© 2009 The Japan Mendel Society Cytologia 74(3): 317–322, 2009
A New Report of Karyotype in the Chevron Snakehead Fish, Channa striata (Channidae, Pisces) from Northeast Thailand
Weerayuth Supiwong, Pornpimol Jearranaiprepame and Alongkoad Tanomtong*
Department of Biology, Faculty of Science, Khon Kaen University, Khon Kaen, Muang 40002, Thailand
Received July 23, 2009; accepted November 14, 2009
Summary The chromosomes of the chevron snakehead fish (Channa striata) from Khon Kaen and Mahasarakam provinces, Northeast Thailand, were investigated by using conventional staining and Ag-NOR staining techniques. The diploid chromosome number of all 2 populations was 2n 42, with karyotype composed of 6 metacentric, 2 acrocentric and 34 telocentric chromosomes, NF 50, without heteromorphic sex chromosomes. This is a new report of karyotype in the C. striata. Ag- NOR was located on region adjacent to the centromere of chromosome pair 14. Here we first demonstrated Ag-NOR bands in snakehead fish from Thailand. In the future, basic knowledge about C. striata and its cytogenetics will be applied to studies of breeding, conservation and chromosome evolution in this fish.
Key words Snakehead fish (Channa striata), Karyotype, Chromosome, Thailand.
The chevron snakehead fish (Channa striata) is a member of the family Channidae which are the native fish in Asia (Thailand, Indonesia) and Africa. Snakeheads are very important in fishery, aquaculture, food fish species, pharmaceutical products and traditional medicine (Ambak et al. 2006). The 2 genera of Channidae are Channa and Parachanna. Channa are the native fish in Asia and Parachanna are endemic in Africa. At present, there are 29 snakeheads species found in the world including 3 species of Parachanna and 26 species of Channa. There are 7 species found in Thailand (Courtenay and Williams 2004, Vidthayanon 2005). There have only been few cytogenetic studies on the Channid fish in Thailand. Six species have been studied cytogenetically, each having a different diploid number: C. marulioides, 2n 38 (Magtoon et al. 2006), C. striata, 2n 44 (Wattanodorn et al. 1985, Donsakul and Magtoon 1991), C. marulius, 2n 44, C. micropeltes, 2n 44, C. lucius, 2n 48 and C. gachua, 2n 112 (Donsakul and Magtoon 1991). However, some species from India and Bangladesh have different diploid number from these studies i.e. C. (2n 40), C. marulius (2n 40) and C. gachua (2n 78) (Nayyar 1966, Banerjee et al. 2003, Ruma et al. 2006). All that we mentioned before the variations on chromosome number and morphology in Thai and Indian snakehead fish. Variations on chromosome number and morphology can be found between different populations of the same species or among different individuals of the same population and even in different cells of the same specimen (Diniz and Bertollo 2006). Furthermore, interpopulational chromosome variation has also been observed in the Erythrinid fish, Hoplerythrinus unitaeniatus (Giuliano-Caetano et al. 2001, Diniz and Bertollo 2003). In this article, we report karyotypes and other chromosomal markers such as the these Ag- stained nucleolar organizer region (Ag-NOR) of C. striata population from Khon Kaen and
* Corresponding author, e-mail: [email protected] 318 W. Supiwong et al. Cytologia 74(3)
Fig. 1. Metaphase chromosome plates of the chevron snakehead fish (Channa striata, 2n 42) from Northeast Thailand by using conventional straining technique (above) and Ag-NOR straining technique (below). The arrows indicate the metacentric chromosomes and the arrow heads show NOR-bearing chromosome (bar 5 micrometres).
Mahasarakam provinces, Northeast Thailand. This study describes the similarities and differences of chromosome among populations. Moreover, we also report the first description in Ag-NOR chromosome of the sneakheads from Thailand. In the future, basic knowledge about C. striata and its cytogenetics will be applied for the studies of breeding, conservation and chromosome evolution in this fish.
Materials and methods Five males and 10 females of C. striata were obtained from local markets in the Khon Kaen and Mahasakam provinces, Northeast Thailand. The fishes were transferred to laboratory aquaria and were kept under standard conditions for 7 d prior to the experiments. The Procedure for fish chromosome preparation by white blood cells culture was modified from Gold et al. (1990) and/or 2009 A New Report of Karyotype in the Chevron Snakehead Fish 319
Fig. 2. Metaphase chromosome plates and karyotypes of male (A) and female (B) chevron snakehead fish (Channa striata, 2n 42) from Northeast Thailand by using conventional staining technique. The arrows indicate the metacentric chromosomes pair 1, 2 and 4 (bar 5 micrometres). 320 W. Supiwong et al. Cytologia 74(3)
Table 1. Mean of length short arm chromosome (Ls), length long arm chromosome (Ll), length total arm chromosome (LT), relative length (RL), centromeric index (CI) and standard deviation (SD) of RL, CI from metaphase chromosomes in 30 cells of the chevron snakehead fish (Channa striata, 2n 42)
Chromosome Ls Ll LT RL S.D. CI S.D. Size Type pairs
1 0.970 1.003 1.973 0.0376 0.0026 0.509 0.006 L m 2 0.851 0.906 1.757 0.0332 0.0018 0.518 0.015 L m 3 0.250 1.296 1.546 0.0299 0.0018 0.843 0.051 L a 4 0.743 0.800 1.543 0.0283 0.0013 0.519 0.017 L m 5 0.000 1.351 1.351 0.0257 0.0011 1 0.000 M t 6 0.000 1.305 1.305 0.0248 0.0011 1 0.000 M t 7 0.000 1.262 1.262 0.0240 0.0011 1 0.000 M t 8 0.000 1.226 1.226 0.0233 0.0009 1 0.000 M t 9 0.000 1.201 1.201 0.0229 0.0008 1 0.000 M t 10 0.000 1.178 1.178 0.0224 0.0006 1 0.000 M t 11 0.000 1.155 1.155 0.0219 0.0005 1 0.000 M t 12 0.000 1.134 1.134 0.0215 0.0005 1 0.000 M t 13 0.000 1.118 1.118 0.0212 0.0005 1 0.000 M t 14 0.000 1.091 1.091 0.0207 0.0007 1 0.000 M t 15 0.000 1.060 1.060 0.0201 0.0008 1 0.000 M t 16 0.000 1.034 1.034 0.0197 0.0009 1 0.000 M t 17 0.000 1.006 1.006 0.0191 0.0010 1 0.000 M t 18 0.000 0.964 0.964 0.0183 0.0011 1 0.000 S t 19 0.000 0.915 0.915 0.0174 0.0011 1 0.000 S t 20 0.000 0.872 0.872 0.0165 0.0013 1 0.000 S t 21 0.000 0.837 0.837 0.0158 0.0014 1 0.000 S t
Remarks: L large chromosome (LT 1.405), M medium chromosome (LT 0.987–1.405), S small chromosome (LT 0.987), m metacentric chromosome, a acrocentric chromosome and t telocentric chromosome. directly prepared kidney cells (Chen and Ebeling 1968, Nanda et al. 1995). The chromosome slides were stained with 10% Giemsa’s for 30min and Ag-NOR sites were identified according to Howell and Black (1980). The metaphase figures were analyzed according to the chromosome classification after Chaiyasut (1989). The centromeric index (CI) between 0.50–0.59, 0.60–0.69, 0.70–0.89 and 0.90–0.99 were described as metacentric, submetasentric, acrocentric and telocentric chromosomes, respectively. The fundamental number, number of chromosome arm or NF, is obtained by assigning a value of 2 to metacentric, submetasentric and acrocentric chromosomes and 1 to telocentric chromosome.
Results and discussion The diploid number (2n) found in C. striata was 42 chromosomes in both sexes. This differs from previous studies by Wattanodorn et al. (1985), Donsakul and Magtoon (1991), Nayyar (1966) and Banerjee et al. (1988). The NF was 50 which agrees with Wattanodorn et al. (1985) and Nayyar (1966) but differs from reports by Donsakul and Magtoon (1991) and Banerjee et al. (1988). The karyotype was composed of 6 metacentric, 2 acrocentric and 34 telocentric chromosomes (Figs. 1, 2). No cytologically distinguishable sex chromosome was observed. In the present study, karyotype of the C. striata among populations was different because of the genetic variation between inter- population of the snakeheads and the difference in the criteria for classification of chromosome type. However, there were some interesting events, the 2 reducing diploid chromosomes while the 2 metacentric chromosomes adding in the genome. For example, Wattanodorn et al. (1985) reported 2n 44 chromosomes including 4 metacentric chromosomes (Central Thailand), whereas this study 2009 A New Report of Karyotype in the Chevron Snakehead Fish 321
(Northeast Thailand) has 2n 42 composing 6 metacentric chromosomes, and Banerjee et al. (1988) found 2n 40 chromosomes with 8 metacentric chromosomes in snakehead fish from India. The variation on chromosomal number was derived from intraspecific Robertsonian translocation (centric fusion) through which 2 telocenric chromosomes fuse becoming to metacentric chromosome. The 2n changes as a result of the translocation, but the NF remains constant. This phenomenon also found in C. asiatica (Channidae). The population from Guangzhou (South Guangdong province) has 2n 46 chromosomes; whereas those from Shashi (Hubei province) and Shaoguan (North of Guangdong province) have 2n 44 chromo- somes. However, these 2 complements share an equal number of chromosomal arms (Yu and Zhou 1996). Moreover, for green sunfish (Lepomis cyanellus), 3 karyotypes were Fig. 3. Idiograms showing lengths and shapes of chromosomes of the chevron snakehead fish detected: 1) 2n 48 telocentric chromosomes; (Channa striata, 2n 42) by using conventional 2) 2n 46 chromosomes (44 telocentric staining technique. chromosomes 2 metacentric chromosomes); 3) 2n 47 chromosomes (46 telocentric chromosomes 1 metacentric chromosome). It was concluded that this variation was due to centric fusions between telocentric chromosomes. Consequently, the derived metacentric chromosome was formed (Beçak et al. 1966). Accordingly, this process plays an important role in small scale evolution in snakehead fish. C. striata displayed terminal Ag-NOR on chromosome pair 14 (Fig. 1). This characteristic differs from C. punctata which has interstitial Ag-NOR in the largest submetacentric chromosome pairs (Sharma et al. 2002, Sahoo et al. 1997). Here we first demonstrated Ag-NOR bands in the snakehead fishes from Thailand. The NOR location can describe the chromosome evolution. Interstitial NOR probably was originated by tandem fusion between NOR-bearing chromosomes and other chromosomes but C. punctata might have been produced NOR-bearing chromosomes through pericentric inversion or even through centric fusion of 2 telocentric chromosomes, one of which had telomeric NOR. (Sharma et al. 2002) The data of the chromosomal checks on mitotic metaphase cells of the chevron snakehead fish are shown in Table 1. Fig. 4 shows the idiogram for the chevron snakehead fish from conventional staining. The karyotype formula for the chevron snakehead fish is as follows:
m a t t 2n(42) L6 L2 M 26 S 8
Acknowledgments This work was financially supported in part by Khon Kaen University’s Graduate Research Fund, Academic Year 2008 (No. 51131105) and Development and Promotion of Science and Technology talents project (DPST). 322 W. Supiwong et al. Cytologia 74(3)
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