Fishes are the most diverse of the major vertebrate groups. However, cytogenetic studiesrnin fish have not been well studied globally as well as here in Ethiopia. Five speciesrnbelonging to four families were sampled randomly from rift valley lakes and some waterrnbodies; and their mitotic chromosomes have been studied or determined using splashingrnmethod. For chromosome preparation, each live fish specimen was injected withrncolchicine (0.5% of 0.8/100 gm body weight) and kept alive for 6-8 hours. The gillrnfilaments were removed and kept in hypotonic solution (0.75M KCL) for about 30rnminutes and then were fixed in 3:1(methanol: glacial acetic acid) for 30 minutes. Gillrnfilaments were grinded with 1-1.5 ml of fixative solution and filtered with gauze. Finallyrnthe cell solution centrifugation for 5 minutes and air-dry slide preparation was made andrnstained in Giemsa. Photographs were taken from the best metaphase plates of eachrnspecimen and chromosome numbers were determined. The result showed that, thernchromosome numbers of (2n) obtained for Tilapia zilli (2n=44), Oreochromis niloticusrn(2n=44), Clarias gariepinus (2n=56), Synodontis schall (2n=54), and Carassius auratusrn(2n= 94) all except the last fish specimen are in agreement with the previous reports.rnSince karyotypic analysis could not be given to all species under the present study, it isrnbetter to carry out further cytological study in the future to get more reliable chromosomerndata for better understanding about their taxonomic and evolutionary relationships.rnKey Words: - Fish, Tilapia, Oreochromis, Clarias, Synodontis, Carassius, diploidrnchromosome number, Rift Valley lakes, Ethiopia.