Eugnathogobius siamensis ( Fowler, 1934 )

Larson, Helen K., 2009, Review Of The Gobiid Fish Genera Eugnathogobius And Pseudogobiopsis (Gobioidei: Gobiidae: Gobionellinae), With Descriptions Of Three New Species, Raffles Bulletin of Zoology 57 (1), pp. 127-181 : 148-152

Eugnathogobius siamensis ( Fowler, 1934)

( Figs. 17–20 ; Tables 3–6, 11)

Vaimosa siamensis Fowler, 1934: 157 , Fig. 125 (Silom Canal,

Bangkok, Thailand). – Fowler, 1935: 161; Smith 1945: 538,

540–541. Vaimosa mawaia Herre, 1936: 9 , Pl. 6 (Mawai district, Johore,

north of Singapore). – Herre & Myers, 1937: 40; Fowler, 1938:

267; Koumans 1940: 152. Vaimosa jurongensis Herre, 1940: 18 , Pl. 13 (Jurong, Singapore).

– Koumans, 1953: 386–387. Vaimosa oratai Herre, 1940: 20 , Pl. 15 (Brook at Tawau, north

Borneo). – Koumans, 1953: 389. Pseudogobiopsis oligactis – Koumans, 1940: 135. Vaimosa singapurensis – Tweedie, 1940: 75. Stigmatogobius oligactis – Koumans, 1953: 116–117; Suvatti,

1981: 204. Stigmatogobius poicilosoma (in part) – Alfred, 1966: 47. Calamiana siamensis – Hoese, in Böhlke, 1984: 110. Pseudogobiopsis jurongensis – Roberts, 1989: 169–170. Mugilogobius jurongensis – Kottelat, 1989: 19. Mugilogobius mawaia – Kottelat, 1989: 19. Pseudogobiopsis siamensis – Kottelat, 1989: 19; Tan & Tan, 1994:

357; Lim & Larson, 1994: 260; Kottelat & Lim, 1995: 247;

Ng & Tan, 1999: 364; Larson & Lim, 2005: 144; Larson et al., 2008: 143.

Pseudogobiopsis campbellianus – Kottelat et al., 1993: 150, Pl. 70 (in part).

Pseudogobius orotai – Kottelat et al., 1993: 150, Fig. 306.

Pseudogobiopsis wuhanlini Zhong & Chen, 1997: 79–81 (Min River, Fujian Province, China).

Eugnathogobius siamensis – Larson, 2001: 71.

Material examined. – THAILAND: Holotype of Vaimosa siamensis, ANSP 60025, 1(31.5), Silom Canal , Bangkok, R. M. de Schauensee, 18 Dec.1932 . ANSP 87453 , 13 (23.0–32.5), Bangkok, R. de Schauensee, 1936 ; ANSP 63126 , 2 (27.5–28.0), Bangkok, R. de Schauensee, May 1934 . PENINSULAR MALAYSIA: Holotype of Vaimosa mawaia, CAS 29080, 1(24), Mawai district , Johore, A. W. Herre, 22 Mar.1934 . CMK 8485 , 11 (19.0–30.5), blackwater stream, 70 km on road to Kuantan-Pekan-Mersing, Pahang, M. Kottelat et al., 24 Jul.1992 ; ZRC 19323-19324 , 2 (33.5–34.5), stream by Desaru Road, Kota Tinggi , Johor, P. Ng & M. Kottelat, 14 Aug.1991 ; ZRC 17051-6 , 6 (23.5–31.0), freshwater stream on Mawai-Tanjung Sedili Road , Johore, P. Ng & M. Kottelat, 14 Aug.1991 . MALAYSIA, SABAH: Holotype of Vaimosa oratai, CAS 32988, 1(18), Tawau, British North Borneo , A. W. Herre, 17 Jan.1937 . SINGAPORE: Holotype of Vaimosa jurongensis, CAS 32982, 1(36), Jurong, A.W. Herre, 8 May 1937 . Paratypes of Vaimosa jurongensis, CAS 32983, 22(19.5-34), same data as holotype ; BMNH 1938.12.1.215-7, 3(24.5–28.5), same data as previous . BRUNEI: NTM S.14244-001, 8(23.0–28.5), small stream near Kampong Lempong, Temburong Baru, S. Choy, 9 Jan.1992 . INDONESIA: CMK 7304 , 24 (11.5–21.0), tributary of Sungei Siak , Riau Province, Sumatra, M. Kottelat, 13 Feb.1991 .

Other material examined (but not used in description). – CHINA: ZRC 45961, 1 , Lai Chi Wu, New Territories, Hong Kong . THAILAND: USNM 119638 , 37 , Bangpakong River ; USNM 119637 , 23 , Bangpakong River ; USNM 119648 , 29 , Bangkok ; USNM 119650 , 14 , Bangpakong River ; USNM 263426 , 11 , Tale Sap. CAS 53249, 2 , Goh Chang Island , 12°04'30"N 102°22'12"E. PENINSULAR MALAYSIA: CAS 33865, 38 , Kota Tinggi ; CMK 8538 , 38 , Johore ; CMK 7841 , 28 , Johore ; USNM 258941 , 15 , Johore ; USNM 257131 , 53 , Muar River ; CAS 33169, 4 , Mawai , Johore ; CAS 39485, 8 , Kota Tinggi ; USNM 263418 , 5 , Muar River . MALAYSIA: FMNH 51776 , 2 , Sandakan ; FMNH 44932 , 1 , Sandakan , Sabah ; CMK 5683 , 1 , Sungei Sebubut ; NTM S.14240- 002, 8, south of Kuching , Sarawak ; NTM S.14351-002, 4, near Kuching , Sarawak ; ZSM / KEW 495 , 3 , Sungei Stunggang Sarawak . BRUNEI: NTM S.13051-001, 1, Bukit Patoi ; NTM S.14298-001, 5, Temburong . INDONESIA: CMK 7312 , 4 , Sungei Siak , Sumatra ; CMK 9527 , 27 , Sungei Sebuku , Kalimantan Timur , Borneo.

Diagnosis. – A robustly built Eugnathogobius with second dorsal and anal rays always I,6; pectoral rays 16–19; longitudinal scales 22–24; TRB 7-9; predorsal scales 6–8, large, reaching close up to behind eyes; preopercular pores absent, posterior portion of oculoscapular canal absent; scales on body mostly ctenoid; third spine of dorsal fin usually longest, but not elongate; head and body pale with margins of scales outlined in brown, row of brown midlateral blotches, three diagonal dark streaks on head and vertically barred caudal fin; known from China, Thailand and Indo- Malayan Archipelago.

Description. – Based on 36 specimens, 17–36 mm SL. An asterisk indicates counts of holotype of Vaimosa siamensis .

First dorsal VI*; second dorsal rays I,6*; anal rays I,6*, pectoral rays 16–19 (mean 17, 18 in holotype), segmented caudal rays 17*; caudal ray pattern 9/8; branched caudal rays 6/6 to 8/7 (modally 7/7, 8/ 7 in holotype); unsegmented (procurrent) caudal rays 8/7 to 8/8; longitudinal scale count 22–24* (mean 23); TRB 7–9 (mean 8*); predorsal scale count 5–8 (mean 7*); circumpeduncular scales 12*. Gill rakers on outer face of first arch 2+5 to 3+8 (modally 3+7). Pterygiophore formula 3-12210 (in 21). Vertebrae 10+15 (in three), 10+16 (in 29), 10+17 (in one). Neural spines of first few vertebrae slender, pointed (in 11). Two epurals (in 31). Two (in 16) or three (in 15) anal pterygiophores before haemal spine of first caudal vertebra. Scapula unossified. Metapterygoid broad, approximately triangular (apex dorsal), without process extending toward quadrate ( Fig. 17 ).

Body stout, compressed, less so anteriorly. Body relatively stocky, depth at anal fin origin 18.8–23.4% (mean 21.2%) of SL. Head approximately triangular to rounded, depth modally greater than width (or subequal), HL 30.8–34.8% (mean 32.9%) of SL; cheeks may somewhat inflated. Depth at posterior preopercular margin 55.9–69.3% (mean 61.6%) of HL. Width at posterior preopercular margin 58.0–86.0% (mean 70.8%) of HL. Mouth terminal, oblique, forming angle of about 20–25° with body axis; jaws generally reaching to below rear of eye at least in mature males and to below front half of eye in females. Lips usually smooth, fleshy fimbriae may be present on inner edges of upper lip and front of lower lip; lower lip free at sides, narrowly fused across front. Upper jaw 34.2–67.9% (mean 39.0% in females, 54.2% in males) of HL. Eyes dorsolateral, high on head, top forming part of dorsal profile, 21.6–32.7% (mean 27.6%) of HL. Snout slightly pointed, 21.3–35.0% (mean 27.3%) of HL. Interorbital moderate to rather narrow, slightly concave, 10.9–31.6% (mean 16.2%) in HL. Caudal peduncle compressed, length 25.3–31.0% (mean 29.2%) of SL. Caudal peduncle depth 11.4–14.9% (mean 13.1%) of SL.

First dorsal fin low, rounded, second to fourth spines longest or subequal, third spine modally longest; spines longer in males than females; spines barely reaching second dorsal fin origin when depressed in males, spines usually falling well short in females. First dorsal spine always shorter than next three. Second dorsal spine length 13.9–16.9% (mean 16.0%) of SL. Third dorsal spine length 14.0–18.3% (mean 15.6%) of SL. Fourth dorsal spine sometimes longest, in males only, length 14.5–16.1% (mean 15.3%) of SL. Second dorsal and anal fins short-based, posteriormost rays not much longer than anterior rays, rays usually falling well short of caudal fin base when depressed (just reaching in some large males). Pectoral fin slender, pointed, central rays longest, 20.3–29.6% (mean 26.0%) of SL; rays all branched but for uppermost. Pelvic fins long, rounded to oval, reaching to anus, and to anal fin origin in large specimens, 20.7–29.8% (mean 26.0%) of SL. Caudal fin approximately rectangular, rounded posteriorly, 25.0–35.8% (mean 30.0%) of SL.

No mental fraenum, chin usually smooth, sometimes slightly inflated anterior to f papillae row. Anterior nostril in short tube, placed at or just behind preorbital edge, tube oriented down and forward, preorbital sometimes slightly curved to accommodate nostril. Posterior nostril oval, placed halfway between anterior margin of eye and anterior nostril. Gill opening usually extending forward to just under opercle. Inner edge of pectoral girdle smooth with no ridge or flange (in eight); with low bony ridge or flange, sometimes angled outward (in 12); or with low irregular fleshy ridge or knob (in 11). Gill rakers on outer face of first arch very stubby, without spines, longest rakers near angle of arch; rakers on inner face of first arch also short, about equal to longest raker on outer face; outer and inner rakers on other arches same length as inner rakers on first arch. Tongue blunt to concave, occasionally reduced or absent. Outer teeth in upper jaw largest, stout and curved, largest teeth across front of jaw; behind outer row, about three rows of small, curved, sharp teeth; one row of sharp teeth along side of jaw, teeth often absent from rear quarter of jaw in males; teeth slightly smaller in females; tips of teeth may be tinted translucent brownish orange. Lower jaw with about four rows of small curved teeth across front, outermost row oriented upright, inner rows all pointing posteriorly; in males, innermost teeth toward side of jaw large and stout, sometimes three or four teeth strongly curved; teeth absent from posterior half of jaw in males, only one row of teeth at side of jaw in females; tips of teeth may be tinted translucent brownish orange.

Predorsal scales large, evenly sized, reaching forward to behind eyes, anteriormost scale just behind posterior interorbital pore. Operculum with three to five cycloid scales on upper half. Cheek always naked. Pectoral base covered with relatively large cycloid scales. Prepelvic area with small cycloid scales. Belly usually covered with ctenoid scales; some specimens with isolated patch of ctenoid scales under pelvics, rest of scales cycloid; occasionally scales along midline of belly cycloid. Side of body with ctenoid scales extending at least up to behind pectoral base, sometimes extending over top of pectoral base. Anterior scales on sides of body larger than those posteriorly.

Genital papilla in male elongate and flattened, narrowing toward tip; in female, short, rounded and bulbous.

Head pores present. Pair of nasal pores present, pair of anterior interorbital pores (single anterior median pore in one specimen), median posterior interorbital pore, and postorbital pore and infraorbital pore behind each eye. Rear portion of oculoscapular canal absent; preopercular pores absent. Pores often at end of short vertical tubes.

Sensory papillae pattern longitudinal, as in Fig. 18 . Papillae usually quite tall and conspicuous. Cheek rows a, c and cp composed of few large, widely spaced papillae; rows b and d of small, closely spaced papillae. Three s rows on snout, of one papilla each, anteriormost s papilla just behind upper lip, other papillae close together by posterior nostril. Mandibular papillae widely spaced, with mental f row consisting of one papilla on each side of symphysis.

Colouration of fresh material. – From colour slides by Maurice Kottelat. Freshly dead specimens very similar to preserved material. Background colour whitish to greyishwhite with greyish-brown markings on head and body and dark grey to black markings on fins. In some slides, three to five evenly-spaced subcutaneous blackish bars just visible through body wall along lower half of caudal peduncle (three bars) and anal fin base (two bars); usually only three bars along caudal peduncle visible.

Larson & Lim (2005: 144) show a live specimen from Johor, Malaysia, which is generally translucent golden with dusky grey internal blocks of pigment along the lower half of the caudal peduncle and diffuse brown saddles and blotches on the head and body (see description of preserved material). The caudal and dorsal fins are translucent pale yellow, becoming transparent distally, with diffuse grey bands and a blackish spot at the rear of the first dorsal fin. The eyeball is red-brown with pale gold iris.

Colouration of preserved material. – Head and body whitish yellow to pale brownish (depending upon preservation), whitish to pale brown on ventral half, with five narrow brown blotches (resembling short, broad horizontal lines)

along midside of body; scale margins on most of body (not ventrally) narrowly outlined with brown, more diffusely outlined on lower half of body; upper half of body duskier than lower half ( Figs 19 , 20 ). Five diffuse brown saddles sometimes visible, crossing back and reaching down to midside of body toward midlateral blotches. Posteriormost midlateral blotch extending onto caudal fin base and meeting vertical brownish to blackish bar at fin base. Ventral midline of caudal peduncle and along anal fin base with thin black line and (usually) three evenly spaced blackish blotches. Nape plain brownish to whitish-yellow, scale margins broadly outlined with brown, often with indistinct brownish mottling.

Head with three brown markings: first, usually diffuse and indistinct broad bar from front of eye to upper lip (but not extending onto lip); second, broad diffuse streak or patch from lower edge of eye to end of jaw; and third, distinct broad diagonal bar from rear of eye extending backward and ending on middle of cheek, bar often expanded posteriorly; third bar always darkest. Opercle plain brownish or with diffuse brown blotches, usually darker brown irregular marking in centre. Lips and chin plain dusky to brown. Chin and anterior portion of underside of head with scattered dusky spots or plain brownish. Pectoral base with blackish to brown spot or blotch across bases of uppermost few rays. Breast and belly pale to dusky, breast usually darker than belly.

First dorsal fin translucent with two narrow blackish horizontal lines crossing middle of fin, lower line intensified posteriorly as black spot or blotch; broad dusky brown fin margin. Second dorsal fin with four to six rows of brownish to blackish spots, usually coalescing on posterior third of fin at least, forming wavy rows. Anal fin plain dusky to dark greyish brown. Caudal fin translucent to dusky with four to seven vertically oriented, slightly wavy, brownish to blackish lines; anteriormost vertical line thickest and darkest, coalescing with posteriormost midlateral blotch in centre of fin. Pectoral fins with light dusky fin rays, membranes translucent. Pelvic fins plain dusky to brownish, including fraenum.

Comparisons. – This species is most like Pseudogobiopsis oligactis ; see under Comparisons for that species.

Distribution. – Specimens are known from China, Thailand, Malaysia, Singapore, Brunei and Indonesia. It is probably extinct in Bangkok. Ng & Tan (1999) reported the species for the first time from the Endau River system in southern Peninsular Malaysia. This species was thought to be extinct in Singapore until three specimens (ZRC 50271, from MacRitchie Reservoir) were collected in 2005 ( Larson et al. 2008). Eugnathogobius siamensis was not known from China until Zhong & Chen’s (1997) description of Pseudogobiopsis wuhanlini , in which they described material from the Kwangton and Fujian Provinces (Pearl and Min Rivers); and in 1999 ZRC acquired a specimen from the New Territories of Hong Kong.

Ecology. – This species is known only from freshwater habitats, including blackwater streams. It has been found syntopically with P. oligactis .

Adult females are about 10 mm smaller than males. Roberts (1989) briefly discussed maximum size at maturity of this species, comparing specimens from the Kapuas River with the type specimens of Vaimosa jurongensis (from Singapore). He noted that a female from the Kapuas was gravid at 20 mm SL, with “... numerous eggs about 0.20 mm diameter ...”, while three gravid Singapore females were 22.9–24.3 mm SL and had noticeably smaller eggs (0.15 mm diameter) ( Roberts 1989).

Remarks. – Vaimosa oratai Herre, 1940 , was based on two specimens, a large female (holotype at CAS) and a smaller male paratype (13 mm long). The latter has not been examined and its whereabouts are uncertain.

Koumans (1940: 135) considered that Vaimosa siamensis was a synonym of Pseudogobiopsis oligactis , and also observed that Vaimosa mawaia was probably a Pseudogobiopsis ( Koumans 1940: 152) .

Tweedie’s (1940) record of Vaimosa singapurensis from Singapore does not refer to Stigmatogobius borneensis (of which Stigmatogobius singapurensis Bleeker is a junior synonym), but to P. siamensis , as he refers to paratypes from Jurong in the Raffles Museum (which Herre took to CAS/SU). It is possible that V. singapurensis may have been a manuscript name used initially for Vaimosa jurongensis by Herre.

Smith (1945) first noticed the black line and spots along the ventral edge of the caudal peduncle, which are present in this species and P. oligactis , as well as in Pseudogobius and Redigobius . This feature is being investigated further.

Kottelat et al. (1993) combined P. oligactis and P. siamensis under their account of Pseudogobiopsis campbellianus . The specimens in their Fig. 70 are E. siamensis and show the deeper head and barred caudal fin pattern clearly. Upon examination of their preserved material (deposited at CMK), it was found that the specimen lot from which the fish came included both species.

Material of Pseudogobiopsis wuhanlini Zhong & Chen, 1997 , was not available for examination. However, it is clear from the description and illustrations that this is a synonym of E. siamensis . The differences cited by Zhong & Chen fall within the definition of E. siamensis ; they compared it against both P. oligactis and E. siamensis . The statements of “shorter jaw length in adult male, extending only to the vertical line from posterior margin of orbit” (jaws reaching to below rear edge of eye at least in E. siamensis , not to the lower corner of the preopercle in both E. siamensis and P. oligactis as stated by Zhong & Chen); “without the head pore (ρ)” (characteristic of E. siamensis ); and “predorsal scales always 7” (predorsal scales 5–8, mean 7, in E. siamensis ) all agree with E. siamensis . A ZRC specimen from Hong Kong seems to be a typical specimen of E. siamensis .

Figures

Fig. 17. Jaws and suspensorium of Eugnathogobius siamensis, male, ex USNM 119637, Bangpakong River, Thailand. Scale bar = 1 mm.

Fig. 18. Eugnathogobius siamensis, papillae pattern. Paratype, Vaimosa jurongensis, CAS 32983, 33.5 mm SL male, Jurong, Singapore. Scale bar = 1 mm.

Fig. 19. Eugnathogobius siamensis. CMK 7864, 24 and 33 mm SL, Johor, Malaysia. From colour slide by Maurice Kottelat.

Fig. 20. Eugnathogobius siamensis. Holotype of Vaimosa jurongensis Herre, 34.5 mm SL, CAS 32982, Jurong, Malaysia.