CHROMOSOME ANALYSIS OF WALKING CATFISH, Clarias spp. 61 Malays. Appl. Biol. (2009) 38(1): 61–64 * To whom correspondence should be addressed. CHROMOSOME ANALYSIS OF WALKING CATFISH, Clarias spp. SITI SHAPOR SIRAJ 1 , RATIAH SUKARDI 1 , CHERYL CHEAH PHAIK IMM 1 , KHEW HUAI MEI 1 , SHALINI VELLASAMY 1 , JOTHI MALAR PANANDAM 2 and SITI KHALIJAH DAUD 3 1 Department of Aquaculture, Faculty of Agriculture, 2 Department of Animal Science, Faculty of Agriculture, 3 Department of Biology, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor E-mail: shapor@putra.edu.my ABSTRACT Karyotyping is one of the useful tools for species identification, taxonomy, evolutionary and breeding selection. To date, no information on karyotyping of this fish in the country is documented. The aim of this study was to determine and differentiate the karyotypic structure and fundamental arm number of the walking catfish; Clarias macrocephalus, Clarias batrachus and Clarias gariepinus. The fish samples ranging from 23–160gm in weight and 16–40cm in length were used to obtain the chromosomes by subjecting to a combination of colchicine and phytohaemagglutinin for arresting a mitotic division. The karyotype of each species was arranged according to size, type and structure such as metacentric (M), submetacentric (SM), subtelocentric (ST) and acrocentric/telocentric (A/T). The diploid chromosome numbers ranged from 2n equal to 54 (Clarias macrocephalus and Clarias batrachus) to 2n equal to 56 (Clarias gariepinus). ABSTRAK Kajian kariotip merupakan salah satu kaedah penting untuk pengenalpastian spesies, taksonomi, evolusi dan pemilihan baka. Hingga kini tiada maklumat kariotip ikan ini didokumentasikan di negara. Tujuan kajian adalah untuk menentukan dan membezakan struktur kariotip dan nombor lengan asas ikan keli; Clarias macrocephalus, Clarias batrachus dan Clarias gariepinus. Sampel ikan yang mempunyai julat berat 23–160gm dan julat panjang 16–40cm digunakan untuk memperoleh kromosom melalui suntikan yang mengandungi kolchisina dan fitohemaglutinin bagi menghalang pembahagian mitosis. Kariotip setiap spesies disusun mengikut saiz, jenis dan struktur seperti metasentrik (M), submetasentrik (SM), subtelosentrik (ST) dan akrosentrik/telosentrik (A/T). Bilangan kromosom diploid berjulat di antara 2n = 54 (Clarias macrocephalus dan Clarias batrachus) hingga 2n = 56 (Clarias gariepinus). Key words: Chromosome, Karyotype, Clarias, Walking catfish INTRODUCTION Walking catfish is a large family of catfishes found in freshwater of Africa, Syria, India and Southeast Asia. It is named for its prominent barbells, a cylindrical body, flattened bony head and a broad transverse mouth with four pairs of long barbells around it. It also has an accessory air-breathing organ allowing it to survive in oxygen-poor water or even out of water (Kottelat et al., 1993). These catfishes come in a variety of sizes (lengths range from 10 to 200 cm) and can be distinguished from one another through their occipital process (Mohamed Mohsin and Ambak, 1991). Classified as an omnivore, they feed on a wide variety of prey, including eggs or larvae of other fishes. Cytogenetic studies on fish have been useful in providing information concerning evolutionary and taxanomic studies, as well as for the genetic improvement of commercial fish stocks (Gold, 1979). Karyological and cellular DNA content data are important in understanding the genetic and systematic of fishes (Gold et al., 1980). Although the application of fish karyotype has received a considerable attention in recent years in many parts of the world, there are still a very limited data on karyotype of the endemic fish in Malaysia. The aim of this study was to determine the karyotypic structure of Clarias batrachus, C. macrocephalus and C. gariepinus.