Redescription of Yirrkala Gjellerupi, a Poorly Known Freshwater Indo- Pacific Snake Eel (Anguilliformes: Ophichthidae)1

By McCosker, John E; Boseto, David; Jenkins, Aaron

Abstract: Yirrkala gjellerupi (Weber & de Beaufort, 1916), unknown since the brief and unfigured original description of the holotype from New Guinea, is herein diagnosed, described, and illustrated, based on specimens recently captured in a Fijian freshwater stream. Other eels collected there and nearby include Anguilla megastoma, A. obscura, Lamnostoma kampeni, and an unidentified moringuid. Living far from the sea is very atypical for an adult ophichthid.

Sphagebranchus gjellerupiwas described by Weber and de Beaufort (1916) on the basis of a 153-mm specimen captured at “Dutch North New Guinea, Tanah Merah in a brook near shore.” This species has not been recorded since its brief and unfigured original description. Tanah Merah (06 140′ S, 140 30′ E) is located on the Digoel River, approximately 200 km from the sea (and a much farther distance by the winding river). Such a habitat is rare for an adult ophichthid eel species, the majority of which live in marine habitats and all of which, as leptocephali, enter the ocean. An extensive ichthyological survey of freshwaters in Fiji by D.B. and A.J. resulted in the capture of four specimens of this rare snake eel, and we herein take the opportunity to provide an expanded description and illustration of this species, as well as information about its habitat.

MATERIALS AND METHODS

Measurements are straight line (point-to-point) and made with dial calipers and recorded to the nearest 0.1 mm. Body length comprises head and trunk lengths; head length is measured from the snout tip to the posterodorsal margin of the gill opening; trunk length is taken from the end of the head to midanus; maximum body depth does not include the median fins. Head pore terminology follows that of McCosker et al. (1989:257). Vertebral counts (which include the hypural) are taken from radiographs. Preanal vertebrae are counted until midanus. The specimens are located in: the California Academy of Sciences (cas), San Francisco; the University of the South Pacific (usp), Suva, Fiji; and the Zoological Museum of Amsterdam (zma), Amsterdam.

TAXONOMY

Yirrkala gjellerupi (Weber & de Beaufort, 1916)

Sphagebranchus gjellerupi: Weber & de Beaufort, 1916:326.

Yirrkala gjellerupi: McCosker, 1977:69.

Figures 1-3

MATERIAL EXAMINED: Holotype, ZMA 104.146, 153 mm (originally described as 152 mm), “Dutch North New Guinea, Tanah Merah” (06 140′ S, 140 30′ E) “in a brook near shore; collected by Dr. K. Gjellerup,” August 1910. USP 5225, 160 mm, Fiji, Viti Levu, Savura River (18 05′ S, 178 26′ E), sampling site no. 13, collected by David Boseto and Sidney Malo, 28 January 2003. CAS 217642, 3 (166- 276 mm), collected 10 m upstream from USP 5225, site no. 14, on 28 January 2003.

DIAGNOSIS: An elongate species of Yirrkala with unique combination of characters: head 6.9-8.6% of total length (TL); tail 56- 58% of TL; dorsal-fin origin in anterior trunk region; rictus of jaw before posterior margin of eye; teeth conical, minute, uniserial on jaws and vomer and absent on intermaxillary; coloration pale, overlain with fine brown punctations above midline; and mean vertebral formula 16-64-154.

DESCRIPTION: Body elongate, its depth at gill openings 36-45 times in TL, tapering posteriorly to an acute, finless point (Figure 1). Body and tail nearly cylindrical throughout, becoming laterally compressed behind midtrunk region. Head and trunk 2.2-2.4 times and head 11.6-14.5 times in TL. Snout acute at tip, conical from above, rounded on underside and split medially. Lower jaw included, its tip reaching slightly behind the anterior nostril edge. Anterior nostril within a tube that extends beyond upper lip, at an angle of approx. 45; posterior nostril within upper lip, its opening beneath center of eye, not visible when mouth is closed. Eye developed, its posterior margin slightly in advance of rictus.

Median fins low but obvious. Dorsal-fin origin about 0.6 head lengths behind gill opening, ending just before tail tip. Gill openings low lateral, their major axis nearly vertical, without an anterior lateral membrane or duplication. Isthmus narrow, slightly wider than gill-opening length.

Cephalic pores (Figure 2) small but discernible, mostly covered with a waxy exudate. Four mandibular, 2 preopercular, 1 ethmoidal + 3 supraorbital, 4 + 2 infraorbital, and single interorbital and supratemporal pores. Lateral-line pores difficult to discern. Largest Fijian specimen has 9 before gill opening, 61 before anal opening, and 133 before ending 22 mm before tail tip.

Teeth (Figure 3) minute, conical, close set, and uniserial. A rosette of 5 anterior intermaxillary teeth, followed by a short gap, then a pair followed by 12-14 uniserial vomerine teeth. Jaw teeth uniserial, approximately 12- 18 in upper jaw and 10-15 in lower.

Body coloration in ethanol pale yellow, with many fine brown punctations, becoming denser above the lateral midline. Ventral surface without spots, except before tail tip. A few brown spots on throat, chin, and snout, forming a thin band between eyes and a broad dark patch across nape. Median fins yellow, unspotted. Cephalic and lateral-line pores unpigmented. Peritoneum pale yellow ventrally, heavily spotted on dorsal surface. Inside of mouth pale.

See Table 1 for counts and proportions of characters of Y. gjellerupi.

REMARKS

This species is remarkable because it ascends freshwater rivers far inland. The holotype was more than 250 river kilometers from the sea, and the Fijian specimens were 10 km from the sea. Water temperature at the Fijian sites was 25.7C, dissolved oxygen was 8.1 mg/ liter, water clarity was about 50%, the current speed was 0.4- 1.2 m/sec, and the stream was 0.74 m deep and 14.2 m wide. The substrate comprised rubble and sand, and the vegetation was primarily moss and paragrass. The sites were 9 and 10 m above sea level.

All three of the cas Fijian specimens appear to be females. The smallest (166 mm standard length [SL]) has minute, undeveloped eggs in each ovary. The larger specimens (229 mm and 276 mm SL) have what appear to be massive, irregularly separated white tissue masses containing either spent or undeveloped ova. (The condition of the tissue disallowed precise microscopic examination, such that their reproductive status could not be discerned conclusively.) The largest specimen appears to have an abnormally enlarged orbit, perhaps associated with breeding condition.

Fijian eels collected along with Y. gjellerupi were the ophichthid Lamnostoma kampeni (Weber & de Beaufort), the anguillids Anguilla megastoma Kaup and A. obscura Gnther, and an as-yet undetermined species of moringuid. The Yirrkala is by far the smallest of those eels, and that it could venture that far upstream seems remarkable.

ACKNOWLEDGMENTS

We thank the following: Isaac Insbrcker and Han Nijssen (ZMA) for loaning the holotype of g jellerupi; the staffs of the California Academy of Sciences and the University of the South Pacific for assistance with specimens; Sidney Malo for assistance with field collections; Beth Heard Guy for preparing Figures 1 and 2; and Tomio Iwamoto and John E. Randall for reading a draft of the manuscript.

1 Manuscript accepted 15 February 2006.

Literature Cited

McCosker, J. E. 1977. The osteology, classification, and relationships of the eel family Ophichthidae. Proc. Calif. Acad. Sci. ser. 4, 41 (1): 1-123.

McCosker, J. E., E. B. Bhlke, and J. E. Bhlke. 1989. Family Ophichthidae. Pages 254-412 in Fishes of the western North Atlantic, Part 9, Vol. 1: Orders Anguilliformes and Saccopharyngiformes. Sears Foundation for Marine Research, Yale University, New Haven, Connecticut.

Weber, M., and L. F. de Beaufort. 1916. Fishes of the Indo- Australian Archipelago. Vol. 3. Ostarophysi: II Cyprinoidea, Apodes, Synbranchi. E. J. Brill, Leiden. 455 pp.

John E. McCosker,2 David Boseto,3 and Aaron Jenkins4

2 California Academy of Sciences, San Francisco, California 94118- 4599 (e-mail: jmccosker@calacademy.org).

3 Institute of Applied Sciences, University of the South Pacific, Laucala Campus, Suva, Fiji Islands.

4 Wetlands International-Oceania, Fiji Office, P.O. Box S6, Superfresh, Tamavua, Suva, Fiji Islands.

Copyright University Press of Hawaii Jan 2007

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