GENETIC DIVERSITY AND POPULATION STRUCTURE OF FOUR TILAPIA FISH SPECIES IN NIGERIA  

Agbebi T. Olubunmi*., Ilori M. Babatunde., Durosaro S. Olutunde., Adegbite  E. Adeola., Ajibade  A. Hammed.,  Adebambo A. Oluwatumininu .,  Adeosun I. Olanrewaju.,  Echefu Joy., and  Ajibike A. Biola
 
Department of Aquaculture and Fisheries Management, Federal University of Agriculture, Abeokuta (FUNAAB), Ogun State, Nigeria. PMB 2240, Abeokuta, Nigeria.
agbebi20@yahoo.com  

Tilapia species belong to the Cichlidae family. Tilapias are divided into three major taxonomic groups based on their reproductive behaviour, substrate incubators (Tilapia spp), maternal mouth brooders (Oreochromis spp), and paternal and bi-parental mouth brooders (Sarotherodon  spp).

Preliminary investigation was carried out on four Tilapia species including; Oreochromis niloticus (ON), Sarotherodon melanotheron (SM), Sarotherodon galileaus (SG), Tillapia zillii (TZ) reared at Eweje farm, FUNAAB reservoir and Opeji farm, all within Ogun State, Nigeria. The study estimated genetic diversity and population structure within this fish species using mtDNA D-loop region. Surprisingly high levels of genetic variability were observed within these species. The SM has the highest number of polymorphic sites while SG has the least. Haplotype diversity for all the species attain unity and implies that all the individuals within each species have accumulated different mutations and are therefore different from each other.  Tajima's D for TZ suggested that the population has experienced a recent, sudden population expansion. Genetic variations within populations accounted for 98.50% and suggested that higher variation existed within population than between populations while 1.50% of the total genetic variation was attributed to that of differences between populations. Two distinct lineages were detected as revealed by Neighbour joining network phylogenetic analysis and revealed that the three populations (ON, SM and SG) probably aggregate into a larger panmictic population and might have descended from a single ancestory lineage. Phylogenetic analysis suggests the existence of two Evolutionarily Significant Units (ESU) within this second lineage.

The result of the study gives way for a better understanding of the behaviour and biology of these species in Nigeria and gives a baseline information for fish management and conservation programs.