Abstract:
The study investigated genetic variation and relationships among populations of Nile tilapia, Oreochromis niloticus in pond fish farms located in six regions of Ghana. Thirty fish specimens were collected from each farm and analysed together with improved locally bred ‘Akosombo strain’ and imported ‘GIFT-derived strain’ populations. Fin clips of specimens per farm were labelled, put together, preserved in ethanol and transported to CSIR-WRI laboratory for molecular analysis. All samples were screened with five microsatellite markers using Zymo-kit DNA extraction, PCR technology and agarose gel electrophoresis. Bands visualized were scored and analysed using GenALEx, MegaX, and Genpop on the web. Two of the microsatellite markers, GM531 and GM538 showed four alleles per locus whereas UNH154, UNH222, and UNH995 showed three alleles per locus. ‘GIFT- derived’ was highest in heterozygosity at 0.445 whereas locally bred ‘Akosombo Strain’ was 0.232. Heterozygosity was also high in three populations ranging from 0.232 to 0.258 which suggest high variability among the populations. Gene diversity based on locus ranged between 0.180 to 0.430 whereas genetic differentiation between populations (FST) was 0.140 indicating moderate differentiation between the populations. Three fish population clusters were formed; four clustered closely with locally bred ‘Akosombo Strain’, seven clustered closely with ‘GIFT- derived’ and three other fish farms forming a separate cluster. This debunks common perception that O. niloticus farmed in Ghana is solely the Akosombo strain. Cluster of populations also suggested that farmed Nile tilapia populations are now mixed hence production from different farms would not easily be predictable or comparable.
