GENETIC IMPROVEMENT OPTION AND GROWTH PERFORMANCE OF THREE CULTURABLE TILAPIA SPECIES IN A COASTLINE TIDAL FED POND.  

Morphological, molecular and growth performance differences between three close Cichlid species (Oreochromis niloticus , Sarotherodon melanotheron and Tilapia guinneensis ) were investigated in a south western Nigerian coastline tidal fed pond. This study used both phenotypic (culture and growth) and molecular characterisation (random amplified polymerase DNA (RAPD) and Simple sequence repeat (SSR) techniques to fingerprint the tilapia species from selected water bodies to determine their growth performance and degree of relatedness and to correctly assign them into distinct genetic group for possible genetic improvement options.

The growth performance analysis recorded 100% survival for all population studied and the average daily weight gains (ADWG) of O. niloticus showed the highest (0.51g), while T. guineensis and S. melanotheron have the same ADWG of 0.23g. The S. melanotheron population showed the highest specific growth rate (SGR) of 0.45 followed by the T. guineensis (0.41) and O.niloticus (0.37). There were significant difference in the mean growth of paired T. guinneensis and S. melanotheron (P<0.05) but none for paired of T. guinnensis and O.niloticus; and S.melanotheron and O. niloticus (P< 0.05). The study showed that the three species exhibited positive and negative allometric growth in the tidal fed earthen ponds but S. melanotheron with a condition factor of 1.94 was recorded as the best candidate for the studied environment.

The bands generated from the molecular results showed that the inter-specific similarity coefficient between T. guineensis and S. melanotheron for the wild was 78%; culture was 80%; and 100% for both wild and culture samples. This result further suggests that the SSR loci used in this study were polymorphic and heterogeneity was detected among the genotypes which present an idea for breeding intension. Therefore, the detected microsatellite loci might be recommended for characterizing Tilapia species in Nigerian water bodies. Such information has implications for future broodstock selection and breeding management and for further analysis of interactions between different populations of Tilapia species.