Japanese Journal of Ichthyology 魚 類 学 雑 誌 Vol.21,No.3.1974 21巻3号1974年

New Species of the Genus Scaphognathops, Cyprinidae,from the Lao Mekong River System

Yasuhiko Taki (Received July 4,1974)

Abstract A new cyprinid species,Scaphognathops mekongensis,is described from the Lao Mekong and its tributaries.The new species is distinguished from its only con- gener,S.stejnegeri,primarily by its much wider lower jaw,less developed lower lip, broader interorbital space,fewer numbers of branched rays in the dorsal and anal fins, and more numerous gill-rakers.On the other hand,S.mekongensis agrees with S. stejnegeri in the basic formation of the snout and mouth,structures of the principal simple dorsal and anal rays,squamation,shape and arrangement of the pharyngeal teeth,number of the vertebrae,and principal body proportions.These similarities clearly indicate their close relationship,and seem sufficient to recognize the new species as congeneric with S.stejnegeri.Status of the genus Scaphognathops still remains ob- scure.On the basis of similarities in the features of the mouth region and simple dorsal rays,the genus appears related to the Southeast Asian genus Scaphiodonichthys. Scaphiodonichthys acanthopterus is also recorded from Laos.

Introduction mouth region and some meristic characters.

Described herein is a new cyprinid species These specimens were tentatively identified as referred to the genus Scaphognathops collected Scaphognathops sp.in Taki(1974:146).Sub- in the Mekong River and its tributaries in sequent study of this species has confirmed central and southern Laos. the adequacy of its assignment to Scapho- The genus Scaphognathus was proposed by gnathops,and revealed many unique characters Smith(1931:21-22)for Scaphognathus stejne- that warrant its recognition as a new species. The description of Scaphognathops mekongensis geri,which was described from a single speci- men taken from the Mekong in northeastern is based on a total of 33 type specimens and Thailand.Smith characterized the genus by 29 other samples collected from the Mekong the combination of deep body,absence of system in Laos.A descriptive note,based on barbels,highly modified lower jaw formed six specimens from the same area,is also into a sharp-edged,slender,bony scoop with made of S.stejnegeri in order to supplement lower lips restricted to sides and defficient its original description and compare it with medially,an osseous and denticulated principal the present new species. simple dorsal ray followed by numerous branched rays,and an osseous and entire Material and methods principal simple anal ray followed by six Type specimens and other samples of S. branched rays.The generic name was later mekongensiswere deposited at the National replaced with Scaphognathops(Smith,1945: ScienceMuseum,Tokyo(NSMT-P)and the 208)because of the preoccupation of Scapho- Institute for BreedingResearch,Tokyo Uni- gnathus in reptiles.Since the original de- versity of Agriculture(IBRP).Collecting data scription,there had been no record of the for S.mekongensisand S.stejnegeri are shown genus until Taki(1968:4,12)reported its preceding the description of each species. occurrence in Laos. Measurementswhich requireexplanation are In the course of my 1970•`1971 collection as follows:Head length includes opercular of fish in Laos,I came across a number of flap;length of caudal fin is expressed as the specimens which are referable to the genus distance from the base of middle caudal ray Scaphognathops but apparently differ from S. to the tip of the upper lobe of the fin.All stejnegeri in their overall appearances of the measurementswere made with dial calipers,

―129― 魚 類 学 雑 誌Japan.J.Ichthyol.21(3).1974

Fig.1.Scaphognathops mekongensis sp.nov.holotype,140.0 mm SL,NSMP-P.17881:collected in the Mekong River at Hatsalao,southern Laos.on Apr.23.1971.

read to the nearest 0.1mm,and are ex- designated as paratypes:1 specimen,134.0 mm pressed as percent of standard length(SL)or SL,collected with the holotype,NSMT-P. head length(HL).Some counts employed in 17882;1,157.5 mm SL,from the type locality, this study require explanation as follows: Apr.2,1971,IBRP 5451;27(3 cleared:1,

Lateral line scale counts include all tube- 90.2 mm SL—Fig.2A;1,105.2 mm SL—Fig. hearing scales on the caudal On scale counts 3A),76.9•`154.5 mm SL,Mekong R.at mouth

for transverse series above lateral line are of Bang Lieng R.and Bang Lieng R.near its

made for the left side series containing the mouth,at Bang Lieng,about 50 km south of posteriormost free-margined predorsal scale Pakse,southern Laos,May 26,1970,IBRP and those below lateral line are for the series 4028;1,80.0 mm SL,Mekong R.at the Khong

including the posteriormost free-margined Falls.southern Laos,Jun.2,1970,IBRP preanal scale,and the predorsal or preanal 4957;1,91.0 mm SL,Mekong R.at Sithan scale is counted as 0.5;predorsal scale counts Tay,near Vientiane,central Laos,May 9, are expressed as a number of free-margined 1971,IBRP 5751;1,83.6mm SL,Nam Khon scale mounting on the median dorsal line. R.about 1 km upstream from its mouth to Counts for vertebrae and vertical fin rays and Nam Ngum R.,near Tha Ngon,central Laos, observation of skeletons were made on radio- Jun.17,1970.IBRP 4830. graphs. Other material—Twenty-nine juvenile speci- mens vere collected:20,49.2•`61.0 mm SL.

Scaphognathops mekongensis,sp.nov. Mekong R.at Sithan Tay,near Vientiane. (Figs.1,2A,3A) central Laos,Apr.9,1971,IBRP 5519:9. Scaphognathops sp.Taki,1974:146,fig.141. 50.0•`62.2 mm SL,locality as IBRP 5519 above, Mekong River at Sithan Tay,Hatsalao,Bang Apr.10,1971,IBRP 5571. Lieng and the Khong Falls,Laos,Nam Khon R.near Tha Ngon,Laos,Bang Lieng Diagnosis R.at Bang Lieng,Laos(description). A species of the genus Scaphognathops with Holotype-140.0 mm SL,sex not deter- terminal or subinferior mouth,wide lower

mined,collected in the Mekong River at jaw,and minute,rudimentary lower lip con- Hatsalao,near Pakse,southern Laos,on Apr. fined to each side of lower jaw near corner

23.1971,by the author.by means of beach of mouth;branched dorsal soft rays 9,branch- seine.Cat.No.NSMT-P.17881.(Fig.1) ed anal soft rays 5,gill-rakers 3•`5+12•`13 Paratypes-A total of 32 specimens were =16•`18.

―130― Taki:New Cyprinid Species of Scaphognathops

Description forming a sharp,wide,horny edge;the edge Except where otherwise noted,the de- consisting of a horny sheath V-shaped in scription is based on the holotype and 32 vertical section,overhung by upper lip when paratypes.Counts for fin rays,scales,gill- mouth is closed,connected with thick layers rakers and vertebrae are given in Table 1; of gnathic muscle covered by thick skin(Fig. proportional measurements are in Table 2. 2A).No barbels.Nostrils nearer to eye than Body deep,compressed;greatest depth at tip of snout.Eyes large,with a narrow but origin of dorsal fin;caudal peduncle strongly distinct eyelid-like margin.Preoperculum and compressed.Head small,short;interorbital operculum rather narrow;opercular flap space moderately wide.Tip of snout bluntly broad. pointed,prominent,forming a pendulous Gill-rakers small,short;those on upper rostral fold(terminology following Weber and limb slender;those on lower limb coarsely de Beaufort,1916)covering upper lip medial- set,conical to papillate.Pharyngeal teeth ly;a lateral fold(new term)on each side of (from 3 specimens,IBRP 4028)biserial,3.5- snout,covering upper lip laterally(Fig.2A). 5.3;teeth in outer row small,slender,some - Mouth small,terminal to subinferior;upper what hooked;uppermost tooth in main row lip thin,separated from rostral fold by a (5th tooth in main row,according to the de- deep groove,connected with lower lip around finition by Chu,1935)greatly recurved,distal mouth corners;lower lip rudimentary,re- portion swollen,edging in a spoon-like hook, stricted to each side of lower jaw near mouth grinding surface oblique,entire;lowermost corner and broadly defficient medially,se- tooth in main row(1st tooth in main row, parated from skin of chin by shallow post- according to Chu,1935)small,with a rounded labial grooves;front margin of lower jaw tip;remaining three theeth in main row well Table 1.Counts for meristic characters and their frequencies and means for 62 specim S. ens of mekongensis and 6 specimens of S.stejnegeri.Gill-raker counts are from IBRP 4028(7 specimens),5451(1)and 5519(7) .

―131 ― 魚 類 学 雑 誌Japan.J.Ichthyol.21(3),1974 developed,not much compressed,little hooked, flexible;interhemal spine of principal simple ray inserted between hemal spines of 21st and grinding surface broad,oblique,entire(Fig. 3A). 22nd or rarely 22nd and 23rd vertebrae. Lateral line complete,decurved downward Caudal fin broad,deeply forked;each lobe running in lower side of trunk and in middle pointed.Pelvic fins slightly shorter than of caudal peduncle,extending posteriorly to pectoral fins,extending slightly beyond vent, two or three scales on caudal fin;sensory with a free axillary scale. tubes simple.Scales large except those on Coloration of fresh-caught specimens.Body thorax.Dorsal fin high,with a low scaly uniformly silvery,top of head and back of sheath along anterior portion of its base,free body dark with grayish to bluish tint,ventral (=distal)margin concave;simple soft rays surface of body whitish.Operculum silver osseous;principal(=4th)simple ray elongate, to golden.Each scale on back and sides with distal 1/4 to 1/3 flexible,serrated with about a black,crescent base.Membranes of verti- 15 denticles along its hind margin;origin of cal fins blackish,paired fins pale yellow, dorsal fin about midway between tip of snout sparsely covered with dark melanophores. and base of caudal fin and opposite to or Distribution-S.mekongensis occurs in main- slightly in advance of insertion of pelvic fins; streams and affluents of the lower Mekong. interneural spine of principal simple ray in- In central Laos it was collected at Tha Ngon serted between neural spines of 11th and 12th and Sithan Tay;in southern Laos it was or rarely 12th and 13th vertebrae.Anal fin with a basal scaly sheath,free margin concave; simple soft rays osseous;principal(=3rd) simple ray prolonged,entire,distal 1/6 to 1/5

Fig.2.Lateral and ventral aspects of snout and mouth:A)Scaphognathops me- kongensis(90.2mm SL)and B)Scapho- gnathops stejnegeri(88.5 mm SL).Ab- breviations:bc,horny edge of lower Fig.3.Fronto-dorsal aspects of pharyngeals and their teeth:A)Scaphognathopi jaw;lf,lateral fold;11,lower lip;ms, gnathic muscle;rf,rostral fold;ul, mekongensis(105.2mm SL)and B) Scanhognathovs ste inegeri(64.0mm SL). upper lip.

―132― Taki:New Cyprinid Species of Scaphognathops

found from Hatsalao,Bang Lieng,south to edge;chin narrow,with thin layers of gnathic the Khong Falls near the Cambodian border. muscle covered by thick skin(Fig.2B).No The species probably ranges further southward barbeles.Eyes large,with a narrow but dis- in the Cambodian Mekong,but the collection tinct eyelid-like margin.Opercular flap broad. data indicate that the fish does not inhabit, Gill-rakers small,coarsely set;those on or rarely inhabits,northern Laos.S.mekon- upper limb slender: those on lower limb

gensis is sympatric with S.stejnegeri. conical to papillate.Pharyngeal teeth biserial, Etymology-Distribution of the species is 3.5.5.3;teeth in outer row small,slender, apparently restricted to mainstreams and somewhat hooked:those in main row large branches of the Mekong River,from which except lowermost(1st tooth in main row, it was named. according to Chu,1935)round-tipped tooth, not much compressed,little hooked,grinding Scaphognathops stejnegeri(Smith) surface broad,oblique,entire(Fig.3B). Figs.2B,3B)( Lateral line complete,sensory tubes simple. Scaphognathus stejnegeri Smith,1931:22•`23, Dorsal fin with a basal scaly sheath;principal figs.10,11,Mekong River near Ban (=4th)simple soft ray prolonged,osseous, deMekong,northeastern Thailand(original denticulated behind;origin of dorsal fin op- scription):holotype,USNM 90303. posite to or slightly in advance of insertion Scaphognathops stejnegeri;Smith,1945:208 of pelvic fins;interneural spine of principal 209,fig.36(generic •` name to replace simple ray inserted between neural spines of Scaphognathus,preoccupied in reptiles;re- 11th and 12th or 12th and 13th vertebrae. ference to original description):Taki,1968: Anal fin with a basal scaly sheath;principal 4,12,fig.13,Mekong R.at Vientiane, (=3rd)simple soft ray long,osseous,entire; market at Pakse,Laos(in list,range),1974: interhemal spine of principal simple ray in- 145,fig.140,Nam Khon R.at Tha Ngon, serted between hemal spines of 21st and 22nd Mekong R.at the Khong Falls,Laos(de- vertebrae. scription). Coloration of fresh-caught specimens.Body Material examined-1 specimen,63.5 mm silverey,back dark,ventral surface whitish. SL,collected in the Mekong R.at the Khong Each scale on back and sides with a dark Falls,southern Laos,on Jun.2,1970,NSMT-P crescent base.All fins with blackish mem- 17883;2(1,64.0 mm SL—cleared,Fig.3B), branes. 46.0 and 64.0 mm SL,Nam Khon R.about 1 Distribution-S.stejnegeri has been recorded km upstream from its mouth to Nam Ngum in the lower Mekong basin from Vientiane, R.,near Tha Ngon,central Laos,Jun.17, Laos south to the Khong Falls near the 1970,IBRP 4378;1,88.5 mm SL,locality as boundary between Laos and Cambodia.This IBRP 4378 above,July.18,1970,IBRP 4410 species is sympatric with S.mekongensis,and (Fig.2B). apparently does not occur,or rarely occurs, Descriptive note-Body deep,compressed; in the upper Mekong. greatest depth at origin of dorsal fin.Head Remarks—The Laotian specimens examined small;interorbital space narrow.Snout in this study do not agree with the description pointed,forming a rostal fold covering upper of the holotype(Smith,1931:22=23)in the lip medially and a lateral fold on each side number of the predorsal scales.Whereas the covering upper lip laterally(Fig.2B).Mouth scale count is 12 in the holotype,it is invaria- small,terminal,oblique;upper lip thick, bly 9 in the specimens at hand.The differ- separated from rostral fold by a deep groove, ence may have resulted from differences in connected withlower lip around mouth counting methods. corners;lower lip thick,fleshy,restricted to each side of lower jaw and defficient medially, Comparison of S.mekongensis and separated from skin of chin by postlabial S.stejengeri,and discussion on their status grooves laterally;median portion of lower Despite the divergent appearances of the jaw forming a sharp,narrow,scoop-like,horny mouth region,S.mekongensis and S.stejnegeri

―133― 魚 類 学 雑 誌Japan.J.Ichthyol.21(3),1974

Table 2.Measurements in percent of standard length or head length of the holotype and 32 paratypes of S.mekongensis and five specimens of S.stejnegeri.and N for S.mekon- gensis are calculated on both holo-and paratypes.

share all fundamental structural characters of degree of modification of the parts of the the snout and mouth.The snout has a rostral mouth region:S.mekongensis has a more fold on front and lateral folds on sides; rounded snout,a lower-positioned mouth,less barbels are absent;the lower jaw forms a developed lower lips(Figs.2A,B),a much sharp horny edge;the lower lip is defficient wider lower jaw(Figs.2A,B;Table 2),and medially and restricted to sides of the lower a wider interorbital space(Table 2). jaw(Figs.2A,B).The two species are also The discovery of the second species of similar in the structures of the principal simple Scaphognathops requires the following emenda- dorsal and anal rays(osseous and denticulated tion of the generic diagnosis by Smith(1931: in the dorsal and osseous and entire in the 21•`22):Mouth terminal to subinferior;lower anal),arrangement and shape of the pharyn- jaw narrow or broad;lower lip rudimentary geal teeth(Figs.3A,B),squamation(Table 1), or large and thick;branched dorsal rays more number of the vertebrae(Table 1),and the than 9;branched anal rays 5 or 6;pharyn- body proportions(Table 2). geal teeth biserial,3.5-5.3.The two species S.mekongensis and S.stejnegeri are different of the genus can be distinguished by the in the number of the branched dorsal and anal following key: rays and gill-rakers(Table 1).The two species 1.Branched dorsal rays 9;branched anal are also distinguishable by the shape and rays 5;total gill-rakers 16•`18;interorbital

―134― Taki:New Cyprinid Species of Scaphognathops

width more than 37% of head length;width Chu(1935)on pharyngeals and their teeth in of lower jaw at mouth corners more than Chinese cyprinids,the two-rowed pharyngeal 22% of head length;lower lip rudimentary•c teeth in Scaphognathops may be an exceptional S.mekongensis,sp.nov. case in the subfamily Barbinae,in which the 2.Branched dorsal rays 13•`15;branched teeth are arranged mostly in three rows or anal rays 6;total gill-rakers 11•`12;inter- the genus may be included in a subfamily orbital width less than 36% of head length; other than the Barbinae. width of lower jaw at mouth corners less than In a sense of postscript the record of the 11% of head length;lower lip thick,fleshy species below is appended. •cS.stejnegeri Scaphiodonichthys acanthopterus(Fowler)-1 Relationship of Scaphognathops with other specimen(cleared),59.4mm SL,collected in cyprinid genera are difficult to interprete. the Nam Done River near Luang Prabang, Smith(1931:21•`22),who compared the genus northern Laos,on Jun.15,1970,Cat.No. with the East Asian genus Sarcocheilichthys, IBRP 4152;4,48.6•`51 .0mm SL,Nam Mo stated that in some members of Sarcocheilichthys R.at Nam Mo,central Laos,Apr.22,1974, the lower jaw is somewhat similar to that of. IBRP 6076. Scaphognathops,but the mouth is inferior and the principal simple dorsal ray is neither Acknowledgements strongly ossified nor denticulated.The South Dr.Fujio Yasuda and Kiyoshi Fujita, and Southeast Asian genus Aspidoparia also Tokyo University of Fisheries,and Tousei has a bony-edged lower jaw without lip, Urushido,the Institute for Breeding Research, however,according to Smith(1945:123),the Tokyo University of Agriculture,have been

principal simple dorsal ray is not osseous and of great help in the preparation of the manu- entire. script.Sincere appreciation is also extended The Southeast Asian genus Scaphiodonichthys to Dr.Norio Kondo,the Institute for Breed- shows a close affinity to Scaphognathops in ing Research,Tokyo University of Agricul- many respects.I have examined five specimens ture,and Dr.Katsuzo Kuronuma,for their of Scaphiodonichthys acanthopterus(originally invaluable suggestions given to my work on described under the generic name Scaphiodon- Southeast Asian fishes. thopsis by Fowler,1934:119).In this species the formation of the mouth region is similar Literature cited

to that of Scaphognathops except that the Chu, Y. T. 1935. Comparative studies on the lateral folds are inconspicuous or absent and scales and on the pharyngeals and their teeth the lower lip is vestigial.The principal simple in Chinese cyprinids, with particular reference to taxonomy and evolution. Biol. Bull. St. dorsal ray is also osseous and serrated.Ac- John's Univ., Shanghai, 2:i•`x, 1•`225, pls. 1 cording to Fowler(1934;119),however,the 30. •` pharyngeal teeth are triserial,with a dental Fowler, H. W. 1934. Zoological results of the formula 2.3.5 •`4.3.1. third de Schauensee Siamese expedition. Part Sorescu(1968),on the basis of their pectoral 1. Fish. Proc. Acad. Nat. Sci. Philadelphia, 86: girdles,assigned Sarcocheilichthys and Aspido- 67•`163, figs. 1•`129, pl. 12. paria to the subfamilies Gobioinae and Smith, H. M. 1931. Description of new genera

Cultrinae respectively.For Scaphognathops and species of Siamese fishes. Proc. U . S. Nat. and Scaphiodonichthys,however,no attempt Mus., 79, art. 7: 1•`48, figs. 1•`22, 1 pl. has been made by recent authors to clarify Smith, H. M. 1945. The fresh-water fishes of Siam, their status of subfamily level.I have placed or Thailand. U. S. Nat. Mus. Bull., 188: i•`xi, 1•`622, figs. 1•`107, pls. 1•`9. both Scaphiodonichthys and Scaphognathops in Sorescu, C. 1968. Vergleichende Untersuchun- the subfamily Barbinae(Taki,1974:144•`146), gen uber den Schultergurtel der Cyprinidae. but,as noted in that article,the assignment Senckenbergiana Biol., 49 (5): 387•`397, figs. 1 is provisional.Based on my observation of 16. •` pharyngeal teeth in Southeast Asian cyprinids Taki, Y. 1968. Notes on a collection of fishes (unpublished)and the comprehensive work by from lowland Laos. U. S. Agency for Interna-

―135― 魚 類 学 雑 誌Japan.J.Ichthyol.21(3),1974

ら れ て い た. tional Development, Mission to Laos: 1•`47, 1 text-fig., figs. 1•`51. 本 新 種 は,下 顎 と そ の 角 質 縁 が 幅 広 く,下 唇 の 発 達 が き わ め て 悪 く,背 鰭 分 枝 軟 条 数9,臀 鰭 分 枝 軟 条 数 Taki, Y. 1974. Fishes of the Lao Mekong basin. 5.鯉 耙 数3～5+12～13=16～18を 有 す る 点 で,下 顎 U. S. Agency for International Development, Mission to Laos: i•`vii, 1•`232, figs. 1•`191. と角 質 縁 の 幅 が 狭 く,下 唇 が 比 較 的 大 き く,背 臀 分 枝

Weber, M. and L. F. de Beaufort. 1916. The 軟 条 数13～15.臀 鰭 分 枝 軟 条 数6.鰓 杷 数3～4+8～ fishes of the Indo-Australian Archipelago, III. 9=11～12を 示 すS.stejnegeriと 明 ら か に 区 別 さ れ る.他 方 両 種 は,吻 ・口 部 の 基 本 的 構 成,背 ・臀 鰭 の E. J. Brill, Leiden: i•`xv, 1•`239, figs. 1•`98. 不 分 枝 軟 条 の 性 状,各 列 の 鱗 数,咽 頭 粛 の 形 状 と 配 (The Institute for Breeding Research, Tokyo 列,脊 椎 骨 数,体 各 部 の 主 要 計 測 形 質 に お い'て ほ とん University of Agriculture, 4-28, Kamiyoga-2, ど 完 全 に 一 致 し て い る.こ の 類 似 性 は,両 種 が 密 接 な Setagaya, Tokyo, 158, Japan) 類 縁 関 係 に あ る こ と を 明 白 に 示 し て お り,ま た,本 新 種 がScaphognathops属 に 帰 属 す る と 判 定 す る に 十 分 ラ オ ス 域 メ コ ン 河 系 か ら 得 ら れ た コ イ 科 で あ る と考 え ら れ る. Scaphognathops属 の1新 種 Scaphognathops属 の コ イ 科 内 に お け る 系 統 ・分 類 ラ オ ス 域 内 の メ コ ン 河 と そ の 支 流 か ら得 ら れ た コ イ 学 的 位 置 に つ い て は い ま だ 不 明 な 点 が 多 い が,吻 ・ 口 科 の1新 種Scaphognathops mekongensisを 記 載 し 部 お よ び 背 鰭 不 分 枝 軟 条 の 性 状 に お け る 類 似 性 か ら み た.Scaphognathops属 は,や や 鋭 利 な角 質 縁 を 形 成 て,東 南 ア ジ ア 産 のScaphiodonichthys属 と類 縁 性 を し 中 央 部 に 下 唇 を 欠 く 下 顎,棘 状 で 鋸 歯 を 有 す る 背 鰭 も つ も の と 考 え ら れ る の 主 不 分 枝 軟 条,棘 状 で 平 滑 な 臀 鰭 の 主 不 分 枝 軟 条 な ど に よ り特 徴 づ け られ,従 来 同 属 に は,同 じ く メ コ ン (158,東 京 都 世 田 谷 区 上 用 賀2-4-28東 京 農 業 大 学 水 系 か ら 報 告 さ れ て い るS.stejnegeri1種 の み が 知 育 種 学 研 究 所)

―136―