shared with the Xe Done and travelled by boat or used as passage Nam Hinboun drainages and also between two valleys. Nevertheless, it extends to Vietnam. Beside the Xe has been crossed as early as 1905 Bangfai tunnel already mentioned, sev- (Macey, 1908, 1911) and since it has eral streams have underground courses. been mapped and explored (Mouret Numerous caves have already been et al., 1996, 1997a-b, 2010; Pollack & explored and a number of troglobyte Osburn, 2006; Pollack et al., 2009). animals have been discovered, includ- From the resurgence, the Xe Bang- ing three species of fishes (Kottelat & fai flows west until about Mahaxai, Bréhier, 1999; Kottelat & Steiner, 2011; across a plain with several massives of Vidthayanon & Jarutanin, 2002). tower karst. On this plain, before reach- ing the area of the Nam Theun 2 project, the Xe Bangfai was a large, rel- 5 FISH FAUNA atively shallow and slow flowing river, interrupted only by a few shallow rap- The species now known to occur in ids. In 1996 the water was clear as far the Nam Theun and Xe Bangfai drain- as downstream of Mahaxai; this was no ages and their distribution outside these longer the case in 2006, with increased drainages are given in Appendix 1. human activity. Downstream of Mahaxai, the Xe Bangfai turns southwards and enters a hill range where it goes 5.1 Nam Theun drainage through various rapids, none of signifi- cant size, and at least one very deep Seventy-four fish species have pool. After the gorges, it enters the been recorded in the Nam Theun and Mekong floodplain and the Mekong Nam Gnouang drainages. The two riv- itself. ers join to form the Nam Kading. The The Xe Bangfai has two main tribu- fish fauna of the Nam Gnouang is still taries, the Xe Noy and Nam Oula, which incompletely surveyed but for what is are shallow slow flowing streams. On known, in the lowermost section, it is most of its course, the Xe Bangfai flows identical to that of the Nam Theun in karstic formations, which explains (from data of the 1996 and 2002 sur- that it has very few surface tributaries, veys). The fauna of the upper part of The fishes of the Nam Theun and Xe Bangfai drainages, Laos 9 the Nam Gnouang drainage, however, National Protected Area (NPA), upstream could differ from that of the Nam of the last village. Theun. More surveys may have been The first survey in 1996 recorded 60 conducted for other projects but the species in the Nam Theun. The follow- data have not been made public. The ing surveys added 14 species. Even list of the native species recorded in the 2012 still added 2 species. This the Nam Theun is presented in Table I. suggests that additional surveys still The fauna of the Nam Theun is might add a few species. The number peculiar by its high proportion of of potential additional species in the endemic species, 21 out of 74 (28%). upper Nam Theun is probably very low. Noteworthy, a number of these endem- This is not the case for the lowermost ics belong to genera known from the stretch. The two additional species eastern slope of the Annamitic range, recorded by the 2012 survey were in Vietnam and in southern China (e.g. obtained in the lower Nam Theun Rhodeus laoensis, Microcobitis aff. (Ambastaia nigrolineata, Puntioplites misgurnoides), which is a distinct falcifer). It is not clear whether the zoogeographic unit. Other species are increase of the number of species in not known from elsewhere in the the lower Nam Theun is due to a less Mekong drainage but are widely dis- intensive sampling because of the tributed in Vietnam and South China more difficult (and expensive) access, (e.g. Hemibarbus cf. umbrifer). Pres- or if it is the result of species from the ently there is no hypothesis explaining slow flowing waters from near the this distribution pattern. Theun–Hinboun Reservoir now being Another example of an East Asian able to move upstream because of the species present in the Nam Theun very much reduced flow (e.g., Param- drainage is Misgurnus anguillicaudatus bassis sp. 'slender'). Exotic species presently known only from near Ban have also appeared in the reservoir Nape (on Nam Phao upstream of Lak and some have the potential to become Sao). This species inhabits swamps invasive (e.g. Parambassis siamensis, and rice paddies and can be trans- Cottet et al., same issue). ported out of water for a long period and Although most of the species origi- it could have been transported by nally recorded on Nakai Plateau have humans across the divide. If the species disappeared after inundation, all have is not native, the introduction must have been observed since, upstream or happened at least 50 years ago since downstream of the reservoir. The single older persons interviewed in villages exception is Pangio aff. fusca, which is commented that the species has not conclusive since the species had always been present. The other 'Viet- been collected only in 1996 in crevices, namese' species are less likely to have an habitat difficult to sample. The later been introduced by humans since they surveys, before and after construction would not survive the transport, they are of the dam did not obtain that species. of no special food interest, and they Whether all the species endemic to were found only far up in the tributaries the Nam Theun drainage will be able of the Nakai Reservoir, in the Nakai to maintain over time is still an open 10 M. Kottelat

Table I. Native fish species recorded in the Nam Theun drainage, their general distribution outside Nam Theun, the level of knowledge of their biology, and their biodiversity importance. Biology: 0 = unknown; 1 = partly known; 2 = known. Distribution: a = widely distributed in Southeast Asia; b = widely distributed in Mekong drainage; c = widely distributed and/or abundant upstream of the inundation zone or in other tributaries of the Nam Theun; d = range totally or largely in inundation zone and/or in Nam Theun down- stream. Tableau I. Poissons indigènes recensés dans le bassin de la Nam Theun, leur distribution générale en dehors du bassin de la Nam Theun, le degré de connaissance de leur biologie et leur importance en termes de biodiversité. Biologie : 0 = inconnue ; 1 = partiellement connue ; 2 = connue. Distribution : a = espèce largement distribuée en Asie du Sud-Est ; b = espèce largement distribuée dans le bassin du Mékong ; c = espèce largement distribuée et/ou abondante en amont de la zone d’inondation ou dans d’autres affluents de la Nam Theun ; d = espèce totalement ou en partie présente dans la zone d’inondation et/ou dans la Nam Theun en aval.

Biodiversity General distribution Biology importance in context Distribution (raw outline) of present report less abcd important important Anguillidae 1 x x Indo-West Pacific; Anguilla marmorata (?) occasional in Mekong Cyprinidae Amblypharyngodon 1 x x Mainland Southeast Asia chulabornae 0 x x Nam Theun - Nam Bangana elegans Gnouang endemic Barbodes aurotaeniatus 0 x x Mekong drainage Cyclocheilichthys armatus 1 x x Southeast Asia Cyclocheilichthys repasson 1 x x Southeast Asia 0 x x Nam Theun - Nam Devario fangfangae Gnouang endemic Esomus metallicus 1 x x Mainland Southeast Asia Folifer cf. brevifilis 0 x x Southeast and East Asia Garra cambodgiensis 0 x x Mainland Southeast Asia Garra cyrano 0 x x Middle Mekong drainage Garra theunensis 0 x x Middle Mekong drainage Hampala macrolepidota 1 x x Southeast Asia Hemibarbus cf. umbrifer 0 x x East Asia Hemiculterella macrolepis 0 x x Middle Mekong drainage Hypsibarbus vernayi 1 x x Mainland Southeast Asia Luciocyprinus striolatus 0 x x Middle Mekong drainage Mystacoleucus marginatus 1 x x Southeast Asia Neolissochilus blanci 0 x x Mekong dbasin Onychostoma fusiforme 0 x x Middle Mekong drainage 0 x x Middle Mekong and Poropuntius carinatus Salween drainages Puntioplites falcifer 1 x x Mekong drainage Puntius brevis 0 x x Southeast Asia The fishes of the Nam Theun and Xe Bangfai drainages, Laos 11

Table I. Continued. Tableau I. Suite. Biodiversity General distribution Biology importance in context Distribution (raw outline) of present report less abcd important important Raiamas guttatus 0 x x Southeast Asia Rasbora paviana 0 x x Mainland Southeast Asia Rhodeus laoensis 0 x x Nam Theun endemic Scaphiodonichthys 0 x x Mekong and Chao Phraya acanthopterus drainages 0 x x Nam Theun - Nam Scaphognathops theunensis Gnouang endemic Tor ater 0 x x Nam Theun endemic Tor laterivittatus 0 x x Middle Mekong drainage Tor tambra 0 x x Southeast Asia Tor tambroides 0 x x Southeast Asia Gyrinocheilidae Gyrinocheilus aymonieri 1 x x Mainland Southeast Asia Balitoridae Balitora lancangjiangensis 0 x x Middle Mekong drainage Balitoropsis yunnanensis 0 x x Mekong basin Hemimyzon papilio 0 x x Middle Mekong drainage Homalopteroides smithi 0 x x Mainland Southeast Asia Nemacheilidae Nemacheilus arenicolus 0 x x Nam Theun endemic Schistura atra 0 x x Nam Theun endemic Schistura cataracta 0 x x Nam Theun endemic Schistura dorsizona 0 x x Middle Mekong drainage Schistura kongphengi 0 x x Middle Mekong drainage Schistura nudidorsum 0 x x Nam Theun endemic Schistura obeini 0 x x Nam Theun endemic Schistura sombooni 0 x x Middle Mekong drainage Schistura tubulinaris 0 x x Nam Theun endemic Cobitidae Lepidocephalichthys hasselti 0 x x Southeast Asia Microcobitis aff. 0 x x Nam Theun-Nam misgurnoides Gnouang endemic Misgurnus anguillicaudatus 2 x x East Asia Pangio aff. fusca 0 x x Nam Theun endemic Botiidae 0 x x Mekong and Chao Phraya Ambastaia nigrolineata basins Bagridae Hemibagrus wyckioides 1 x x Mekong drainage Pseudomystus siamensis 0 x x Mainland Southeast Asia 12 M. Kottelat

Table I. Continued. Tableau I. Suite.

Biodiversity General distribution Biology importance in context Distribution (raw outline) of present report less abcd important important Siluridae Pterocryptis inusitata 0 x x Nam Theun endemic Clariidae Clarias cf. batrachus 3 x x Southeast Asia Sisoridae Bagarius yarrelli 1 x x Southeast and South Asia Glyptothorax horai 0 x x Middle Mekong drainage 0 x x Mekong and Chao Phraya Glyptothorax laosensis drainages Glyptothorax aff. zanaensis 0 x x Middle Mekong drainages Oreoglanis hypsiurus 0 x x Nam Theun endemic Oreoglanis lepturus 0 x x Nam Theun endemic Pseudechenei sympelvica 0 x x Mekong basin Adrianichthyidae Oryzias pectoralis 0 x x Nam Theun endemic Oryzias sp. 'river' 0 x x Nam Theun endemic Oryzias sp. 'swamp' 1 x x Nam Theun endemic Synbranchidae Monopterus javanensis 2 x x Southeast and East Asia Ambassidae Parambassis sp. 'slender' 0 x ? x Nam Theun endemic ? Odontobutidae Neodontobutis aurarmus 0 x x Mekong basin Gobiidae Papuligobius ocellatus 0 x x Mekong basin Rhinogobius lineatus 0 x x Nam Theun endemic Anabantidae Anabas testudineus 2 x x Southeast and South Asia Osphronemidae Trichopsis schalleri 1 ? x Mekong basin Channidae Channa gachua 1 x x Southeast Asia Channa striata 2 x x Southeast and South Asia Mastacembelidae Mastacembelus armatus 0 x x Southeast and South Asia The fishes of the Nam Theun and Xe Bangfai drainages, Laos 13

Table II. Fish species endemic to the Xe Bangfai drainage and their biodiversity importance. a = range totally or mainly in NTPC area;b=range exclusively or mainly upstream of NTPC activities. Tableau II. Espèces de poissons endémiques au bassin de la Xe Bangfai et leur importance en termes de biodiversité. a = espèce totalement ou principalement présente dans la zone de NTPC ; b = espèce présente exclusivement ou principalement en amont des activités de NTPC. Biodiversity importance in context of present Distribution report less ab important important Cyprinidae Bangana musaei * x x cave species found in Xe Bangfai tunnel Devario sp. 'green' x x Nam Kathang Gnai Devario cf. quangbinhensis ? x ? x Nam Oula Nemacheilidae Schistura punctifasciata xx Schistura sp. 'Nam Kathang' x x Nam Kathang Gnai Cobitidae Acantopsis sp. 'dwarf males' ? x ? x Lower Xe Bangfai Acantopsis sp. 'vertical spots' ? x ? x Nam Oula Sisoridae Glyptothorax aff. fuscus 2xxXeNoy Odontobutidae Terateleotris aspro x x Upper Xe Bangfai * Bangana musaei is a biodiversity very important species with an extremely small range in the cave system of the underground course of the Xe Bangfai. It is however totally outside the impact zone of NTPC activities. question. Most concerned species are Xe Kong in the South until the Nam Scaphognathops theunensis, Oryzias Ngum in the North, at least in the flood- sp. 'swamp', and Rhodeus laoensis. plain. Those of these rivers that have Luciocyprinus striolatus, a rare and glo- been studied tend to have distinctive bally endangered species, is also of fauna in the upper stretches. A single special concern. site could be efficiently sampled in the upper stretch of the Xe Bangfai 5.2 Xe Bangfai drainage (upstream of its underground course). Only 9 species are apparently endemic 178 species have been recorded in to the Xe Bangfai (Tab. II). Only one of the Xe Bangfai drainage (Appendix 1). the species very similar to or possibly The fauna of the Xe Bangfai is similar shared with Vietnam (Devario aff. to that reported for the other main trib- quangbinhensis) is of biodiversity impor- utaries of the Mekong in Laos, from the tance (small distribution range). 14 M. Kottelat

The Xe Bangfai drainage has a typ- catchment, considering the morphology ical Mekong floodplain fish fauna. A and functioning of karst systems, the number of these Mekong species have actual range of the species may extend not yet been recorded in the Xe Bangfai for a long distance and the species but are expected to be present. The could potentially be impacted by the 2012 survey included habitats that had project, especially by surface pollution not been sampled before (because they and lowering of the water table. were not directly impacted by the Nam Theun 2 operations). Four days of sam- pling (7 sites) yielded 29 additional spe- 6 BIODIVERSITY IMPORTANT SPECIES cies. Most were from tributaries and swamps. Four of these additional spe- cies are presently known only from the 6.1 Rationale for focusing on Xe Bangfai; some will certainly be dis- biodiversity important species covered in adjacent drainages but oth- ers are potentially endemic and biodi- In the context of the impact of a versity important (Tab. II). Five of the Xe project on aquatic biodiversity, some Bangfai endemics have their known species have a greater biodiversity range entirely or partly upstream of the importance than others, either because: area directly impacted by Nam Theun 2 - their range is totally or largely impacted activities. by the project; or a part of their range vital at a period of their life-history cycle is totally or largely impacted by the 5.3 Cave fishes project (for example an obligatory and The Xe Bangfai crosses several unique breeding site); extensive karst massives. Several fish - although they may have a large range species have been observed in caves. they are rare throughout this range, These are mostly individuals of surface their populations are declining quickly species showing no sign of adaptation (or under a threat of sharp decline), or to underground life. The exception is they are protected or listed as endan- Bangana musaei that has been observed gered by local, national or international only in caves around the upstream legal instruments (species that cannot entrance of the underground stretch of be fished; species whose trade is for- the Xe Bangfai, far upstream of the area bidden or limited [e.g. CITES], etc.); impacted by Nam Theun 2 activities - they have special evolutionary, scien- (Kottelat & Steiner, 2011). Another cave tific, emotional, or cultural importance fish (Troglocyclocheilus khammouan- (e.g. freshwater dolphin, giant Mekong ensis) is known from the resurgence of catfish). the Nam Done from the karst massive between the Nam Done (a tributary of 6.2 Biodiversity important species the Mekong) and Xe Bangfai drainages in Nam Theun 2 project area (on the road between Thakek and Mahaxai) (Kottelat & Bréhier, 1999). Most of the endemic species found Although the outlet is in the Nam Done in the Nam Theun 2 project area have The fishes of the Nam Theun and Xe Bangfai drainages, Laos 15 narrow ecological requirements. Most of them are specialised for habitats in fast water and they are found exclu- sively in these habitats. On Nakai Pla- teau, before inundation, most of these fast-water species were restricted to former rapids or were present only at a few specific sites. In the inundated zone, the species requiring rapids and fast water are now absent or have pop- ulations with fewer individuals. As their range upstream of the reservoir is not Fig. 2. Oryzias sp. 'swamp’, male (above) and inundated, a part of their habitat remains female (below); about 15 mm SL (photograph © and is protected by the NPA. In by Hiromichi Nemoto). repeated interviews in 1996, 2001, Fig. 2. Oryzias sp. 'swamp’, mâle (haut) et femelle (bas) ; environ 15 mm LS (photographie 2003 and 2007, villagers constantly © par Hiromichi Nemoto). answered that no species was known to be migrating or to have earlier migrated between the plateau and the upstream The survival of some midwater species Nam Theun and Nam Xot or to use the is also considered not to be an issue plateau as exclusive spawning and such as Devario fangfangae, Param- nursery ground. However, they become bassis sp. ‘slender’ (suspected new indirectly impacted, for example by species) and Oryzias pectoralis. increasing human population or human The present paper focuses on biodi- activity in the NPA (e.g. the introduction versity important species. of exotics and their pathogens). The species impacted by the inun- 6.2.1 Oryzias sp. 'swamp' dation only in part of their range and with strong populations upstream of Oryzias sp. 'swamp' (Fig. 2) is not the reservoir are classified as of lesser yet named following the rules of the biodiversity importance and do not International Code of Zoological Nomen- seem of priority concern (Tab. I). clature and the name Oryzias sp. Some species endemic to the Nam 'swamp' is used awaiting the publication Theun, Nam Gnouang and Xe Bangfai of the formal description and the 'official' drainages occur in habitats or areas name. It is known only from the Nakai where their survival does not seem to Plateau and its known distribution be an issue after impoundment (sug- range is almost totally inundated by gested by post-inundation surveys). Nakai Reservoir. These species are mainly small benthic The species was present in the sam- fishes. They are Schistura atra, Schistura ples collected as early as 1996 but was obeini, Schistura tubulinaris, Schistura not recognised. It was mixed with cataracta, Schistura nudidorsum, Oryzias sp. 'river', which then was mis- Nemacheilus arenicolus, Pterocryptis identified as Oryzias sinensis. Oryzias inusitata and Oreoglanis hypsiurus. sp. 'swamp' is distinguished from 16 M. Kottelat

Oryzias sp. 'river' by morphological the offsprings had already started to characters (especially in head shape, spawn, which corresponds to about 3 pigments on the head, maximum size, months. At hatching, the fry is about 4 number of anal-fin rays). Molecular data mm, which is smaller than known in all unambiguously show that it is distinct other species of the genus (K. Kubota, from Oryzias sp. 'river' and that both are pers. comm., 2012). Finally, these distinct from all known Oryzias species. observations suggest that Oryzias sp. Oryzias sp. 'swamp' is the smallest 'swamp' deposits the eggs on the sub- fish (and vertebrate) species known on strate or in crevices while in the other the plateau. The largest size observed species of Oryzias the female carries a is 20 mm SL although most specimens cluster of eggs for a few days hanging are below 18 mm SL. near the genital opening. Before inundation, Oryzias sp. Search for Oryzias sp. 'swamp' in 'swamp' was observed in the dry sea- 2009 and 2011 along the shores of the son in most pools, ponds and swamps Nakai Reservoir and in adjacent swamps on the Nakai Plateau (Kottelat, 2007), and wetlands failed to find the species where it was often present in large and it became of serious concern. The numbers. It survives the dry season in species was 'rediscovered' in 2012 at a shallow pools, with high temperature, single site. Investigations were con- low or no dissolved oxygen, and high ducted in the dry season 2013 by the organic pollution as these pools are Water Quality and Biodiversity depart- usually used by water buffaloes. The ment of the Nam Theun 2 Power Com- fish lives immediately under the water pany along the shores of the reservoir. surface, and its upturned mouth allows This survey included 68 swamps and it to breath in the very thin upper layer recorded the presence of Oryzias sp. of water in contact with air. 'swamp' at 8 sites. Most of the swamps However, these extreme habitats where the species was observed are were erroneously interpreted as spe- located below full supply level of the res- cialised habitat of the species. In fact ervoir (NTPC unpublished data; M. the sites where it was most abundant Cottet, pers. comm., 2014). had cooler water, with submerged veg- etation. In these habitats, the males are 6.2.2 Oryzias sp. 'river' 'colourful' with conspicuous red bands along the lower and upper edges of the Oryzias sp. 'river' (Fig. 3) too is not caudal fin. These sexually dimorphic yet formally named and is temporarily colour marks are totally indistinct in called Oryzias sp. 'river'. It is known murky water. only from the Nakai Plateau and its Little is known on the biology of the whole known distribution range is inun- species. Some aquarium observations dated by Nakai Reservoir. It was mis- indicate that individuals of about 12- identified as Oryzias sinensis in the 16 mm SL spawn 1 or 2 eggs per day earlier surveys. Before inundation, at during the warm-wet season (June– the end of the dry season the species September 2012). It seems that in early was collected only in the Nam Theun September, the oldest individuals of River, in low numbers, in backwaters or The fishes of the Nam Theun and Xe Bangfai drainages, Laos 17

Fig. 3. Oryzias sp. 'river’, adult female. Fig. 3. Oryzias sp. 'river’, femelle adulte. among shore vegetation. It seems that with the onset of the rainy season this Fig. 4. Scaphognathops theunensis, adult, 160 mm SL, collected in 1996 in Ban Thalang. species moved to the flooded areas Fig. 4. Scaphognathops theunensis, adulte, where it spawned. Other Oryzias spe- 160 mm LS, collecté en 1996 à Ban Thalang. cies of similar size reach sexual matu- rity in about 10-12 weeks, and several generations may succeed in a single Theun-Hinboun Reservoir and its annual cycle as observed in its relative extension reservoir. Information gath- Oryzias sp. 'swamp'. When the water ered in 2007 and 2009 indicated that the level decreases it survives in pools and species is present in the lowermost in the river. However, it seems that Nam Phao, a tributary of the Nam most individuals do not survive in pools Theun River entering it downstream of when the water level becomes too low, the Nakai Dam. Scaphognathops th- possibly because of high temperature eunensis could not be found down- and low water quality. stream of the confluence of the Nam In 2012, the species was present in Theun and Nam Gnouang (down- abundance all around the reservoir and stream known as Nam Kading). in backwaters and immediately below Research conducted in 2002 showed of the Nakai Dam. The species has that it is replaced by Scaphognathops apparently adapted very well to reser- bandanensis in the Nam Mouang, a trib- voir conditions and does not require utary of the Nam Kading. any management measure. The species lives in deep pools, usually immediately below riffles and 6.2.3 Scaphognathops theunensis rapids. Small juveniles had been col- lected in fast water at the future Nakai Scaphognathops theunensis (Fig. 4) Dam site in 1996. Apparently it feeds is endemic to the Nam Theun and Nam by scrapping algae growing on stones Gnouang main rivers. In the Nam Theun and logs, and the micro-invertebrates its range is totally included in the area living among the algae, with the narrow impacted by the Nam Theun 2 project. lower jaw terminated by a cornified In 2002 a survey was conducted in the sheath. Nam Gnouang to check its presence, Because of its habitat requirements distribution and habitat preferences and feeding habits, it was expected that (Kottelat, 2002). Since, the known dis- Scaphognathops theunensis would not tribution in the Nam Gnouang is totally survive in both the reservoir condition included in the area impacted by the (Nakai Reservoir and Nam Gnouang 18 M. Kottelat

Reservoir) and in the lower Nam Theun because of low post-inundation flow. With the 2002 survey’s condition, it was considered that it would survive only in the Nam Gnouang, if that river remained ecologically and hydrologically intact. Since that time, with the construction of the Theun-Hinboun extension on the Nam Gnouang, the survival chances of Fig. 5. Luciocyprinus striolatus; juvenile, 61 mm Scaphognathops theunensis are very SL (above) and subadult about 400 mm SL low in this area as well. (below). The presence of the species in the Fig. 5. Luciocyprinus striolatus ; juvénile, 61 mm lower Nam Phao was suggested by LS (haut) et subadulte, environ 400 mm LS interviews with local villagers in 2007 (bas). and 2009. With the poor habitat quality in the Nam Phao downstream of Lak- Nam Phao but not abundant, and was sao and the very poor condition of its also present in the Nam Theun upstream tributary Nam Kata (i.e. low flow, warm of the confluence with the Nam Phao. water, eutrophication, and severe local They considered the species now as mining pollution), a potential population 'not common'. Finally, individuals’ size in the Nam Phao cannot be considered was reported to be smaller than before safe and requires management meas- construction of Nakai Dam. ures to ensure its survival. In 2012, three individuals, about 100 mm SL, were observed in the 6.2.4 Luciocyprinus striolatus catch of fishermen in the Nam Theun downstream area. This observation Luciocyprinus striolatus (Fig. 5)is confirmed the presence of the species known from the Nam Theun and Nam and their size suggests that these indi- Gnouang drainages. Other populations vuals were about 2-3 years old, which are known in the upper Xe Kong, Nam implies that they were born in 2009- Ngiep and Nam Ou in Laos, and in 2010, that is after completion of Nakai Xishuangbanna in Yunnan (China). In all Dam. This leads to suggest that the these areas it is rarely observed and the species had been able to survive (at only rivers where it has been regularly least temporarily) the low flow condi- seen are the Nam Gnouang and upper tions. However, the parents were born Nam Theun. It is not present in the probably 3-4 years before, which was Mekong main river or in the lower parts before completion of Nakai Dam. of its main tributaries. As most of the Future will show whether the individu- upper parts of the other main tributaries als born after closure of the dam will be of the Mekong in Laos have not yet been able to reach maturity and spawn. surveyed (or the results have not been Villagers in the Nam Theun down- made public), its presence in some stream of the Nakai dam reported that additional drainages cannot be excluded. the species was present in the lower In any case its range is very fragmented. The fishes of the Nam Theun and Xe Bangfai drainages, Laos 19

Also, it cannot yet be excluded that some of these isolated populations in fact are different species. Luciocyprinus striolatus inhabits large deep pools. Its habitat on the Nakai Plateau has been lost by inunda- tion and it is unlikely to maintain a sig- nificant population in the Nam Theun downstream of Nakai Dam. Its only known intact habitats are the small stretches of the Nam Xot and upper Fig. 6. Tor ater; juvenile, 180 mm SL (above) Nam Theun. If the species does not and adult, 460 mm SL(below). migrate and does not need to travel Fig. 6. Tor ater ; juvénile, 180 mm LS (haut) et adulte, 460 mm LS (bas). long distance to feed, it will apparently survive in the deep pools above FSL. Because it is a very large fish (up to that overfishing is responsible for the at least 1.5 m, with villagers mentioning absence of larger individuals. sizes above 2 m), the number of indi- viduals is predictably very low and 6.2.5 Tor ater overfishing is an immediate threat. It is most likely already overfished, even if Tor ater (Fig. 6) is definitively not the object of a specific fishing activ- recorded only from the Nam Xot and ity. In recent years, it also attracted Nam Theun upstream of Nakai reser- attention as a target for sport fishing. voir. Although originally described Villagers from both above the reservoir (Roberts, 1999) on the basis of speci- and downstream of Nakai Dam inter- mens obtained from villagers in Ban viewed during the surveys 1996, 2001 Thalang there is no indication of its ear- and 2003 surveys all commented that lier presence on Nakai Plateau. A sur- the species is not migratory and vey conducted in 2002 in the Nam spawns in January-February in rapids Gnouang and Xe Bangfai drainages to (Kottelat, 1996, 2002). investigate its possible presence out- In 2012, L. striolatus was observed side the Nam Theun drainage failed to in the Nam Theun both upstream and find it (Kottelat, 2002). Its distribution downstream of the Nakai Reservoir. It and biology in the Nam Theun drainage is not known in the Nam Phao. In the was investigated in 2003 (Kottelat, upstream Nam Theun, four individuals 2004). Villagers do not report having about 50-60 mm SL were observed at seen the species on the plateau and as the uppermost extremity of a pool, far as known it completes it whole life immediately downstream of the rapids/ cycle upstream of the plateau, as sug- riffles. Villagers reported that they are gested by the presence of individuals of no longer observing large individuals three age classes. and that those they now collect are not Adult Tor ater seem to inhabit deep more than 30 cm long. They consider pools and to spawn in riffles. 20 M. Kottelat

Species of the genus Devario often have a large range and are frequent within their range. For example, Devario fangfangae, which is endemic to the Nam Theun and Nam Gnouang drain- Fig. 7. Devario sp. 'green', 47 mm SL. ages, is mainly a species of forest Fig. 7. Devario sp. 'green', 47 mm LS. streams, but it is also regularly seen in other habitats, and has also been The smallest known individuals 104- observed in the reservoir. Other spe- 140 mm SL had been obtained in a cies, on the reverse, may have very small creek. restricted ranges. Devario sp. 'green' The species was not observed by was collected in a forest stream habitat, the 2012 survey and no information with little water, and probably has the were obtained. The site where juve- same ecological requirements. It was niles had been obtained in 2003 was expected that the species would be visited in 2012 but a small village has present elsewhere in the Nam Kathang been established and sampling was or in the Xe Bangfai drainages. The not possible at this exact site. baseline survey conducted in 1996 and The only information available on 2006 did not show its presence in the Xe this species were obtained by the 2003 Bangfai drainage, but the focus then survey (Kottelat, 2004) and are very lim- was on the Xe Bangfai main river. Hab- ited. Study is needed to determine its itats similar to the upper Nam Kathang distribution, ecological requirements, Gnai were not sampled at that time reproductionpattern,andpopulationsize. because none could be accessed. Attempts to find Devario sp. 'green' 6.2.6 Devario sp. 'green' outside the Nam Theun 2 project area failed. The only other Devario species This species (Fig. 7) had been col- observed in the Xe Bangfai drainage lected only in the Nam Kathang Gnai, a during the surveys was in the Nam branch of the Nam Kathang on Nakai Oula catchment; it is a conspicuously Plateau during the 2007 and 2012 sur- distinct species, possibly new to sci- veys. It is new to science and presently ence. Adjacent areas in Vietnam are known only from this stream. The spe- inhabited by Devario quangbinhensis, cies is not affected by the inundation of a species somewhat similar to the Nam the reservoir since this stream flows Oula one. Anyway, the endemism of directly to the Xe Bangfai, not to the Devario sp. 'green' to Nam Theun 2 Nam Theun. However, some resettled project area should be confirmed by villages are located on and across the search for possible additional popula- divide between the Nam Theun and tions outside the Nakai Plateau. The Nam Kathang Gnai, and other villages presence of a second species of the are very close to the divide. Then, the genus in the Nam Oula suggests that main expected disturbance of its habi- the distribution of Devario sp. 'green' tat may be related to the disturbance by might not be very wide since there is no villages (e.g. agricultural activities). known instance in Southeast Asia of The fishes of the Nam Theun and Xe Bangfai drainages, Laos 21

Bangana elegans inhabits rapids and fast flowing waters, and spawns at rapids. It disappeared from the Nakai Plateau after inundation of the reser- voir. It is expected to become rare or disappear in the downstream Nam Fig. 8. Bangana elegans: juvenile, 133 mm SL. Theun. It has been observed in the Fig. 8. Bangana elegans : juvénile, 133 mm LS. Upper Nam Theun, the Nam Xot, and Nam Noy and individuals from about 2 to 30 cm had been observed, in the two species of Devario occurring earlier surveys, suggesting that it com- together. Alternatively, this might sug- pletes it whole life cycle in these gest that the two species have different stretches of the rivers. In 1996 villagers ecological niches. in Ban Thalang reported that Bangana If Devario sp. 'green' were to turn elegans undertakes small local migra- out to be restricted to Nakai Plateau, tions to spawn in rapids in November, then management measures should while people at Nakai Dam site include e.g. forest cover conservation reported its presence year round. It along the stream, prohibit water spawns on shallow rocks (reportedly abstraction to ensure a constant flow, less than 10 cm deep). Spawning in even low, during the dry season. shallow water means that the eggs and early larvae would not survive a 6.2.7 Bangana elegans decrease of water level during the few days between spawning and the time Bangana elegans (Fig. 8) is pres- the larvae can move away. The time ently known only from the Nam Kading needed is not known but can be drainage (Nam Theun and Nam expected to be 1-2 weeks. Further, vil- Gnouang Rivers). An earlier tentative lagers used to catch this species with record from Nam Ngum was based on trident in the rapids during spawning. a juvenile that could not be identified With less water and shallower rapids, with accuracy (Kottelat, 2001). Adult this fish becomes an easier target. Bangana recently collected in the Nam Since impoundment of the Nakai Res- Ngum and Nam Ngiep have been iden- ervoir, the species has never been tified as Bangana lippa. There is no seen in the inundation zone, except in data available for intermediate areas. the parts of Nam Noy (M. Cottet, pers. The presence of a Bangana species is comm., 2014), Nam Theun and Nam expected in headwaters of most rivers Xot, where these rivers are under FSL. north of the Nam Gnouang. Bangana elegans could be present in the drain- ages immediately north of the Nam 6.2.8 Rhodeus laoensis Gnouang, at least in the Nam Kading drainage. There is no record of Ban- Rhodeus laoensis (Fig. 9) is endemic gana species south of the Nam Theun to the Nam Theun and Nam Gnouang drainage. drainages. In the Nam Theun, before 22 M. Kottelat

Rhodeus laoensis is a bitterling, a group of fishes that spawn their eggs in mussels, where they hatch and remain for 1 to 8 months. The length of the stay in the mussel depends on the bitterling species. There is no data for Rhodeus laoensis but the small size of the free- swimming juveniles suggests it is among the species spending only a short time in the mussel. Bitterlings can- not complete their life cycle without the mussel and their survival is therefore absolutely dependant of the presence of the mussel. Each species of bitterling Fig. 9. Rhodeus laoensis; male, about 40 mm needs the presence of one (or a few) SL (above) and female, about 40 mm SL with black ovipositor tube (below). precise species of mussel (e.g. Liu Fig. 9. Rhodeus laoensis ; mâle, d’environ 40 mm et al., 2006; Kitamura, 2007), and if that LS (haut) et femelle, d’environ 40 mm LS avec species is not present it will not use un tube ovipositeur noir (bas). other species. While the fish may move for some distance if habitat conditions become unfavourable, the adult mussel inundation it had been observed mainly cannot move. If the stream bed on the Nakai Plateau and in small trib- becomes exposed, polluted, silted or utaries of the Nam Theun upstream. On anoxic the mussel dies and this may the plateau (inundation zone) it was lead to the local extirpation of the fish. found only in the main river and in forest The mussel has a larval stage, streams and has never been observed called glochidia. The larvae are para- in the swamps. This species was sitic and attach to the gills and fins of extremely frequent, and during the fishes until they metamorphose, then 2001, 2006 and 2007 surveys very they drop to the bottom. This means small juveniles were abundant. It pre- that the mussel has the potential to be fers sections of forest streams with slow carried by fishes in new habitats or to or standing water with submerged veg- be carried back to habitats from which etation and soft bottom, often close to they had been extirpated. As they need deeper water. If the habitat becomes to be permanently in water, of course disturbed by human activity and the cur- they would be unable to establish in the rent becomes slower and the water drawdown zone. The time needed for slightly turbid, it replaces the typical metamorphosis varies depending on species of this habitat (especially species, and there is no data for the Devario fangfangae and Rasbora pavi- mussel of the Nam Theun drainage. ana), which become less abundant. Depending on the species, glochidia This species was also observed down- may need one or a few precise fish stream of the Nakai Dam area in the species to attach, or may be more gen- Nam Phao in 2007. eralistic and attach to many different The fishes of the Nam Theun and Xe Bangfai drainages, Laos 23

Rhodeus laoensis had not been observed in the inundation zone after 2007. After the impoundment, specimens were observed from villagers in the Nam Theun downstream of the Nakai Dam (M. Cottet, pers. comm., 2014). It has been observed in 2012 in the Nam Theun upstream of the reservoir. In the Nam Theun drainage, the mussel Pseudodon vondembuschi- anus was observed in 2009 and 2012 in the Nam Phiat, a small tributary of Fig. 10. Pseudodon vondembuschianus, the the Nam Phao. The presence of live only species of mussel observed in Nam Theun mussels in a habitat should not be drainage, in which Rhodeus laoensis probably taken as meaning that the mussel is deposits its eggs. safe. Many species of Unionidae can Fig. 10. Pseudodon vondembuschianus,la seule espèce de moule observée dans le bas- live very old (one species up to sin de la Nam Theun, dans laquelle Rhodeus 120 years) and some species still have laoensis dépose probablement ses œufs. surviving individuals but they are func- tionally extinct because they only sub- sist as a few localised populations fish species. If the glochidia need to made only of old individuals no longer attach to a precise fish host (other than reproducing, or the number of individu- the bitterling), then the survival of both als is too low to support a viable popu- the mussel and the bitterling depend of lation (Bogan, 1993). A bitterling depend- the survival of this host. ing of a functionally extinct species of The mussel host Rhodeus laoensis mussel would be condemned to extinc- is not yet objectively known, but a single tion unless an alternative host can be species has been collected in the Nam found. A number of species of mussels Theun drainage. It belongs to the family have disappeared following the con- Unionidae, as all species used by bit- struction of dams in North America terlings. It has been identified as Pseu- (Bogan, 1993, 2006; Watters, 2000). dodon vondembuschianus (Fig. 10, Many species of bitterlings suc- identification by A. Bogan). The popu- cessfully breed in captivity (Akai et al., lation from Laos had been identified by 2005) and the conservation program of Brandt (1974) as a subspecies P. v. at least one species in Korea is based tumidus. The distribution of Pseudodon on captive breeding. Captive breeding vondembuschianus includes mainland has always been in presence of the Southeast Asia, Sumatra, Java and mussel. Borneo. Some authors consider that Pseudodon vondembuschianus or a populations from the Mekong drainage very similar species of mussel was col- in Laos and Cambodia are a species lected in the Ban Done drainage, where distinct from those from Indonesia, but it was common. The identity of this sam- this is still debated. ple has not yet been confirmed. The 24 M. Kottelat

Fig. 12. The second species of Pangio aff. Fig. 11. Pangio aff. fusca,33mmSL. fusca, from the Xe Bangfai drainage. Fig. 11. Pangio aff. fusca,33mmLS. Fig. 12. La seconde espèce de Pangio aff. fusca, du bassin de la Xe Bangfai. presence of a population of this species near Nakai Plateau is important as it to the Salween drainage and Tenas- might be a source of material usable for serim (Myanmar) and that the popula- captive breeding of Rhodeus laoensis tions from the Mekong drainage belong or for research. Other species of mus- to other species (Britz & Maclaine, sels were also collected in the Xe 2007; Britz & Kottelat, 2010). Further, in Bangfai drainage. earlier reports (Kottelat, 2006, 2007), Because the presence of the mus- all the Pangio fusca-like fishes of the sel is necessary to allow the complete Mekong drainage were believed to be a life cycle of Rhodeus laoensis, man- single species, although there was a agement measures should focus on suspicion that more than one species both the fish and the mussel (Kottelat, were confused under this name (Kotte- 2012b). It is necessary to confirm that lat, 2007). This is now confirmed by a Pseudodon vondembuschianus is the recent and still unpublished study that species used by Rhodeus laoensis and distinguishes three species, diagnosed that Rhodeus laoensis is the species by morphological as well as molecular used by the glochidia of this mussel. characters. One of them is known only Should there be more than one species from the Nam Theun drainage (called of mussel, there would be the risk of here Pangio aff. fusca). Another similar targeting conservation measures at the species has been observed in the Xe wrong species. This requires either Bangfai by the 2012 survey (Fig. 12). direct observation of spawning or The species is very elusive and only searching for eggs or fish larvae in the 12 individuals have been observed, all mussels. It is also necessary to estab- in 1996. All individuals were observed lish which fish species is/are used by in localities in the inundation zone, with the glochidia (the larvae of the mussel). soft bottom and/or leave litter, a normal habitat for species of the genus Pangio. 6.2.9 Pangio aff. fusca It was also collected at the Nakai Dam site in 1996 and therefore expected for Pangio aff. fusca (Fig. 11) was ear- at least some distance in the Nam lier identified as Pangio fusca, a spe- Theun downstream. Some individuals cies then believed to be widely distrib- have a very dark colouration and this uted from the Salween to the Mekong suggests that it possibly also inhabits drainages. Later studies have shown crevices in rocks, as at the dam site. In that Pangio fusca is actually restricted such habitats they can be very difficult The fishes of the Nam Theun and Xe Bangfai drainages, Laos 25

edge of the plateau but is not a tributary of the Nam Theun. Instead, it flows down the escarpment to the Xe Bangfai. It cannot be identified with any of the species known in the Nam Theun and Xe Bangfai drainages and is new to sci- ence and named Schistura sp. 'Nam Kathang' until given a formal name. This species is not affected by the inundation Fig. 13. Schistura sp. 'Nam Kathang'; juvenile, of the reservoir, but the new Ban 22 mm SL (above) and adult 59 mm SL (below). Khonken village is located on and Fig. 13. Schistura sp. 'Nam Kathang' ; juvénile, 22 mm LS (haut) et adulte 59 mm LS (bas). across the divide between the Nam Theun and Nam Kathang Gnai, and other villages are very close to the to collect. The largest number of indi- divide, so that disturbance of its habitat viduals in a single sample (5) was from by villages is to be expected. a small forest stream near (old) Sop On Species of the genus Schistura village, in the inundation zone with soft often have small distribution ranges, bottom. It is expected to be present in often limited to a single river drainage small, permanent tributaries, with a low or subdrainage. For example most gradient. species present in the Nam Theun and There is a number of small forest Nam Gnouang are endemic to these creeks entering the Nam Theun between rivers. However, it is not expected that the Nakai Dam and the confluence with this species would be restricted to the the Nam Phao that could home this spe- Nam Kathang Gnai but that it is proba- cies. On Nakai Plateau, the Nam On, bly present elsewhere in the Xe Bang- which is inundated only for a short fai drainage, probably together with period every year, could also present Devario sp. 'green'. suitable habitats for this species. Schistura sp. 'Nam Kathang' was Because of its habitat and life habit, observed at two sites in the Nam the absence of the species in surveys Kathang Gnai, accessed from Ban is not conclusive and suggests that the Khonken area, where the stream was preferred habitat is missed by the sam- very narrow and shallow, under forest pling methods. Most species of this cover, with a muddy to sand substrate, genus burrow in sand or mud and may and Ban Done area where the stream escape ichthyocides if they are washed had been forded, resulting in a deep too quickly by the current. pool upstream, very slow current and algae development on the bottom. 6.2.10 Schistura sp. 'Nam Kathang' There, the species was collected in the riffles at the level of the ford, which is the Schistura sp. 'Nam Kathang' (Fig. 13) habitat of most species of Schistura. has been observed only in the Nam Devario sp. 'green' and Schistura Kathang Gnai on Nakai Plateau. The sp. 'Nam Kathang' are both known only Nam Kathang Gnai is flowing along the from the Nam Kathang Gnai and 26 M. Kottelat

Fig. 14. Microcobitis aff. misgurnoides, 31 mm SL. Fig. 15. Devario aff. quangbinhensis,75mmSL. Fig. 14. Microcobitis aff. misgurnoides,31mmLS. Fig. 15. Devario aff. quangbinhensis,75mmLS. attempts to find them outside the NTPC This unpleasant habitat probably area failed. As the species seem to be explains why it had been overlooked. impacted by resettlement activities, fur- However, it is not restricted to this hab- ther studies are needed to determine itat and was also collected in the Nam their endemism. They should include Theun and Nam On rivers at places the search for possible additional pop- with sand to muddy bottom. In the field ulations outside the Nakai Plateau. it is easily confused with Lepidocephal- ichthys hasselti with which it co-occurs 6.2.11 Microcobitis aff. misgurnoides at all localities, in the same habitat. Microcobitis aff. misgurnoides is Microcobitis aff. misgurnoides now present in large numbers in sites (Fig. 14) was first discovered during the in the inundation zone and is abundant 2007 survey. It is a still unnamed spe- in the mud bottom of pools connected cies related to Microcobitis misgur- with the reservoir at FSL. noides, a species known only from Cen- tral Vietnam (Rendahl, 1944; Bohlen & 6.2.12 Devario aff. quangbinhensis Harant, 2011). Morphology and molecu- lar data show that they are distinct spe- While searching for Devario sp. cies. 'green' in the Xe Bangfai drainage, Before inundation, Microcobitis aff. another species of Devario was col- misgurnoides had been observed lected in the Nam Oula catchment mostly in shallow lakes on the Nakai (Fig. 15). This species cannot be iden- Plateau. A few individuals were found tified with any of the species known in in the Nam Theun and the Nam On, in the Mekong drainage. It is possibly new the inundation zone. It has never been to science and has an appearance sim- observed further upriver. In 2007, it has ilar to that of Devario quangbinhensis, also been observed in a drying river a species described from Vietnam in the northeast of Laksao, which indicates drainage of River Chay, in Quang Binh that the species is not endemic to the Province, which is adjacent to the Xe Nakai Plateau. Bangfai drainage. The species was It is a benthic species, living in soft obtained in a small creek in the forest bottom. Most individuals were obtained upstream of the limit of that stretch of the in samples that contained Oryzias spe- Nam Oula impacted by the increased cies and Esomus metallicus, species flow and level in the Xe Bangfai. that survive the dry season in the worst However, further surveys are needed conditions in dry pools and swamps. to determine its endemism. This includes The fishes of the Nam Theun and Xe Bangfai drainages, Laos 27

Fig. 17. Oreoganis lepturus,53mmSL. Fig. 17. Oreoganis lepturus,53mmLS.

Fig. 16. Parambassis sp. 'slender', 43 mm SL. Fig. 16. Parambassis sp. 'slender', 43 mm LS. 6.2.14 Oreoglanis lepturus

Oreoglanis lepturus (Fig. 17) is only the search for possible additional pop- known from the Nam Phao and might ulations in the Xe Bangfai drainage and be present in the upstream Nam possibly in the Xe Banghiang. Gnouang. In the Nam Phao it has been observed in 1996 and 2006 only in the 1-2 km immediately downstream of the 6.2.13 Parambassis sp. 'slender' border between Laos and Vietnam, in a stretch with stones and boulders and The Parambassis (Fig. 16) species small waterfalls, and in 2012 in the observed in the Nam Theun and Nam Nam Kata, in drying riffles. Gnouang drainages has similarities Both sites are in sectors very with Parambassis siamensis. However, impacted by human activity (e.g. irriga- it is possibly a distinct species because tion network, road construction, gold of its more elongated body. mining, and fishing). However, the areas This species was first observed in where the species was observed are the Nang Gnouang in 2002 and in the not under the direct influence of the Nam Phao in 2007. It was not present Nam Theun 2 project. in the samples obtained between 1996 and 2009 immediately upstream of 6.2.15 Rhinogobius lineatus Keng Louang but it was very abundant in 2012 immediately downstream, where Rhinogobius lineatus (Fig. 18)is several hundreds were seen. Species definitively known only from the Nam of Parambassis elsewhere inhabit rela- Theun downstream of the Nakai Dam tively slow and standing waters and the and the Nam Gnouang. It was observed decreased flow in the Nam Theun and in 1996, 2002 and 2009. standing water in Theun Hinboun res- The complete range of the species ervoir are likely to create more suitable is impacted by Nam Theun 2 and Theun environment for this species. Even if its Hinboun activities. Most of the sites on endemic status is not yet confirmed it the Nam Gnouang are now inundated seems that no management measure is by Theun Hinboun extension dam. On needed for this species other than a rou- the Nam Theun, it was present in 2009 tine presence monitoring should be downstream (Keng Louang, Keng Iru) undergone in the Nam Theun River after completion of the Nakai Dam but downstream. was not seen in 2012. 28 M. Kottelat

and 2012; several sites were visited twice and one site was visited 3 times. In 2012, the situation of the aquatic habitats in the upstream Nam Theun above FSL has not changed signifi- cantly since the original 1996 survey. However the human population has increased and is more present along the river, with more houses and new Fig. 18. Rhinogobius lineatus; male, 36 mm SL hamlets. The river morphology does (above) and female, 37 mm SL (below). Fig. 18. Rhinogobius lineatus ; mâle, 36 mm LS not seem to have changed although at (haut) et femelle, 37 mm LS (bas). least one site that earlier was a sand bank had become a bar of boulders, The genus Rhinogobius was col- which seems a natural process, possi- lected only once in the Xe Bangfai in bly the result of the 2011 storms. 2002, close to the downstream entrance No difference in the number of spe- of the underground course of the river. cies and the composition of the fish Unfortunately this individual was a female communities was observed. This was and the characters useful to identify spe- expected since this stretch of the river cies of Rhinogobius are mainly found in is entirely within the NPA. However, the males. This female cannot be reliably number of fish individuals seems lower identified, but it shows similarities with and the size of the fishes seems the females of Rhinogobius lineatus. smaller, suggesting overfishing. Survey should be conducted to The species diversity at the upper- obtain more material of the Xe Bangfai most point that can be reached by boat putative population and clarify whether was comparable to that of previous or not it is Rhinogobius lineatus.It years: 23 species collected in 2012, 18 should also be searched in the subsist- in 2006, 26 in 2003. But compared to ing small streams entering the Nam earlier years, there was no large fish in Gnouang and downstream Nam Theun. 2012. Although no conclusion can be Its continued presence in Keng Iru and reached from a single sampling, this Keng Louang where it was seen in 2009 might reflect an increased fishing pres- should be monitored. It is probably also sure. It might as well reflect that at this present in the Nam Kading and its trib- site the water was shallower and flow- utary streams. ing over a much wider bed while in the previous years the rapids were nar- 7 MODIFICATION OF FISH rower and deeper. Increased fishing COMMUNITIES IN THE NAM THEUN pressure was also reported to be the 2 PROJECT AREA cause of the rarefaction of large individ- uals of Luciocyprinus striolatus. 7.1 Upper Nam Theun 7.2 Nakai Plateau Sampling was conducted in the The Nakai Plateau being now upper Nam Theun in 1996, 2003, 2006 almost totally inundated part of the The fishes of the Nam Theun and Xe Bangfai drainages, Laos 29 year, the riverine species, and espe- samples included 10 to 16 species, cially the rheophilic ones, have disap- while the 2012 sample includes 23 spe- peared. The species inhabiting the cies. swamps are still present. Two are very Five of the species observed in 2012 abundant (Oryzias sp. 'river', Microco- and absent in the samples of the previ- bitis aff. misgurnoides). A third one ous years prefer slow flowing or even (Oryzias sp. 'swamp') was present in standing water (Cyclocheilichthys arma- large numbers before inundation but is tus, Esomus metallicus, Nemacheilus now rare and localised. arenicolus, Parambassis sp. 'slender', Puntius brevis). Three species present in 2012 but not recorded earlier are spe- 7.3 Lower Nam Theun cialist of fast waters (Garra cyrano, Balitoropsis yunnanensis, Schistura The closing of Nakai Dam resulted atra). A single species was present in all in a very reduced flow most of the year five samples (Poropuntius carinatus). (2 m3/s), and without variation. Parts of Opsarius pulchellus was present in all the rapids are now exposed, sand previous samples but missing in 2012. banks have become more extensive, In the 2009 sample, 4 out of 14 spe- etc. The species most specialised for cies also had not been observed before rheophilic habitats become rarer and and they were also species not usually some are expected to disappear. associated with rapids (Devario fang- Native species requiring slower water fangae, Hemiculterella macrolepis, Neo- (e.g. Parambassis sp. 'slender') or dontobutis aurarmus, Rasbora paviana). sandy bottoms (e.g. Nemacheilus are- In 2009, two species typical of rapids nicolus) become more abundant. and observed in all previous samples The Keng Louang rapids on the were missing (Garra theunensis, lower Nam Theun were sampled in Scaphiodonichthys acanthopterus). 1996, 2006, 2007, 2009 and 2012. The A variation in the presence/absence first four samples were obtained at or abundance of a species is normal exactly the same location. In 2012, the and expected. The differences between water level was so low that the river the samples, however, is partly explained could be crossed in stepping from by the different location and different stone to stone; the earlier sampling site morphology of the sampling sites. The was exposed and another site had to 2012 downstream site included a pool be selected, not totally equivalent. with little current at the time of the visit. Table III shows the species collected at Apparently this also confirms a shift Keng Louang in 1996, 2006 and 2007 towards a less rheophilic fish community before closure of the dam, and 2009 already observed in 2009 after the clo- and 2012 after closure. The 2006 sam- sure of the Nakai Dam and the lower ple is indicative only; the identifications and extended dry season release. were based on field observations (the There is also indication that species courier company destroyed the sample). from very slow or standing water of The list of species shows great varia- Theun-Hinboun reservoir may now be tion between the years. The 1996-2009 able to invade the lower Nam Theun. It 30 M. Kottelat

Table III. Fish species collected in downstream Nam Theun at Keng Louang rapids between 1996 and 2012. Note: identifications for sample 2006 are based on field notes and the list is probably incomplete (see text). Samples from 1996 to 2009 were obtained at the same location at the upper edge of the rapids; in 2012 this point was emerged and the sample was obtained at mid height of the rapids. Tableau III. Espèces de poissons de poissons récoltées dans la Nam Theun inférieure, aux rapides de Keng Louang entre 1996 et 2012. Note : les identifications de l'échantillonnage de 2006 sont basées sur les notes de terrain et sont probablement incomplètes (voir texte). Les échantillons de 1996 à 2009 ont été obtenus au même emplacement au bord supérieur des rapides ; en 2012 cet emplacement était émergé et l'échantillon a été obtenu à mi-hauteur des rapides. Species 1996 2006 2007 2009 2012 Balitora lancangjiangensis xx Balitoropsis yunnanensis x Cirrhinus molitorella x Cycloceilichthys armatus x Devario fangfangae x Esomus metallicus x Garra cambodgiensis xxxx Garra cyrano x Garra theunensis xxx x Glyptothorax laosensis xx Glyptothorax horai xx Glyptothorax aff. zanaensis xxx Gyrinocheilus aymonieri xxx Hampala macrolepidota x Heminagrus wyckioides xx Hemiculterella macrolepis x Hemimyzon papilio x Homalopteroides smithi xx x Mastacembelus armatus xx Mystacoleucus marginatus xx Nemacheilus arenicolus x Neodontobutis aurarmus x Onychostoma fusiforme x Opsarius pulchellus xxxx Papuligobius ocellatus xxx x Parambassis sp.'slender' x Poropuntius carinatus xxxxx Puntius brevis x Rasbora paviana xx Rhinogobius lineatus x Scaphiodonichthys acanthopterus xxx x Schistura atra x Schistura cataracta xxxx Schistura kongphengi xx Schistura obeini x Tor tambra xx Total 10 10 16 14 23 The fishes of the Nam Theun and Xe Bangfai drainages, Laos 31 also cannot be excluded that some of much more difficult because of the these species were not native but intro- higher water level and greater dis- duced in Theun Hinboun Reservoir. charge. Effective sampling in the river itself is possible only with the local seines and local population. In 2012, 7.4 Nam Phao suitable conditions were present in Ban Boungxe, a site already sampled in The Nam Phao (and its branch Nam 2006. Kata) is the only tributary of the Nam In 2012, 28 fish species were Theun downstream of Nakai Dam. It obtained in water less than about 2 was expected that these rivers could meters deep, by seine over sandy bot- serve as refuges for juvenile and small- tom. This compares with 25 species sized species. Unfortunately, these obtained in 2006 in the same area. In tributaries suffer great anthropogenic the same area, the 1996 sampling had impacts. Some have been observed yielded 40 species near the confluence since the beginning of the monitoring in with the Mekong and 38 on a 7-km 1996 (e.g. the formation of large sand stretch downstream of the bridge at banks and filling of all deep holes of the Ban Khouaxe. The combined total Nam Phao, a result of the construction number of species of these two sam- of a small dam upstream of Laksao and ples was 57. The number of species of road work). The number of species was considerably higher but the 1996 obtained by the 2012 survey and the samples involved more workers, longer number and size of the individuals seines (200 m vs. 50 m), lasted a whole seems lower. The number of samples day each, and included various habi- is probably too low to reach an objec- tats (mud, clay, sand, gravel bar, back- tive conclusion. waters etc.) while only sand was avail- The situation of the Nam Kata did not able at the site sampled in 2012. differ between 2002 and 2012 in the vis- Nine species out of 28 (32%) ited stretch. The Nam Kata suffers of obtained at the 2012 site had not been strong sedimentation and is heavily observed in the same area by the 1996 impacted by mining and the related pol- and 2006. Among them, 4 species had lution, water abstraction, eutrophica- not been recorded in the Xe Bangfai tion, and possibly pesticides. At each before, and one (Acantopsis sp. 'dwarf visit, the fish densities were low and the males') is possibly new to science. fish collected were all juveniles or are That a single sample in 2012 small-sized species. included 1/3 of species not observed before in that part of the river with a similar methodology indicates that the 7.5 Downstream Xe Bangfai fish fauna of the lower part of the river is still undersampled, that more sam- The modified water conditions make pling should be conducted. In fact the it impossible to replicate the sampling various surveys have taken only 7 done in 1996 and 2006. In addition sam- samples in the Xe Bangfai itself down- pling in the Xe Bangfai itself is now stream of the bridge (Ban Khouaxe) 32 M. Kottelat between 1996 and 2012. It is also were included in the surveys. On the expected that sampling at the same reverse, the coverage for the upper part site at different times of the year would of the Xe Bangfai is very limited and the yield different species. Sampling by sampling on the whole river was less night would also add a number of spe- dense than on the Nam Theun. cies, especially catfishes. Despite these reservations, our sur- No conclusion on the impact of veys show that the Nam Theun has NTPC activity on the fish diversity of fewer species than the Xe Bangfai but that stretch of the Xe Bangfai can be that 21 (28%) of the 74 native species derived from this sampling. are endemic. It might be that some of Two samples were obtained in the these species await to be discovered in Xe Noy, a main tributary of the Xe Bang- other tributaries of Nam Kading and in fai, at and above the maximum extent of the Nam Xan drainage north of the the water backed up by the increased Nam Theun. Besides, as mentioned flow of the Xe Bangfai. A combined total above, a number of species of the Nam of 48 species was obtained. The Theun are closely related with species observed fish community is represent- and genera otherwise known only from ative of what was known in the Xe Bang- the other side of the Annamite Range fai in similar habitats between Mahaxai and unknown or with very restricted and the confluence with the Nam Phit. ranges in the Mekong drainage. The fauna of the Nam Theun has more sim- ilarities with that of the drainages to the 8 DISCUSSION – CONCLUSION north. On the other hand, only 9 (5%) of 8.1 Fish biodiversity the 178 species reported from the Xe Bangfai are endemic. The Xe Bangfai Detailed surveys before construc- fish fauna is similar to the fauna of the tion allowed to identify the biodiversity Mekong major tributaries to the South, important species and to focus atten- in Laos and Thailand. Three of the tion on them during monitoring. 'endemics' were discovered by the The fish fauna of the Nam Theun 2012 survey in habitats still insuffi- and the Xe Bangfai are strikingly differ- ciently sampled in other drainages and ent. There is an obvious difference in some are expected to be discovered richness, with 74 native species in the there too. Nam Theun drainage and 178 in the Xe The majority of the Nam Theun fish Bangfai drainage. Part of the difference species inhabit rapids and very fast results from the different purposes of waters (rheophilic habitats), with some the various samplings, which imposed (Oreoglanis spp., Pseudecheneis sym- priorities and geographical limits: while pelvica) present even in waterfalls. the Xe Bangfai was surveyed for its Many of these species have developed whole length, from the headwaters to structures that allow them to keep posi- the Mekong, the Nam Theun is only the tion in strong current, like laterally upper part of the Nam Kading drainage expanded fins, fins fused to form a and no lowland and floodplain habitats sucker, sucking mouth, gill opening The fishes of the Nam Theun and Xe Bangfai drainages, Laos 33 modification allowing to inhale and distribution within a drainage, but also exhale water, tubercles on the snout to because the ranges of rheophilic spe- reduce the pressure of the current, cies are restricted to a few or a single jaws with a sharp cutting edge to drainage. Because of its morphology, scrape algae from the surface of the the Nam Theun has a fauna mostly rhe- stones, skin lamellae on the belly with ophilic (38 out of 74 species), of which a structure similar to the sucking disk of 13 (34%) are endemic (or endemic to remoras, etc. The Xe Bangfai has very the Nam Theun + Nam Gnouang). In few species with such structures (but other words, 1/6 of the fish species of this may partly reflect that suitable hab- the Nam Theun were potentially threat- itats could not be reached). ened of extinction by the project. To date, a single species of the Xe The rivers upstream of the Nakai Bangfai is also known, or is closely Reservoir are large and diverse enough related to a species, from the other to provide habitats to all but two of the slope of the Annamite Range in Vietnam endemic rheophilic species. These (Devario aff. quangbinhensis), although habitats are within the NPA and there- the divide between the two slopes is fore supposedly safe at the short and very low (about 400 masl). medium term. Since no long-distance The swamp and marsh habitats of migratory species was found (and none the Nam Theun and Xe Bangfai drain- was reported by the local population) ages also differ conspicuously. The the dam is not a barrier threatening the swamp habitats of the Xe Bangfai are life cycle of any migratory species. Fur- in the Mekong floodplain and have a ther, downstream of Nakai Reservoir, rich fauna, made mostly of species the river was already blocked by Theun- present throughout the floodplain of the Hinboun Dam. middle Mekong, with no endemic. On The future of one rheophilic species the other hand, the swamp habitats in not observed upstream of the reservoir the Nam Theun are located on Nakai (Scaphognathops theunensis) is dim- Plateau. They are fed by rain and by mer. At the time the surveys were con- the cool water of the Nam Theun. They ducted, a significant share of its range have a very small number of species was in the Nam Gnouang and it but three of them are endemic, and two seemed to be reasonably safe. How- only known from the inundation zone. ever, between the time the surveys were conducted and the construction of the Nakai Dam, an extension dam 8.2 Status of Nam Theun endemic for the Theun-Hinboun Reservoir was fishes built on the Nam Gnouang, flooding the remaining intact habitat of the species. The construction of dams and reser- This underlines the need of a basin- voirs unavoidably has severe impacts wide management of aquatic biodiver- on aquatic habitats and aquatic biodi- sity. The other endemic rheophilic spe- versity. The impact on rheophilic spe- cies not present upstream of Nakai cies could be a serious issue because Reservoir (Rhinogobius lineatus)isa these species not only have a limited smaller fish with different habitat 34 M. Kottelat requirements. Although still a biodiver- ACKNOWLEDGMENTS sity important species, it seems in a The research summarised here safer situation with its range apparently results from several surveys conducted extending above FSL of the Theun- for the Nam Theun 2 Power Company Hinboun extension Reservoir. (NTPC) in Lao PDR whose sharehold- The rivers in the NPA are presently ers are Electricité de France, Lao Hold- the best known remaining habitat for ing State Enterprise, and Electricity the endangered Luciocyprinus striola- Generating Public Company Limited of tus and potentially the only one where Thailand. the species has chances to survive. Over the year, I benefitted from the This assumes that the aquatic habitats support of many managers and staff of be managed with the same attention as NTPC, especially in the early years terrestrial habitats. François Obein and Peter Goldston. While most of the original habitat of Likewise, the field work would not have the species endemic to the swamps of been successful without the assistance Nakai Plateau is inundated, two are of a great number of villagers, local abundant along the shores of the reser- workers, NTPC staff (especially Phoutha- voir and do not seem of concern. The kone Luangyotha, Stuart Gillon, Kham- third one (Oryzias sp. 'swamp') had keng Yuena), researchers and staff become very rare and has now been of LARREC (Kongpheng Boua- rediscovered and is the subject of spe- khamvongsa, Sinthawong Viravong, cific studies and its future is now Khamtanh Vatthanatham) and other expected to be safer. collaborators (Soutchai Khamphousay, The status of Rhodeus laoensis is Tan Heok Hui, Leong Tzi Ming). I thank not clear. It has been recorded Katsuma Kubota (Bangkok) for provid- upstream of Nakai Reservoir, but only ing information on spawning of Oryzias juveniles and at low density. The sup- sp. 'swamp'; Arthur E. Bogan (North posed host mussel is rare and in Carolina State Museum of Natural Sci- places in the NPA where juvenile bit- ences, Raleigh) for identification of the terlings had been collected the villag- mussels; Liankham Payasane (NTPC) ers were not even aware of the pres- for designing the map; and Maud Cottet ence of mussels. The two species (NTPC) for various information and need more attention. 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Systematic revision of Abell et al. : 37-39. Island Press, the balitorid loach genus Sewellia of Washington. The fishes of the Nam Theun and Xe Bangfai drainages, Laos 39 40 M. Kottelat Theun (raw outline) Distribution outside Xebangfai and Nam x Indo-West Pacific Oceans x x x x Nam Theun - Nam Gnouang endemic x Xe Bangfai endemic (cave) xxxx Mekong basin South and Southeast Asia x Mekong basin Mainland Southeast Asia Xe Bangfai Nam Theun x xxxxxx xxx xxxx Mekong andx Chao Phraya basins x Mekong basin Southeast Asia Mekong basin Mekong basin Mekong and Chao Phraya basins Mekong and Chao Phraya basins Mekong and Chao Phraya basins Southeast Asia Southeast Asia Mekong basin Mekong and Chao Phraya basins lower middle upper lower plateau upper headwaters Distribution of native fish species in the Xe Bangfai and Nam Theun basins by river sections. The name of species marked with aster- Répartition des espèces indigènes de poissons dans les bassins de la Xe Bangfai et de la Nam Theun par section de rivière. Les asté- Chitala ornata Anguilla marmorata (?) Clupeichthys aesarnensis Barbodes jacobusboehlkei * Barbonymus altus * Chitala blanci Notopterus notopterus Clupeoides borneensis Sundasalanx mekongensis * Amblypharyngodon chulabhornae Bangana elegans * Bangana musaei Barbodes aurotaeniatus * Barbodes rhombeus * Barbonymus gonionotus * Barbonymus schwanenfeldii * Boraras micros Cirrhinus microlepis Tenualosa thibaudeaui Anguillidae Clupeidae Notopteridae Sundasalangidae Cyprinidae Appendix 1. isks (*) has changed since 1996;Annexe older 1. names used inrisques various (*) reports indiquent and les publications espèces andsont dont equivalence listés le are nom dans listed a l’Annexe in changé 2. Appendix depuis 2. 1996 ; les anciens noms utilisés dans divers rapports, publications et leur équivalence The fishes of the Nam Theun and Xe Bangfai drainages, Laos 41 Theun (raw outline) Distribution outside Xebangfai and Nam x Southeast and East Asia x Vietnam, South China x x x xxx Nam Theun - Nam Gnouang endemic x x x Mekong basin in Laos Mekong, Red River and Yangtze basins x x x x x Mekong basin xxx Xe Bangfai endemic ? Mekong basin Mekong basin x Southeast Asia Xe Bangfai Nam Theun xx x x x Mekong and Chao Phraya basins Mainland Southeast Asia xxx xx xx xx x x xx xx xx xx x Mekong and Chao Phraya basins, x China Mekong and Chao x Phraya x Southeast basins Asia x Mekong and Chaox Phraya basins x x x x Southeast Asia Southeastx Asia x x x x x x Mainland Southeast Asia Mekong basin Southeast Asia Mekong basin Mekong basin Mekong basin Mekong and Chao Phraya basins Mainland Southeast Asia lower middle upper lower plateau upper headwaters . umbrifer cf Continued. . quangbinhensis (continued) Suite. . brevifilis sp. 'green'aff x Xe Bangfai endemic cf Discherodontus ashmeadi Epalzeorhynchos frenatum Epalzeorhynchos munense Esomus metallicus Folifer Devario Devario Garra cambodgiensis Garra fasciacauda Hampala dispar Crossocheilus atrilimes Crossocheilus oblongus * Crossocheilus reticulatus Cyclocheilichthys apogon Cyclocheilichthys armatus Cyclocheilichthys repasson Devario fangfangae * Garra cyrano Garra theunensis * Hampala macrolepidota Hemibarbus Henicorhynchus lobatus Henicorhynchus siamensis Hypsibarbus malcolmi Cirrhinus molitorella Hemiculterella macrolepis Henicorhynchus lineatus Cyprinidae Appendix 1. Annexe 1. 42 M. Kottelat Theun (raw outline) Distribution outside Xebangfai and Nam x x Mekong basin x x x x Middle Mekong basin x x x Mekong basin xx xxxx xxx Lower Mekong basin Mekong and Chao Phraya basins Mainland Southeast Asia Southeast Asia Middle Mekong basin Southeast Asia Southeast Asia xxxxxxx Southeast Asia Mekong, Chao Phraya and Salween basins Southeast Asia Mainland Southeast Asia Mainland Southeast Asia Mekong basin Mekong basin Xe Bangfai Nam Theun x xxx x Mekong and Chao Phraya basins Mekong and Chao Phraya basins Southeast Asia x xxx x x xx xxx xx x x Mainland Southeast Asia x Southeast Asia x Mekong basin in Laos x Mekong basin Mainland Southeast Asia Middle Mekong Southeast basin Asia lower middle upper lower plateau upper headwaters Continued. (continued) Suite. Onychostoma meridionale * Opsarius koratensis * Opsarius pulchellus * Oreichthys parvus Osteochilus lini Osteochilus melanopleura Osteochilus microcephalus Osteochilus striatus * Osteochilus vittatus * Osteochilus waandersii Hypsibarbus vernayi * Onychostoma fusiforme * Labeo chrysophekadion Labeo pierrei * Labiobarbus leptocheila Laocypris hispida Laubuka laubuca * Lobocheilos melanotaenia Lobocheilos rhabdoura Luciocyprinus striolatus Mekongina erythrospila Mystacoleucus atridorsalis Mystacoleucus chilopterus Mystacoleucus ectypus * Mystacoleucus greenwayi Mystacoleucus marginatus Neolissochilus blanci * Cyprinidae Appendix 1. Annexe 1. The fishes of the Nam Theun and Xe Bangfai drainages, Laos 43 Theun (raw outline) Distribution outside Xebangfai and Nam x Southeast Asia x Nam Theun endemic x x x x Mekong basin x xx x x Nam Theun endemic Nam Theun - Nam Gnouang endemic x Mekong and Chao Phraya basins x x x x x x Mekong and Chao Phraya basins xxx x x x Mekong x basin in Yunnan Mainland Southeast Asia Mainland and Southeast South Asia Asia Xe Bangfai Nam Theun xxxxx xx Southeast Asia x Mekong and Chao Phraya basins Mekong basin x Mekong and x Chao Phraya Mekong basins and Chao Phraya basins Mekong basin Mekong basin xxx xxx x xx xx xx x xx x x xx x x Mekong basin Mekong basin Middle Mekong Mekong basin basin Mainland Southeast Asia Mainland Southeast Asia Southeast Asia Mekong and Chao Phraya Southeast drainages Asia Mekong and Chao Phraya basins lower middle upper lower plateau upper headwaters Continued. (continued) Suite. Oxygaster pointoni Parachela oxygastroides Parachela siamensis Paralaubuca barroni Paralaubuca riveroi Paralaubuca typus Poropuntius carinatus Scaphognathops bandanensis Scaphognathops stejnegeri Scaphognathops theunensis * Poropuntius laoensis Raiamas guttatus Scaphiodonichthys acanthopterus Sikukia gudgeri Poropuntius normani Probarbus labeaminor Puntioplites falcifer Puntius brevis Rasbora atridorsalis Rasbora borapetensis Rasbora daniconius Rasbora myersi * Rasbora paviana Rasbora atridorsalis Rasbora trilineata Rhodeus laoensis * Tor ater Cyprinidae Appendix 1. Annexe 1. 44 M. Kottelat Theun (raw outline) Distribution outside Xebangfai and Nam x x Nam Theun endemic xx xx Southeast Asia Southeastx Asia x xx xx x xx Middle Mekong x basin x x Nam Theun endemic xx x x x x Nam Theun endemic x x Nam Theun endemic x Middle Mekong basin Middle Mekong x basin Nam Theun endemic x x x x Mekong basin xx x x Annamite Range Mekong and Red River basins in Yunnan x x xx Mainland Southeast Asia xx x Mekong basin in Cambodia and Southern Laos Middle Mekong basin Mekong basin xx x Xe Kong basin in Cambodia Mekong basin in Cambodia Xe Bangfai Nam Theun x xx x xx xx x x x x x x x Mekong basin Mainland Southeast Asia Mekong basin Mekong and Chao Phraya basins lower middle upper lower plateau upper headwaters Continued. (continued) . annamitica Suite. cf Annamia normani Schistura cataracta Schistura kongphengi * Schistura nudidorsum * Gyrinocheilus aymonieri Balitora Balitoropsis sexmaculata * Homalopteroides smithi * Nemacheilus longistriatus Schistura daubentoni Schistura dorsizona * Schistura isostigma * Schistura nicholsi Schistura obeini * Balitora lancangjiangensis Balitoropsis yunnanensis * Hemimyzon papilio * Nemacheilus arenicolus * Nemacheilus pallidus Nemacheilus platiceps Schistura atra * Tor tambroides Tor laterivittatus * Tor tambra Cyprinidae Balitoridae Gyrinocheilidae Nemacheilidae Appendix 1. Annexe 1. The fishes of the Nam Theun and Xe Bangfai drainages, Laos 45 Theun (raw outline) Distribution outside Xebangfai and Nam x x Nam Theun endemic x x East Asia x x x x Middle Mekong basin x x Nam Theun-Nam Gnouang endemic x x Mekong and Chao Phraya basins x Mekong basin xx Middle Mekong basin Mekong basin xxx x x Mekong basin Mainland Southeast Mainland Asia Southeast Asia Xe Bangfai Nam Theun xx xx x x Mainland Southeast Asia Mekong and Chao Phraya basins Mekong basin x x Mekong basin x xxx xx Xe Bangfai endemic Mekong and Chao Phraya basins Mekong basin Mekong basin lower middle upper lower plateau upper headwaters Xe Bangfai x Mekong basin Nam Theun x x Nam Theun endemic ? . misgurnoides (continued) aff Continued. sp. 'dwarf males'sp. 'large spots'sp. 'small spots'sp. 'vertical spots' x x x x x Xe Bangfai endemic ? Mekong and Chao Mainland Phraya Southeast basins Asia Xe Bangfai endemic ? . fusca . fusca . anguillaris sp. 'Nam Kathang' x Xe Bangfai endemic Suite. aff aff aff Syncrossus helodes * Syncrossus beauforti * Ambastaia nigrolineata * Pangio Serpenticobitis zonata * Pangio Schistura punctifasciata * Schistura sombooni * Schistura tubulinaris * Schistura Acanthopsoides delphax Acanthopsoides gracilentus Acanthopsoides hapalias Acantopsis Acantopsis Acantopsis Acantopsis Lepidocephalichthys furcatus Lepidocephalichthys hasselti Lepidocephalichthys zeppelini Microcobitis Misgurnus anguillicaudatus Pangio Yasuhikotakia caudipunctata * Yasuhikotakia eos * Yasuhikotakia lecontei * Botiidae Serpenticobitidae Nemacheilidae Cobitidae Appendix 1. Annexe 1. 46 M. Kottelat Theun (raw outline) Distribution outside Xebangfai and Nam x Mekong basin xx Mekong basin xx x Mainland Southeast x Asia x x Southeast Asia Southeast and South Asia ? x x x Nam Theun + Nam Gnouang endemic Xe Bangfai Nam Theun xxx xxxx xx xx x xxxxx x xx Mekong basin x Mekong and Chao x Phraya basins Southeast Asia Mekong andx Chao Phraya basins Mekong and Chao Phraya Southeast basins Asia Mainland Southeast Asia x Lower Mekong basin x Southeast Asia Southeast Asia Southeast Asia Mekong and Chao Phraya basins Mainland Southeast Asia Mekong and Chao Phraya basins Mekong basin ? lower middle upper lower plateau upper headwaters * 1 . fuscus aff Continued. Suite. (continued) Mystus atrifasciatus Laides longibarbis Hemibagrus nemurus Hemibagrus filamentus Hemibagrus wyckioides Mystus mysticetus Mystus singaringan Pseudomystus siamensis Amblyceps serratum * Belodontichthys truncatus Kryptopterus bicirrhis Kryptopterus cryptopterus Micronema apogon * Micronema cheveyi * Pterocryptis inusitata * Pangasius larnaudii Clarias batrachus Yasuhikotakia longidorsalis Yasuhikotakia modesta * Bagarius yarrelli Glyptothorax Botiidae Schilbidae Bagridae Amblycipitidae Siluridae Pangasiidae Clariidae Sisoridae Appendix 1. Annexe 1. The fishes of the Nam Theun and Xe Bangfai drainages, Laos 47 Theun (raw outline) Distribution outside Xebangfai and Nam Xe Bangfai endemic ? x x Nam Theun endemic xx xxx x x Mekong basin x x Salween and Mekong basins Nam Theun endemic Middle Mekong basin Nam Theun endemic x x x x Mekong and Chao Phrayax basins Southeast Asia Xe Bangfai Nam Theun xx Southeast Asia Mekong basin xxx xx xx xx x x Middle Mekong basin Middle Mekong basin Southeast Asia Mekong basin Mainland Southeast Asia Mainland Southeast Asia lower middle upper lower plateau upper headwaters 2 . zanaensis . fuscus sp. 'slender' x Nam Theun - Nam Gnouang endemic ? aff aff Continued. Suite. (continued) sp. 'river' *sp. 'swamp' * x x Nam Nam Theun Theun endemic endemic Nandus oxyrhynchus Glyptothorax horai * Glyptothorax laosensis Glyptothorax Oreoglanis hypsiurus * Pseudecheneis sympelvica * Akysis inermis Akysis varius * Monopterus javanensis * Oryzias mekongensis Oryzias pectoralis Oryzias Oryzias Xenentodon canciloides * Doryichthys contiguus * Parambassis siamensis Parambassis Glyptothorax Oreoglanis lepturus * Toxotes microlepis Nandidae Akysiidae Synbranchidae Adrianichthyidae Belonidae Syngnathidae Ambassidae Sisoridae Toxotidae Appendix 1. Annexe 1. 48 M. Kottelat Theun (raw outline) Distribution outside Xebangfai and Nam x Nam Theun - Nam Gnouang endemic xx x x x Mekong basin Southeast and South Asia x x x x x Southeast and South Asia xxxx x Xe Bangfai endemic Southeast and South Asia Mekong basin Southeast Asia Xe Bangfai Nam Theun xx Southeast Asia Mainland Southeast Asia xx xx x x x xxx Southeast Asia Mekong basin Mekong basin x x Mekong basin Southeast Asia xxxx xx x x x x Southeast Asia Mekong basin Mekong basin Mekong basin Mekong basin lower middle upper lower plateau upper headwaters Continued. . marulius Suite. aff Channa micropeltes Channa striata Chaudhuria caudata Datnioides undecimradiatus * Neodontobutis aurarmus * Channa gachua Channa Pristolepis fasciata Oxyeleotris marmorata Brachygobius mekongensis Gobiopterus chuno Papuligobius ocellatus * Rhinogobius lineatus * Betta smaragdina Osphronemus exodon Anabas testudineus Terateleotris aspro * Trichopsis vittata Trichopodus trichopterus * Trichopsis schalleri * Chaudhuriidae Datnioididae Odontobutidae Channidae Pristolepididae Eleotrididae Gobiidae Osphronemidae Anabantidae Appendix 1. Annexe 1. The fishes of the Nam Theun and Xe Bangfai drainages, Laos 49 Theun (raw outline) Distribution outside Xebangfai and Nam x Mainland Southeast Asia x Mekong basin x Middle Mekong basin Xe Bangfai Nam Theun xxx xx x x x x x x x Southeast Mekong and and South Chao Asia Phraya Mekong basins and Chao Phraya basins Mekong and Chao Phraya basins xxx x x x Southeast Asia Mekong and Nan basins Mekong basin lower middle upper lower plateau upper headwaters (continued) Continued. Suite. Chaudhuria fusipinnis Macrognathus semiocellatus Macrognathus siamensis Mastacembelus armatus * Brachirus harmandi * Auriglobus nefastus Pao suvattii * Pao abei * Pao cochinchinensis * Pao turgidus * Chaudhuriidae Mastacembelidae Soleidae Tetraodontidae Appendix 1. Annexe 1. 50 M. Kottelat

Appendix 2. Species appearing under a different name in earlier reports, publication and in Kottelat (2001). Annexe 2. Espèces apparaissant sous un nom différent dans de précédents rapports, publication et dans Kottelat (2001). Present name Earlier name Akysis varius Akysis sp. n. aff. heterurus Ambastaia nigrolineata Botia cf. nigrolineata, Yasuhikotakia nigrolineata Amblyceps serratum Amblyceps sp. n. aff. mangois Bangana elegans Bangana sp. n. aff. sinkleri Barbodes aurotaeniatus Puntius aurotaeniatus Barbodes jacobusboehlkei Puntius jacobusboehlkei Barbodes rhombeus Puntius rhombeus Barbonymus altus Barbodes altus Barbonymus gonionotus Barbodes gonionotus Barbonymus schwanenfeldii Barbodes schwanenfeldii Brachirus harmandi Euryglossa harmandi Crossocheilus oblongus Crossocheilus siamensis Datnioides undecimradiatus Coius undecimradiatus Devario fangfangae Danio aff. strigillifer Doryichthys contiguus Doryichthys deokhatoides Garra theunensis Garra cf. pingi Glyptothorax aff. fuscus 1 Glyptothotrax lampris Glyptothorax horai Glyptothorax macromaculatus Hemimyzon papilio Hemimyzon sp. n. aff. elongata Hypsibarbus vernayi Barbodes daruphani Labeo pierrei Labeo yunnanensis Laides longibarbis Laides hexanema Laubuka laubuca Chela laubuca Mastacembelus armatus Mastacembelus armatus and M. favus Micronema apogon Kryptopterus apogon Micronema cheveyi Kryptopterus cheveyi Monopterus javanensis Monopterus albus Nemacheilus arenicolus Nemacheilus sp. n. aff. pallidus Neodontobutis aurarmus Odontobutis aurarmus Neolissochilus blanci Neolissochilus stracheyi Onychostoma fusiforme Onychostoma cf. elongata Onychostoma meridionale Onychostoma sp. n. cf. elongata Opsarius koratensis Barilius koratensis Opsarius pulchellus Barilius pulchellus Oreoglanis lepturus Oreoglanis delacouri (in part) Oreoglanis hypsiurus Oreoglanis delacouri (in part) Oryzias pectoralis Oryzias sinensis (in part) Oryzias sp. 'river' Oryzias sinensis (in part) Oryzias sp. 'swamp' Oryzias sinensis (in part) The fishes of the Nam Theun and Xe Bangfai drainages, Laos 51

Appendix 2. Continued. Annexe 2. Suite. Present name Earlier name Osteochilus striatus Osteochilus sp. n. aff. sarawakensis Osteochilus vittatus Osteochilus hasselti Pao abei Tetraodon sp. n. yellow spots Pao suvattii Tetraodon suvattii Papuligobius ocellatus Rhinogobius ocellatus Pseudecheneis sympelvica Pseudecheneis sp. n. Pterocryptis inusitata Pterocryptis cochinchinensis Rasbora myersi Rasbora dusonensis Rhinogobius lineatus Rhinogobius mekongianus Rhodeus laoensis Rhodeus sp. n. aff. spinalis Scaphognathops theunensis Scaphognathops sp. n. red caudal Schistura atra Schistura sp. n. black Schistura dorsizona Schistura sp. n. saddles Schistura isostigma Schistura geisleri Schistura kongphengi Schistura cf. kengtungensis Schistura nudidorsum Schistura sp. n. naked back Schistura obeini Schistura sp. n. red tail Schistura punctifasciata Schistura sp. n. narrow bars Schistura sombooni Schistura aff. breviceps Schistura tubulinaris Schistura sp. n. tubular naris Serpenticobitis zonata new genus new species Sundasalanx mekongensis Sundasalanx aff. microps Syncrossus beauforti Botia beauforti Syncrossus helodes Botia helodes Terateleotris aspro Odontobutis sp. n. Tor laterivittatus Tor sp. n. red fins Toxotes microlepis Toxotes chatareus Trichopodus trichopterus Trichogaster trichopterus Xenentodon canciloides Xenentodon sp. n. large scales Yasuhikotakia caudipunctata Botia caudipunctata Yasuhikotakia eos Botia eos Yasuhikotakia lecontei Botia lecontei Yasuhikotakia modesta Botia modesta Yasuhikotakia longidorsalis Botia longidorsalis