Browsing by Author "Alemu, Azene"

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    Chromosome Studies of Fish Species From Lake Tana, Ethiopia
    (Addis Ababa University, 2008-07) Alemu, Azene; Dagne, Kifle (PhD)
    Chromosome numbers are reported here for six species of three genera of Cyprinidae and one species of Cichlidae. Three of the species Labeobarbus nedgia, Labeobarbus. brevicepalus and Labeobarbus intermedius are endemic to Ethiopia and Barbus humilis, Barbus pleurogramma, Garra dembecha and Oreochromis niloticus are native to Ethiopia. Chromosome preparation were made after colchicine injection in proportion to body size (0.5% of 0.8 ml/100 gm) and the fish were placed in aquarium for about 6-8 hours to arrest mitotic chromosomes at metaphase stage. Then the specimens were sacrificed and the gill filament were removed and kept in hypertonic solution (0.75 M KCl), after about 30 minutes the gills were fixed (3:1 methanol- acetic acid). Part of them were preserved for the other time and part of them were taken to grinding dish for crushing with glass rods by adding few drops of fixative. The cell suspensions that were made by grinding of the gill filament were filtered by gauze and centrifuged for 5 minutes (1000 rpm) followed by splash slide preparation. Chromosomes were stained with Geimsa and mounted well. The following 2n chromosomes were observed for the studied seven species: Labeobarbus nedgia, 2n= 150, Labeobarbus brevicephalus, 2n=150, Labeobarbus intermidus, 2n=150, B. humilis, 2n=50, B. pleurogramma, 2n=50, Garra dembeccha, 2n=50 and Oreochromis niloticus, 2n=44. The chromosome numbers were determined from somatic mitotic chromosomes at metaphase stage. Polyploidy is evident in some of the species. Variable basic chromosome numbers were observed from the small and large Barbus fishes. Detailed studies of chromosome morphology were not possible because of the smaller size and large number of the chromosomes. Note on the taxonomy and distribution of each of the genera and species under study are provided. It was recommended that futher cytogenetical studies of the many species occurring in Lake Tana, Ethiopia are required for better understanding of the phylogenetic and evolutionary relationships of the species. Key words: chromosome; Labeobarbus; Barbus; Garra; Oreochromis; Lake Tana;and phylogenetic