Eugnathogobius polylepis (Wu & Ni, 1985)

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 : 143-148

Eugnathogobius polylepis (Wu & Ni, 1985)

( Figs 14-16 ; Plate 1B,C; Tables 3-6, 10)

Mugilogobius polylepis Wu & Ni, 1985: 95–98 (Zhonggang, Fengxian, Shanghai).

Calamiana polylepis – Larson, in Randall & Lim, 2000: 636; Larson et al., 2008: 141.

? Calamiana polylepis – Larson 2001: 57.

Calamiana sp. nov. 2 – Larson 2001: 61–62.

Material examined. – CHINA: Holotype of Mugilogobius polylepis, SFC S-0001, 31.5 mm SL male, Zhonggang, Fengxian, Shanghai. NSMT P.54851, 1(22), mangrove area, Wenchang, east coast of Hainan Island, K. Matsuura, 10 Mar.1997. TAIWAN: NMMBP-460, 3(22.5–27.0), Tongshu, Charyi County, I-S. Chen, 5 March 1996. VIETNAM: NTM S.16373-001, 2(21.5–24.5), vicinity of Haiphong, North Vietnam, Pham Dinh Trong, Mar.2000. THAILAND: ZRC 50377, 1(19), Laem Phrao, Changwat Trat, Z. Jaafar et al., Feb.2006. SINGAPORE: ZRC 47532, 1(21), Pulau Tekong, N. Sivasothi, 1 Nov.2001; ZRC 50569, 2(20–21), Pasir Ris mangrove, R. Ng et al., 23 Jun.2006. AUSTRALIA, QUEENSLAND: QM I.23883, 2(22.5–24.0), in subsurface mangrove mud, Serpentine Creek, Moreton Bay, 5 Aug.1972; QM I.13374, 3(17.5–21.0), Serpentine Creek, Moreton Bay, CSIRO prawn survey, 7 Nov.1972; AMS I.19580-002, 4(18–26), Serpentine Creek, Moreton Bay, CSIRO prawn survey, 7 Nov.1972; WAM P.28816-001, 3(18–22), Moreton Bay, V. Wadley & P. Young, 7 Nov.1972; WAM P.28814-002, 9(17–23), Moreton Bay, V. Wadley & P. Young, 1972; AMS I.23262-004, 1(20), The Esplanade, Cairns, D. Hoese & D. Rennis, 2 Oct.1982. AUSTRALIA, NORTHERN TERRITORY: NTM S.14236-001, 19.5 mm SL male, among mud and mangrove roots on bank of tidal creek, Reichardt Creek, Darwin Harbour, Northern Territory, R. Hanley, 9 February 1993; NTM S.11933-001, 1(19.5), mud surface, mouth of Adelaide River, R. Hanley, 23 May 1985; NTM S.10419-007, 2(14–19), tiny puddle on mud, East Arm of Darwin Harbour, near Elizabeth River mouth, H. Larson, 29 Mar.1982; NTM S.14075-001, 1(17), on mud surface, Nayarnpi Creek, Roper River, R. Hanley & L. Banks, 7 Sep.1994; NTM S.14074-001, 1(21.5), on mud surface, Nayarnpi Creek, Roper River, R. Hanley & L. Banks, 8 September 1994; NTM S.14080- 001, 1(20), on mud surface, Roper River, R. Hanley & L. Banks, 10 Sep.1994; NTM S.11936-001, 2(18–21), in mud, Rhizophora - lined channel, Little Lucky Creek, McArthur River, R. Hanley, 5 Aug.1985. WESTERN AUSTRALIA: AMS I.25521-007, 1(22.5), Crab Creek, Broome, 0–2 m, D. Hoese & D. Rennis, 20 Sep.1985; AMS I.25523-003, 25(13.5–23.0), King Sound, NE of Derby, 0–1 m, D. Hoese & D. Rennis, 22 Sep.1985.

Other material examined (but not used in description). QUEENSLAND: QM I.13347, 3, Moreton Bay; WAM P.28805- 004, 1, Moreton Bay; AMS I.19580-001, 4, Moreton Bay. NORTHERN TERRITORY: NTM S.14072-001, 1, Roper River; NTM S.14073-001, 1, Roper River; NTM S.14076-001, 1, Roper River; NTM S.14077-001, 1, Roper River; NTM unregistered, 1, Rosie Creek.

Diagnosis. – Small, slender-bodied Eugnathogobius ; first dorsal fin IV-VI, modally V; second dorsal rays I,6–8; anal rays I,7–9; pectoral rays 16–18; longitudinal scales 37–63; TRB 12–22; headpores absent; predorsal scales modally absent, 2–20 small scales may be present on midline before first dorsal fin origin; scales on body small, mostly cycloid, ctenoid scales on caudal peduncle and in small patch under pectoral fin; gill opening restricted to just under opercle; colour pale yellowish with black speckling, black spot on upper caudal fin base in males; known from China, Taiwan, Vietnam, Singapore and northern Australia, in estuarine and mangrove habitats.

Description. – Based on 45 specimens, 14.0– 31.5 mm SL. Counts of holotype ( Fig. 14 ) indicated by asterisk.

First dorsal IV–VI (mean V*); second dorsal I,6–8* (mean I,8); anal I,7–9 (mean I,8*), pectoral rays 16–18* (mean 17), segmented caudal rays 15–17 (mean 16*); caudal ray pattern modally 9/7; branched caudal rays 12–16 (mean 14, 13 in holotype); unsegmented (procurrent) caudal rays 7/6 to 7/8; longitudinal scale count 37–63 (mean 52, 49 in holotype); TRB 12–22 (mean 17, 15 in holotype); predorsal scale count 0–20 (mode 0*, mean 3.8); circumpeduncular scales 13–23 (mean 17, 19 in holotype). Gill rakers on outer face of first arch 2+6 to 4+7 (modally 3+6). Pterygiophore formula 3-12210 in two), 3-112100 (in one), 3-12200 (in one); in first two arrangements, no fin ray attached to last pterygiophore. Vertebrae 10+16 (in six). Neural spine of first few vertebrae narrow, pointed (in five). Two epurals (in five). Two (in four) or one (in one) anal pterygiophores before haemal spine of first caudal vertebra. Metapterygoid broad, with wide bridge overlapping quadrate; palatine slender; pterygoid relatively short.

Body very slender and compressed, less so anteriorly; head relatively broad. Body depth at anal fin origin 12.4–17.1% (mean 14.7%) of SL. Head rounded, always wider than deep, HL 24.5–28.6% (mean 26.4%) of SL. Depth at posterior preopercular margin 49.1–61.0% (mean 54.8%) of HL. Width at posterior preopercular margin 63.9–87.5% (mean 72.1%) of HL. Mouth terminal, slightly oblique, forming angle of about 20° with body axis; jaws not greatly enlarged in mature males, reaching to below anterior half of eye in large adults or to just past anterior margin of eye in specimens less than 20 mm SL. Lips smooth, without fleshy fimbriae present on inner edges of lips; lower lip free at sides, fused across front. Upper jaw 32.7–43.8% (mean 39.1 in males, 36.4% in females) of HL. Eyes relatively small, dorsolateral, high on head, top usually forming part of dorsal profile, 21.7–31.0% (mean 26.1%) of HL. Snout short, flattened, 21.3–31.3% (mean 26.2%) of HL. Interorbital moderate to narrow, flat to slightly convex, 14.0–31.3% (mean 23.4%) of HL. Caudal peduncle very compressed, length 23.5–27.9% (mean 25.9%) of SL. Caudal peduncle depth 10.7–13.6% (mean 12.1%) of SL.

First dorsal fin reduced, low, second or third spines longest or subequal; spines slightly longer in males than females; fin widely separated from second dorsal fin origin. Second dorsal spine length 6.1–11.0% (mean 8.5%) of SL. Third dorsal spine length 6.5–11.0% (mean 8.8%) of SL. Second dorsal and anal fins low, short-based, posteriormost rays longest, rays falling well short of caudal fin base when depressed, only reaching about half length of caudal peduncle. Pectoral fin broad, round, central rays longest, 17.0–22.8% (mean 19.6%) of SL; rays usually all branched (uppermost ray may be unbranched). Pelvic fins short, often cup-like, oval, reaching about one-third to half distance to anus, 12.5–16.3% (mean 14.5%) of SL. Caudal fin short, rounded to truncate, 19.1–25.2% (mean 22.0%) of SL.

No mental fraenum or fold, chin smooth. Anterior nostril tubular, placed at edge of upper lip, tube short, oriented down and forward, preorbital curved to accommodate nostril. Posterior nostril small, rounded to oval, placed very close to upper front margin of eye. Gill opening usually extending forward to just under opercle. Inner edge of pectoral girdle smooth with very low, bony ridge on anterior face of cleithrum, usually forming distinct thin flange of bone, bent laterally. Gill rakers on outer face of first arch very short and unspined, longest rakers near angle of arch; rakers on inner face of first arch stubby with tiny pointed papillae resembling spines; inner rakers on other arches similar in form and length to first arch inner rakers. Tongue tip blunt, occasionally slightly concave. Outer teeth across front of upper jaw largest, sharp and curved; behind this row, two to three rows of very small, pointed teeth; one or two rows of small pointed teeth at side of jaw (teeth similar in males and females). Lower jaw with three or four rows of small pointed teeth across front, outermost row teeth oriented nearly upright, inner rows all pointing inward; usually one or two rows of teeth at side of jaw.

Predorsal scales usually absent, if present, very small, cycloid, mostly along midline just before first dorsal fin, occasionally an additional isolated patch of a few scales or a single row along midline nearly to behind eyes. Operculum naked or with patch of small cycloid scales on upper third to half; sometimes only few scales present. Cheek always naked. Pectoral base naked. Prepelvic area naked. Belly naked, or with midline naked and remaining scales cycloid, or naked anteriorly at least under pelvic fins and with cycloid scales posteriorly. Scales on body small, those on caudal peduncle larger. Most of body scales cycloid; ctenoid scales on side of body usually limited to posterior part of caudal peduncle and small patch behind pectoral fin; ctenii relatively stout, especially on caudal peduncle scales.

Genital papilla in male short, slender and flattened, with pointed tip; genital papilla in female short, rounded and bulbous.

Head pores absent.

Sensory papillae pattern longitudinal, as in Fig. 15 . Two or three s rows present on snout, of one papilla each. Cheek rows b and d composed of small closely spaced papillae; rows a, c and cp of few large widely spaced papillae. Mental f rows of two pairs of papillae.

No swim bladder. Gut simple “S-bend”, with one loop; intestine looping to left rather than right, tucked behind rest of gut as in E. variegatus .

Colouration of fresh material. – Freshly collected specimens from the Northern Territory were noted in field log by the author as being similar to preserved specimens in colour. Colour photographs of live male and female specimens from Singapore and Taiwan were made available by H. H. Tan and I-S. Chen respectively (Plate 1B, C).

Head and body translucent yellowish grey, with scale margins on upper half of body narrowly outlined with light brown, upper half of body with brown to red-brown small spots, cross-hatched blotches, short bars and X-shaped marks; markings may extend below mid-side of body on caudal peduncle; most conspicuous mark in males being dark brown to black, round spot on upper caudal fin base ( Fig. 4 , Plate 1B); in females, spot smaller ( Fig. 16 ). Adult male from Singapore (Plate 1B) almost plain yellowish grey in colour, slightly darker dorsally, with almost no redbrown spots or bars visible; very fine brown cross-hatched markings visible; bright yellow stripe along lower part of body extending from yellow pectoral fin base to just above rear insertion of anal fin.

Head and nape speckled with red-brown to grey-brown dorsally. Side of head with short brown oblique streak extending diagonally from lower rear edge of eye, ending anterior to preopercular edge; short blotchy brown to blackish slightly oblique streak just ventral to eye and ending below posterior margin of eye; a narrow dark brown to red-brown narrow stripe commencing just above rictus and running horizontally along side of head to mid-opercle, extending horizontally onto opercle and ending as indistinct brown blotch; lowermost brown line on head narrow and less distinct than others, beginning below rictus and running just above lower preopercular margin. Upper lip concolourous with snout or bright yellow (in live male from Singapore); lower lip outlined by distinct orange-red to dark pink line ending at rictus. Pectoral fin base with short brown horizontal bar crossing dorsal half, ending on lower pectoral fin ray bases; male with yellow bar across bases of fin rays.

First dorsal fin transparent with lower third of fin dusky to translucent brownish; broad yellow margin to fin in male. Second dorsal fin transparent to translucent yellowish. Anal fin transparent to yellowish brown with diffuse brownish submarginal band in male.

Caudal fin in female transparent, spotted with brown, especially toward base of fin; in male, caudal fin translucent yellow with broad dusky brown submarginal edging, transparent yellowish margin around entire fin, distinct blackish rounded spot on upper base of fin. Pectoral fins transparent, rays silvery-whitish ventrally.

A photograph by Gianluca Polgar of a captive specimen from Sulawesi shows the typical male caudal fin colour but there are no stripes on the head as in other specimens of this species (but this is possibly an artefact of captivity).

Colouration of preserved material. – Head and body light yellow to yellowish grey, with scale margins on upper half of body narrowly outlined with light brown; side of body with small spots, cross-hatched blotches, short bars and X-shaped marks; most conspicuous mark in males being dark brown to black, round spot on upper caudal fin base; in females, spot smaller, light brown and not always distinguishable from other body markings.

Head and nape speckled with pale brown dorsally, pigment evenly distributed or forming pairs of faint spots or two to three narrow bands crossing nape. Side of head with four short brown streaks, central two often diffused into single dark patch: uppermost (first) forming line extending diagonally from lower rear edge of eye and ending before preopercular edge; second streak short, blotchy, extending diagonally from ventral edge of eye to centre of cheek and intersecting mid-point of third streak; third beginning just above rictus, extending horizontally onto opercle and ending as indistinct brown blotch; fourth (lowermost) streak narrow, beginning below rictus and running just above lower preopercular margin. Lips pale whitish yellow, may be light brown (extension of third cheek streak). Underside of head pale with diffuse brownish band crossing isthmus behind chin, band joining anterior ends of lowermost cheek streak. Side of body with two rows of 11–13 short, staggered, cross-hatched brownish blotches or bars; lower third of body mostly pale. Breast brown, distinctly darker than rest of underside. Pectoral base pale with short brown horizontal bar across upper half. Belly whitish, even in heavily pigmented males. Peritoneum brown dorsally, fading on sides toward pale belly.

First dorsal fin transparent to light brown, lower half dusky to brown; or with outer third of fin translucent, central light brown stripe, and lower third of fin translucent whitish. Second dorsal fin light brownish with transparent outer margin, or with scattered pale brown pigment, some forming blotches. Anal fin translucent yellowish brown to brownish, with transparent margin. Caudal fin in females and juveniles translucent yellowish, faintly spotted with brown; in males, caudal fin dusky brown with broad transparent margin around entire fin, dark brown edge separating transparent margin from dusky centre, and distinct dark brown to blackish round spot on upper base of fin, just touching hypural crease. Pectoral fins with light brown fin rays, darkest in males. Pelvic fins light to dark brown, darkest in males.

Comparisons. – This species is close to E. stictos , new species; as stated above, these two grouped together in cladistic analyses ( Figs. 1 , 2 ) and they do not resemble the other Eugnathogobius species. They are small, slender fish characterised by a reduction in dorsal fin spines (usually having four or five spines) and a high number of lateral scales (37 to 63). They appear to be more similar to E. indicus than to other species of Eugnathogobius .

Distribution. – Specimens are known from China, Taiwan, Vietnam, Singapore and northern Australia (from Broome in Western Australia to Moreton Bay in Queensland); possibly also from West Malaysia (see Remarks) and Sulawesi (see Colouration of fresh material).

Ecology. – Eugnathogobius polylepis is usually found in mangroves, at sites not far from the sea. Much of the Queensland material was collected during beam trawl sampling in shallow water. In the Northern Territory, many of the specimens were collected by hand at low tide on mangrove mud-banks, in tiny puddles, on the exposed mud surface or partly buried in the mud. A specimen from Rosie Creek in the Gulf of Carpentaria, was found alive among the bases of dead mangroves Bruguiera exaristata on quite dry, firm mud.

Remarks. – Mugilogobius polylepis Wu & Ni, 1985 , was described from three specimens: the 34 mm SL holotype (SFC S-0001), and two paratypes 22–23 mm SL (SFC S-0002, SFC S-0003). The paratypes now appear to be lost in the postal system (Wu Han-Ling, pers. comm.). My initial impression from Wu & Ni’s illustration (which shows predorsal scales) and the English abstract given in the Plate 1.

A. Eugnathogobius kabilia . Captive males exhibiting agonistic behaviour. Photograph by Hans Horsthemke. B. Eugnathogobius polylepis , captive male, ZRC 50569, 21 mm SL, Pasir Ris, Singapore. Photograph by Heok Hui Tan. C. Eugnathogobius polylepis , freshly dead female specimen, NMMBP-460, Tongshu, Taiwan. Photograph by I-Shiung Chen. original description, was that Mugilogobius polylepis greatly resembled in colour pattern specimens originally identified as Calamiana ( Larson 2001; and originally considered to be a new species: Calamiana sp. nov. 2 of Larson (2001)) from northern Australia, but M. polylepis had VI first dorsal spines (vs. IV–VI, modally V) and more predorsal scales (25–34 vs. 0–16). However, after being able to examine the holotype of Mugilogobius polylepis (brought to Taiwan by Wu), it was found to be a Eugnathogobius almost identical to the northern Australian specimens, but it possessed VI first dorsal fn spines. Specimens from Taiwan and China (Hainan Island) agreed with the holotype of E. polylepis in having the nape naked, and in having VI first dorsal fin spines. However, two specimens from North Vietnam have first dorsal IV–V and 4–5 predorsal scales. Material from Singapore and Thailand have V–VI first dorsal fin spines and 9–20 predorsal scales. All Australian specimens have IV–VI first dorsal fin spines (strongly modally V) and 0–16 predorsal scales (strongly modally 0). No consistent colour pattern or other difference could be discerned (for example, the Singapore and Taiwan populations both have the distinctive orange-red lower lip margin). It is difficult to make meaningful comparisons of the differences in predorsal scale counts and number of first dorsal fin spines (e.g. to determine if there is clinal variation or actually several species involved), as there are 54 northern Australian specimens available, but only 11 from all the South-east Asian localities. So I have retained them all together under E. polylepis , pending further material becoming available.

However, there may be undescribed species related to E. polylepis . For example, several specimens (held at NTM) from mangroves at Sementa, Klang, on the west coast of Peninsular Malaysia, resemble this species but males do not have the dark caudal fin spot. Further collections in appropriate habitat should provide additional specimens which will help clarify their status.

Figures

Fig. 14. Eugnathogobius polylepis. Holotype of Mugilogobius polylepis Wu & Ni, 1985, 31.5 mm SL male, Shanghai Fisheries College S-0001, Zhonggang, Fengxian, Shanghai, China. Photograph by Heok Hui Tan. Specimen has tiny bubbles on dorsal surface.

Fig. 15. Eugnathogobius polylepis, sensory papillae. NTM S.10419-007, Elizabeth River, Northern Territory, Australia. Scale bar = 1 mm.

Fig. 16. Eugnathogobius polylepis, 21 mm SL female, NTM S.14074-001, Nayarnpi Creek, Roper River region, Northern Territory, Australia.

Fig. 4. Eugnathogobius indicus, new species, paratype, 14 mm SL, male, USNM 316139, Grande Terre, Aldabra Atoll, Seychelles.

Fig. 1. Consensus of 10 equally parsimonious trees, resulting from PAUP branch-and-bound search, of Calamiana, Eugnathogobius, Pseudogobiopsis, Pseudogobius and Redigobius (Micropercops and Sineleotris are outgroup).

Fig. 2. One of the 10 trees from PAUP analyses; preferred tree on which classification is based (CI = 0.4935, RI = 0.6929).