COSMOS, Vol. 6, No. 1 (2010) 91 93 © World Scienti¯c Publishing Company DOI: 10.1142/S0219607710000449 THE ZEBRA SPINY EEL (MACROGNATHUS ZEBRINUS) — A NON-NATIVE SPECIES IN SINGAPORE (SYNBRANCHIFORMES: MASTACEMBELIDAE) HEOK HEE NG Ra®les Museum of Biodiversity Research Department of Biological Sciences National University of Singapore 6 Science Drive 2, #03-01, Singapore 117546 heokhee@nus.edu.sg Received 2 October 2009 Revised 19 February 2010 More information on the distribution of the zebra spiny eel (Macrognathus zebrinus), a non-native species recently recorded in Singapore, is provided in this study. The spiny eel is known from four reservoirs (Kranji, Lower Peirce, Lower Seletar, and Tengeh) on the island. The presence of large numbers of this species in the Kranji and Lower Seletar reservoirs indicates that the zebra spiny eel is now established in Singapore. Keywords: Mastacembeloidei; invasive species; Myanmar; reservoir. 1. Introduction 2. Material and Methods The spiny eels (Mastacembelidae) are a group consisting of about 70 species of eel-like acanthomorph ¯shes found in tropical Africa, Asia Minor and most of southern and eastern Asia.2,6 Among species recognized within the family is the zebra spiny eel, Macrognathus zebrinus (Blyth, 1859), which is native to the Irrawaddy, Salween and Sittang river drainages in Myanmar.10,11 During recent surveys of the aquatic fauna of Singapore's reservoirs conducted under the auspices of the Public Utilities Board (PUB), specimens of Macrognathus zebrinus were captured at four reservoirs in Singapore. This species was recorded as a non-native or alien species in Singapore for the ¯rst time by Baker and Lim,1 but without any information as to its distribution and biology. The purpose of this article is to furnish such details. The ¯sh were collected using a combination of gill nets and small traps, and euthanized on ice and ¯xed in formalin before being transferred to 70% ethanol for long-term storage. Measurements were made point to point with a pair of digital calipers and data recorded to tenths of a millimeter; lengths are given as standard length (SL). The material examined in this study is deposited in the Zoological Reference Collection of the Ra®les Museum of Biodiversity Research, Singapore (ZRC). 2.1. Material examined ZRC 50883, 5 ex., 36.4 96.0 mm SL; ZRC 51852, 1 ex., 297.5 mm SL; ZRC 51855, 1 ex., 195.9 mm SL, Singapore: Lower Seletar Reservoir. ZRC 51884, 2 ex., 270.8 302.1 mm SL; ZRC 51909, 1 ex., 91 92 H. H. Ng 268.4 mm SL, Singapore: Kranji Reservoir. ZRC 51982, 1 ex., 183.1 mm SL, Singapore: Lower Peirce Reservoir ZRC 52035, 1 ex., 193.0 mm SL, Singapore: Tengeh Reservoir. 2.2. Diagnosis Macrognathus zebrinus can be distinguished from congeners in having a combination of the following9,10: rostrum rounded in cross section and edentulous; rim of the anterior nostril with six ¯nger-like projections; 2 4 preopercular spines; one preorbital spine; 28 31 dorsal ¯n spines; 49 55 dorsal ¯n rays; 51 59 anal ¯n rays; 72 74 vertebrae; dorsal and anal ¯ns separate from caudal ¯ns; sides of the body with 18 22 thin, dark vertical bars with pale outlines; and caudal ¯n vertically striated with small black spots. 3. Discussion The zebra spiny eel has been recorded at four of the 15 reservoirs in Singapore: Kranji, Lower Peirce, Lower Seletar, and Tengeh (Fig. 2). This species is frequently exported as an ornamental ¯sh in the aquarium ¯sh trade,8 and this is surmised to be the most likely route of introduction to the reservoirs. The discarding of aquarium ¯sh is a common pathway by which alien species are introduced into waterways,5 although in the case of the Kranji Reservoir, the close proximity of aquarium ¯sh exporters in the Sungei Tengah Agrotechnology Park, adjacent to the reservoir, may also be a likely source of the introduction. Although the species is reported to reach a size of 250 mm SL,11 the present record shows that it is capable of growing to larger sizes (up to 300 mm SL). Large numbers of the juvenile zebra spiny eel have been encountered in the Lower Seletar Reservoir, indicating that this species is breeding within this reservoir. The juvenile eels appeared to be more numerous when the reservoir was covered with a thick growth of Ceratophyllum demersum (Ceratophyllaceae), Egeria densa (Hydrocharitaceae), E. najas, Hydrilla verticillata (Hydrocharitaceae) and Lagarosiphon major (Hydrocharitaceae) (almost all of it since removed), as the dense beds of aquatic plants seemed to form ideal habitats for the ¯sh to hide in. Although juvenile ¯sh were not obtained from the Kranji Reservoir, the large numbers of adult ¯sh encountered also strongly suggest that this species is breeding and is established in the reservoir. Mastacembelid eels are often overlooked as potentially invasive species, despite the fact that another mastacembelid species, the peacock spiny eel (Macroganthus siamensis), has also been Fig. 1. Macrognathus zebrinus, ZRC 51855, 195.9 mm SL, Singapore: Lower Seletar Reservoir. (Photograph courtesy of H. H. Tan.) Fig. 2. Map of Singapore's reservoirs showing the localities where established populations of Macrognathus zebrinus were found. The Zebra Spiny Eel reported as an established alien species in southern Florida, USA.3 Although Macrognathus siamensis has also been reported from the Upper Seletar Reservoir in Singapore by Ng and Lim,7 it is believed that this species is not established in Singapore, since only one individual was encountered and further surveys have failed to locate the presence of this species in the reservoir. There is one native species of spiny eel, the bu®-backed spiny eel (Macrognathus maculatus), which is nationally critically endangered and known only from a small area of the Central Catchment Nature Reserve.4 As the Lower Seletar Reservoir is physically connected to the streams °owing through the Central Catchment Nature Reserve, the potential danger of the zebra spiny eel as an alien invasive merits further study. Acknowledgments I thank Alvin Lok, Norman Lim and Ting Hui Ng for assistance in ¯eld work, Alvin Lok for identifying the aquatic plants, and Heok Hui Tan for the use of Fig. 1. The PUB is gratefully acknowledged for granting permission to survey the reservoirs and for providing the support necessary for doing so. References 1. Baker N and Lim KKP, Wild Animals of Singapore: A Photographic Guide to Mammals, Reptiles, Amphibians and Freshwater Fishes, Draco and Nature Society (Singapore), 2008. 93 2. Berra TM, Freshwater Fish Distribution, Academic Press, San Diego, 2001. 3. Fuller P, Macrognathus siamensis, USGS Nonindigenous Aquatic Species Database, Gainesville, Florida, 2009. http://nas.er.usgs.gov/queries/FactSheet.asp? speciesID=2261 Revision date: 28 January 2005. 4. Lim KKP, Tan HH and Low JKY, Fishes, in: Davison GWH, Ng PKL and Ho HC (eds.), The Singapore Red Data Book: Threatened Plants and Animals of Singapore, 2nd edn., The Nature Society (Singapore), pp. 213 245, 2008. 5. Lintermans M, Human-assisted dispersal of alien freshwater ¯sh in Australia, NZJ Mar Freshwater Res 38: 481 501, 2004. 6. Nelson JS, Fishes of the World, 4th edn., John Wiley and Sons, New York, 2006. 7. Ng PKL and Lim KKP, The freshwater ¯shes of Singapore, J Singapore Natl Acad Sci 22{24: 109 124, 1996. 8. Riehl R and Baensch HA, Aquarium Atlas, Vol. 3. Mergus Verlag, Melle, 1997. 9. Roberts TR, Systematic review of the Mastacembelidae or spiny eels of Burma and Thailand, with description of two new species of Macrognathus. Jpn J Ichthyol 33: 95 109, 1986. 10. Su¯ SFK, Revision of the Oriental ¯shes of the family Mastacembelidae, Bull Ra®les Museum 27: 93 146, 1956. 11. Vidthayanon C, Termvidchakorn A and Pe M, Inland Fishes of Myanmar, SEAFDEC, Bangkok, 2005.