RESUMO
An investigation of gill monogeneans from the Nile tilapia Oreochromis niloticus and the blue spotted tilapia Oreochromis leucostictus (50 individuals per species) was done between the months of November 2014 to February 2015 in Lake Naivasha, Kenya. Standard parasitological procedures were used to examine fish gills for the presence of monogeneans. The observed monogeneans were collected, preliminarily identified using identification keys, quantified and fixed in 4 % formalin for morphological studies and absolute ethanol for molecular studies. Four parasite species comprising of three species of the genus Cichlidogyrus and one species of the genus Scutogyrus were recovered. Cichlidogyrus sclerosus and Cichlidogyrus tilapiae infested both fish species but the C. sclerosus was most prevalent in O. leucostictus (Prevalence (P) = 100 %, Mean intensity (MI) = 3.4) and C. tilapiae in O. niloticus (P = 8 %, MI = 4). Cichlidogyrus tilapiae had a P = 12 % and MI = 5.0 and a P = 6 % and MI = 3.0 in O. niloticus and O. leucostictus, respectively. Cichlidogyrus halli (P = 4 %, MI = 15.5) and Scutogyrus gravivaginus (P = 2 %, MI = 1.0) were only found in O. leucostictus. This is the first time that these monogeneans have been identified from Lake Naivasha, Kenya, presenting new geographical records. It was concluded that Ancyrocephalids (Cichilidogyrus spp.) dominated the two cichlid fish species in Lake Naivasha, Kenya.