BIODIVERSITAS ISSN: 1412-033X (printed edition) Volume 12, Number 3, July 2011 ISSN: 2085-4722 (electronic) Pages: 141-145 DOI: 10.13057/biodiv/d120304 Morphological divergences among three sympatric populations of Silver Sharkminnow (Cyprinidae: Osteochilus hasseltii C.V.) in West Sumatra DEWI IMELDA ROESMA ♥ , PUTRA SANTOSO Department of Biology, Faculty of Mathematics and Natural Sciences, Andalas University, Padang 25163, West Sumatra, Indonesia. Tel. +62-751- 777427. Fax. +62-751-71343 ♥ e-mail: dewi_roesma@yahoo.com Manuscript received: 22 April 2011. Revision accepted: 17 June 2011. ABSTRACT Roesma DI, Santoso P. 2011. Morphological divergences among three sympatric populations of Silver Sharkminnow (Cyprinidae: Osteochilus hasseltii C.V.) in West Sumatra. Biodiversitas 12: 141-145. Silver sharkminnow (Osteochilus hasseltii C.V.) named by local people as Asang is one of potential Cyprinid fishes species found in several different ecosystems in West Sumatra. The differences of habitat types and another ecological factor among populations may have significant influences on variation and differentiation of morphological characters of this species. In order to elucidate the pattern of morphological divergence, meristic and morphometric characters of O. hasseltii in Singkarak and Dibawah Lake and adjoining river were compared. Phenogram based on cluster analysis showed specific morphological divergence among populations. There were 23 characters significantly different among all compared populations, the highest degree of differentiation was found between Singkarak and Dibawah Lake population (22 characters significantly different) and the most similar population were Singkarak Lake and Ombilin an outlet river of lake (only six characters significantly different). Key words: fish, Osteochilus hasselti, meristic, morphometric. INTRODUCTION Silver sharkminnow (Osteochilus hasseltii C.V) is known as one of widely distributed cyprinids species in many freshwater ecosystems in Sundaland, Indochina, Burma, and introduced to Sulawesi, inhabitant of lakes, river streams and ponds. They could be distinguished morphologically from the other species of the genus by having 12-18 branched dorsal rays; 6-9 rows of spots along scale rows (not always distinct), and a large round blotch on the caudal peduncle, no black midlateral stripe; sometimes with a spot above a pectoral fin (Kottelat et al. 1993). In West Sumatra, O. hasseltii is common cyprinid species in the lakes and rivers, named by local people as Asang Fish. It is frequently catched by fishermen and traded intensively in the traditional markets as potential comodity of freshwater fisheries. Intensive use of small mesh gill nets, electrofishing and dynamite or poisons for catching fishes has given impacts on stability of the number of natural populations for several decades. At least, it has limited the maximum reached size of remaining fishes. There are Singkarak and Dibawah lake as the natural habitat of O.hasseltii among several aquatic ecosystems in West Sumatra. Singkarak is the second largest lake in Sumatra after Toba lake with 107.8 km 2 of surface area and located at 362 m above sea level. The natural outlet is Ombilin river which flows to the Malacca strait. This lake has been experienced by antropogenic polutions continuosly for long period such as organic and anorgnic polutants, pesticides, detergens and another things from people around or run off from the inlet rivers. Naturally, it is connected to Dibawah lake by Batang Lembang river which flows from Dibawah lake into Singkarak. Dibawah lake has 11.2 km 2 of surface area and located at higher altitude than Singkarak (1462 m above sea level) (Lehmusluoto et al. 1997). Differ from Singkarak, Dibawah lake has better quality of water with limited polutant sources. Surroundings area are dominated by farmlands and underbrushes. The fishermen activities are less in compared with Singkarak, make it possible to state that the natural populations of fishes stay in relatively stable. Although Singkarak and Dibawah lakes are included to sympatric category, the differerences in altitude, surface area, and some ecological aspects would be possible forces generate the differences in fish species variation and differentiation living within. These external factors usually have a great influences on species divergence morphologically (Naesje et al. 2004) or ecologically (Fraser et al. 2005). From Mauguit et al. (2010), it was concluded that environmental forces are proposed to be significant strength to form fundamental morphological, physiological and physical changes of fish from hatcling to adulthood. Therefore, in term of some stated reasons, it is evident that there will be a specific pattern on morphological differences among fish populations in Singkarak and Dibawah lakes. This study is aimed to observe the degree of intraspecific diversity of O. hasseltii among those sympatric populations based on morphological characters. These informations are expected to be one of important baseline data in prepararation of biodiversity conservation policies.