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Scleropages inscriptus, a new fish species from the Tananthayi or Tenasserim River basin, Malay Peninsula of Myanmar (Osteoglossidae: Osteoglossiformes).

INTRODUCTION

About ten years ago word reached Bangkok that Scleropages occurs in the Myanmar part of the Malay Peninsula. As Scleropages formosus was well known from the Malaysian part of the peninsula and neighboring areas to the east and southeast, it was assumed that the population in Myanmar was the same species. When Bangkok aquarists saw specimens in the Yangon aquarium trade, however, they recognized immediately that it was an undescribed species with a highly distinctive color pattern unlike anything previously known (Anon., 2011; 2012).

There is a substantial gap in distribution between the known localities for S. formosus in the Malay Peninsula and the Tenasserim or Tananthayi River basin, presently considered the only river system inhabited by the new species. Geographical distribution of S. formosus lies within the area formerly occupied by the Greater Sunda River system and in lowland areas immediately adjacent to it, while the Tenasserim or Tananthayi River system of Myanmar lies outside it and separated from it by low-lying but biogeographically significant mountain ranges.

The holotype and paratype of S. inscriptus, specimens obtained dead from vendors in Meik, are deposited in the fish collection of the Thailand Natural History Museum of the National Science Museum in Pathum Tani. Photographs are presented of the preserved holotype and of a larger live fish not designated as a type specimen.

SYSTEMATICS

Scleropages Gunther 1864

Scleropages Gunther, 1864: 196 (type species Scleropages leichardti Gunther 1864, type locality Burdekin River, Queensland, Australia, by mono-typy and original designation.

Delsmania (subgenus of Scleropages) Fowler, 1934: 243 (type species Osteoglossum formosum Muller & Schlegel 1844, type locality Borneo, Barito River, by monotypy and original designation.

The genus Scleropages was described by Albert Gunther for Scleropages leichhardti Gunther 1864, the first known osteoglossoid fish from the Australian Region. The second known species from the Australian Region is S. jardinii (Saville-Kent 1892).

Henry Weed Fowler distinguished the only previously known Asian species of Scleropages as a subgenus of Scleropages, which he named Delsmania. This taxon has not been generally applied but is available at generic or subgeneric level. The new species S. inscriptus clearly belongs in Delsmania rather than Scleropages. Delsmania differs from Scleropages most obviously in having only 21-24 instead of 31-36 scales in the lateral line series; it also has a less elongate body, longer snout and longer pectoral and pelvic fins (Pouyaud, et al., 2003: 293). The osteoglossid genus most closely related to Scleropages, Osteoglossum, lives in South America. Muller and Henle (1844) originally placed S. formosus in Osteoglossum.

Scleropages formosus (Muller & Schlegel 1844)

Osteoglossum formosum Muller & Schlegel, 1844: 7, pl. 1 (type locality Barito River, Borneo). Scleropages aureus Pouyaud, Sudarto & Teugels, 2003: 298, figs. 10, 11A-B (type locality Pekanbaru market, wild specimen from Siak River, Sumatra, Indonesia).

Scleropages legendrei Pouyaud, Sudarto & Teugels, 2003: 300, figs. 12, 13 A-C (type locality Semitau, area of Sentarum Lake, West Kalimantan, Indonesia).

Scleropages macrocephalus Pouyaud, Sudarto & Teugels, 2003: 296, Figs. 8, 9A-B (type locality Pinoh market, wild specimen from Melawi River, West Kalimantan, Indonesia).

Scleropages inscriptus, n. sp.

Figs 1-2

Holotype: THNHM-F-01521, 385 mm standard length, sex undetermined, supposedly from Myanmar, Tananthayi district, Tananthayi River basin, obtained dead from aquarium fish vendor at Meik, 2011.

Paratype: THNHM-F-01522, 290 mm standard length, sex undetermined, same locality data as holotype.

Diagnosis: Scleropages inscriptus differs from all other Scleropages in having highly distinctive angulated linear markings on dermal bones of circum-orbital and opercular series on sides of head and on scales on sides of body. It differs from the two Australian species of the subgenus Scleropages in meristic and morphometric characters, while at the same time agreeing closely in these characters with its Southeast Asian congener S. formosus of the subgenus Delsmania.

Description: Broad dorsal surface of head and body and scales of predorsal scale row dark, with-out maze-like markings; background color of sides of head and body slightly iridescent, varying from bronze, pearly or pinkish to white or silvery; in fully grown fish dark lines, straight or curved, often joining at right angles, form a maze-like pattern on dermal bones of circumorbital and opercular series and on all scales on sides of body; similar markings on small scales on base of median fins but not on fin rays extending beyond them; pectoral fins with dark rays and pale membranes; pelvic fins pale like background color of body; median fins uniformly dark (not rosy or pinkish); barbels dark dorsally and white ventrally, sometimes with red streak; opening of pupil with red border, eye otherwise dark.

Meristic and morphometrics: The following counts and measurements are from the holotype (and paratype), the only preserved specimens presently available. Measurements are expressed as times in standard length: gill rakers on first gill arch 6+9=15 (6+10=16); pored scales in lateral line scale row 23 (23); median predorsal scales 17 (18); circumferential scales (in front of pelvic fins) 13 (13); circumpeduncular scales 13 (13); peduncular scales (from base of last anal fin ray to end of hypural plate) 9 (9); dorsal fin rays 20 (20); anal fin rays 27 (28); pectoral fin rays 7 (7); pelvic fin rays 5 (5); and caudal fin rays i7+7i (i8+8i); head 3.5 (4.0); snout 16.0 (20.7); horizontal diameter of eye 21.4 (17.1); interorbital width 11.3 (12.1); barbel length 64 (58); greatest depth of body 2.4 (4.0); predorsal length 1.2 (1.3); pre-pelvic length 2.0 (2.1); pre-anal length 1.35 (1.6); depth of caudal peduncle 12.8 (12.6); length of caudal peduncle 21.4 (17.1).

Ontogenetic variation: Young fish up to 200 mm lack maze-like markings on the head and body and have overall silvery or whitish coloration and plain color pattern nearly identical to immature S. formosus which differ mainly in having pinkish or rosy median fins (Pouyaud et al., 2003: figs. 7, 8, 11A, 13C). The distinctive markings of S. inscriptus appear first on the bones of the gill covers at about 200 mm. At progressively larger sizes they extend to the circumorbital bones, the lower jaw, the gill cover membrane, and the scales on the sides of the body. At 300 to about 500 mm the markings cover nearly all of the scales on the sides of the body except the lowermost two rows on the abdomen. Only in specimens of 500-600 mm does the maze-like pattern extend to all of the scales on the body except the darkened uppermost median pre-dorsal row of scales.

Distribution: No precise locality data is available for any specimens of this new species. Thus far it is known only from the aquarium trade in Meik and Yangon. According to a 2006 website posting of the Myanmar fish exporting company Hein Aquarium, the fish comes from the Tananthayi or Tenasserim River basin in Tananthayi district of peninsular Myanmar (Fig. 3). No other localities have been reported.

Etymology: The Latin trivial or species name inscriptus, an adjective meaning "inscribed", refers to the distinctive markings on the scales and facial bones.

Discussion: Sufficient numbers of live specimens of S. inscriptus have been photographed for it to be noted that the maze-like markings are never exactly the same on any two individuals of the species, on both sides of an individual fish, or on any two bones or scales. Nothing quite like this color pattern has been reported in any other osteoglossoid fish or for that matter in any other bony fish.

Overall morphology and nearly identical meristic and morphometric characters indicate that the new species S. inscriptus is most closely related to S. formosus. Based on the information presently available, the three closely related new species or color varieties of Southeast Asian Scleropages proposed by Pouyaud et al. (2003), as recommended by Kottelat and Widjanarti (2005: 145), are not regarded as valid species. Data from partial sequences of DNA coding for cytochrome b and the nearest neighbor dendrogram constructed from it (Pouyaud, et al., 2003: 290-292, table 1, fig. 1) are consistent with the following taxonomic concepts or hypotheses: 1) Scleropages and Delsmania are distinct subgenera; 2) Scleropages leichardti and S. jardinii are distinct species; and 3) Scleropages macrocephalus, S. aureus, and S. legendrei are conspecific with S. formosus.

Having lived in Bangkok for much of the past 40 years, mostly in Sapan Khwai only fifteen minutes walk from the most important Thai tropical fish emporium in Chatuchak Park, I have seen many color variations of S. formosus. All of the so-called arowanas or dragon fish are expensive, but unusually colored ones may fetch ten times or more the price of normally colored ones.

Any aquarist would of course add brine shrimp to fish diets if the fish liked the food and it enhanced their coloration. Hobbyists have been doing this with S. formosus for decades. But commercial dealers reportedly have gone far beyond that, adding to the food artificial colors including, but not limited to, those used to produce the colors of popular soft drinks such as nam daeng, nam kheao, and nam see sohm (red drink, lime green drink, and orange-colored drink) to produce new and more valuable color varieties. Of course this is a trade secret, and my information on such practices is hearsay or inference. The problem is not mentioned by Pouyaud et al. (2003), so perhaps they did not know about it. This presumably has contributed to rejection of their paper by other ichthyologists.

Nothing like this has happened yet with the new species of Scleropages, because too few of them have been marketed and the species probably has yet to be bred in captivity. Bangkok aquarists have succeeded in producing great differences in color pattern in the featherfin Chitala ornata (Osteoglossi-formes, Notopteridae), but this has been achieved by selective breeding. The differences in coloration in S. formosus never involve color pattern, only coloration. Thus the striking differences in color pattern in S. inscriptus strongly indicates that it is not the same species as S. formosus.

Scleropages formosus is distributed extensively in mainland and insular Southeast Asia almost entirely within the geographical area of the former Greater Sunda River basin (Fig. 3). During periods of lower sea level this area was continuous land drained mainly by a single great river system, now represented by several large rivers separated by shallow oceanic gaps including the Mekong, Chao Phraya, Meklong and Tapi on the mainland, Kapuas of western Borneo, and Djambi and Batang Hari of Sumatra. Numerous freshwater fish genera and species are common to this area.

The Tenasserim or Tananthayi River basin of peninsular Myanmar lies outside the area formerly occupied by the Greater Sunda River. Most of its freshwater fish genera and species are shared with the Salween and Irrawaddy river basins of central Myanmar. Only Scleropages and relatively few other genera are shared with Sundaic rivers and not with the Salween or Irrawaddy. S. formosus occurs in the Thai and Malaysian parts of the Malay Peninsula, in which the main river systems are the Tapi and Perak. The Tapi and other river systems of peninsular Thailand are separated from the Tenasserim and other river systems of peninsular Myanmar by mountain ranges that apparently have been a barrier especially for large lowland freshwater fish genera such as Scleropages.

Scleropages inscriptus is one of the most charismatic and attractive of the freshwater fishes endemic to Myanmar. Its continued availability to aquarium fish enthusiasts may depend on successful efforts to cultivate it in captivity. Scleropages formosus has been maintained and successfully bred in varying degrees of captivity and semi-captivity in Thailand, Malaysia and Indonesia for many years. It should be possible to duplicate this success with the new species.

Received: 19 March 2012 - Accepted: 09 April 2012

REFERENCES

ANON. 2011. Aktuelles kurz gemeldet: Ein neuer Arowana aus Myanmar. Amazonas (German edition) 7 (6): 3.

ANON. 2012. Aquatic Notebook: A new arawana from Myanmar. Amazonas (USA edition) 1 (2): 6.

FOWLER, H. W. 1934. Descriptions of new fishes obtained 1907 to 1910, chiefly in the Philippine Islands and adjacent seas. Proceedings of the Academy of Natural Sciences of Philadelphia 85: 233-367.

GUNTHER, A. 1864. On a new generic type of fishes discovered by the late Dr. Leichardt in Queensland. Annals and Magazine of Natural History series 3 14 (81): 195-197, pl. 7.

KOTTELAT, M. & WIDJANARTI, E. 2005. The fishes of Danau Sentarum National Park and the Kapuas Lake Area, Kalimantan Barat, Indonesia. Raffles Bulletin of Zoology Supplement No. 13: 139-173.

MULLER, S. & SCHLEGEL, H. 1844. Beschrijving van een' nieuwen Zoetwater-visch van Borneo, Osteoglossum formosum. Verhandelingen over de natuurlijke geschiednis der Nedertaldsche overzeesche bezittinen, door de Leden der Natuurkundige Commissie in Indies. Leiden, 1-7.

POUYAUD, L., SUDARTO & TEUGELS, G. G. 2003. The different colour varieties of the Asian arowana Scleropages formosus (Osteoglossidae) are distinct species: morphologic and genetic evidences. Cybium 27(4): 287-305.

SAVILLE-KENT, W. 1892. Description of a new species of true Barrimundi, Osteoglossum jardinii, from northern Queensland. Proceedings of the Royal Society of Queensland 8 (3): 105-108.

VIDTHAYANON, C. 2002. Peat Swamp Fishes of Thailand [in Thai and English]. Office of Environmental Policy and Planning, Bangkok, 136 pp.

VIDTHAYANON, C. 2004. Handbook of Freshwater Fishes [in Thai]. Sarakadee Press, Bangkok, 232 pp.

VIDTHAYANON, C., KARNASUTA, J. & NABHITABHATA, J. 1997. Diversity of Freshwater Fishes in Thailand [in Thai]. Office of Environmental Policy and Planning, Bangkok, 102 pp.

Tyson R. Roberts

Smithsonian Tropical Research Institute, Balboa, Panama. E-mail: tysonscleropages@gmail.com
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Author:Roberts, Tyson R.
Publication:aqua: International Journal of Ichthyology
Article Type:Report
Geographic Code:9MYAN
Date:Apr 15, 2012
Words:2230
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