Abstract
Nucleolar organizer regions (NORs) polymorphism, constitutive heterochromatin and chromosomal analysis of Moonlight gourami, Trichopodus microlepis in Thailand were firstly reported. Specimens were collected from the Chao Phraya and Mekong Basins, Thailand. The mitotic chromosomes were directly prepared from kidney tissues of ten males and ten females. Conventional staining, Ag-NOR banding and C- banding techniques were applied to stain the chromosomes. The results shown that the diploid chromosome number of T. microlepis was 2n=46 and the fundamental number (NF) was 46 in both males and females. The karyotype consisted of 46 telocentric chromosomes classifying as 14 large and 32 medium. No heteromorphic sex chromosome was observed in T. microlepis. The results also exhibited that the interstitial nucleolar organizer regions (NORs) were clearly observed at the long arm of the chromosome pair 7. This is the first report on NORs polymorphism in T. microlepis that a heteromorphic NOR type in one female had a single NOR-bearing chromosome of the chromosome pair 7, whereas 10 males and nine females had two NOR-bearing chromosomes of the chromosome pair 7 with a homomorphic NOR type. Constitutive heterochromatins located at all centromeres of all chromosome pairs. The karyotype formula of T. microlepis is 2n (46) = Lt14 + Mt32.
Highlights
Trichopodus which was formerly included in Trichogaster (Peapke, 2009; Töpfer and Schlindler, 2009) is a genus of tropical freshwater labyrinth fish of the gourami or family Osphronemidae and subfamily Trichogastrinae found in Southeast Asia
It differs from the most species of the genus Trichogaster (T. labiosa, T. fasciata, T. labiosus, T. sumatranus) which had 2n=48 (Kaur and Srivastava 1965, Calton and Denton 1974, Abe 1975, Rishi 1975, Manna and Prasad 1977, Tripathy and Das 1981, KorefSantibanez and Paepke 1994, Rishi et al 1994, Sobita and Bhagirath 2007, Kushwaha et al 2008) (Table 1)
T. microlepis including all species of the genus Trichopodus have all monoarm chromosomes in karyotype whereas most species of the genus Trichogaster display both mono- arm and bi-arm chromosomes (Table 1)
Summary
Trichopodus which was formerly included in Trichogaster (Peapke, 2009; Töpfer and Schlindler, 2009) is a genus of tropical freshwater labyrinth fish of the gourami or family Osphronemidae and subfamily Trichogastrinae found in Southeast Asia. Constitutive heterochromatin distributions on the chromosomes were widely studied in some fish groups (Brinn et al 2004, Vicari et al 2006, Mesquita et al 2008, Takai 2012). First report on Nucleolar Organizer Regions polymorphism and constitutive heterochromatin of Trichopodus microlepis
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