Genomes of selected wild and cultured populations of Oreochromis niloticus from New Bussa and Ikorodu were comparatively assessed in this study. This was with a view to determining whether certain important genetic principles are being monitored in the cultivation of the fish species and also in the selection of broodstocks in the respective farms.
Twenty specimens of O. niloticus were obtained from the Kainji Lake and Usman farms at New Bussa, Niger State and also Majidun River and Toga farms at Lagos state. Twenty six morphometric characters and 9 meristic counts were taken on each specimen. The morphometric and meristic data were subjected to principal component analysis (PCA). DNA samples were extracted from caudal fin clips of the fishes using Cetyltrimethylammonium bromide (CTAB) based procedure. The purified DNA was analysed in a Multigene Gradient thermocycler using 8 microsatellite markers. The amplicons generated were subjected to fluorescent genotyping and the corresponding allele scored. The data obtained were used to determine genetic parameters such as inbreeding coefficient, observed and expected heterozygosity, allelic richness, effective number of allele and Nei genetic distance.
The average expected heterozygosities for Kainji Lake, Usman farms, Majidun River and Toga farms were 0.7488, 0.7043, 0.5953 and 0.4533, respectively. The heterozygousities of the two populations from the wild deviated from Hardy-Weinberg equilibrium (HWE) while the heterozygosities of the cultured populations were within HWE. On the average, three populations (Kainji Lake, Usman farms and Majidun River) were inbred while one population (Toga farms) was outbred. The analysis of genetic distance among the populations showed two major clusters. One cluster comprised Kainji Lake and Usman farms while the second cluster comprised Majidun River and Toga farms. However, Kainji Lake and Usman farms were significantly differentiated while Majidun River and Toga farms were weakly differentiated using morphometric characters. The wild populations largely overlapped while the cultured populations were significantly differentiated. The measures of differentiation by morphometric characters were found to be different from molecular characters.
The study concluded that the wild population of Oreochromis niloticus from New Bussa was a suitable source of Nile Tilapia broodstocks for aquaculture.