Abstract:
This study assessed the variation in the morphological features as a first step in assessing the genetic variability of the fish and later characterizes the fish using cytochrome B and 16S RNA markers to assess the level of genetic variation in the wild populations of Oreochromis niloticus from three locations of South West Nigeria. The pattern of morphological differentiation among Oreochromis niloticus from three populations collected in Ureje river (Ekiti State), Ogbese river (Ondo State) and Asejire dam (Oyo State) were examined using morphometrics and meristics indices. The first principal component (PC1) accounted for 65.80% of the total variance in the sampled populations with characters such as head length (HL) and caudal peduncle length (CPL). The second, third and fourth PCs accounted for 16.18%, 4.14% and 3.31% of the total variation respectively.
The PC loading analysis revealed that Pre-dorsal length (Pre-D) and Pre-pectoral length (Pre-pect) accounted for the 16.18% variation observed in PC 2. The loading on PC 3 revealed snout length (SnL), pre-ventral distance (Pre-V), caudal peduncle length (CPL) and pectoral fin length (PFL) contributed 4.14% variation between the populations of O. niloticus. The fourth principal components showed that the observed differences were mainly from head length (HL), longest anal ray (LAR) and caudal peduncle length (CPL) for morphometric measurements. These regions are important in the description of population characteristics of the fish. Canonical variate analysis (CVA) plot shows overlapping of clusters of specimens for some of the locations studied.
The multiple sequences obtained from the samples showed many nucleotide regions of infractions where major genetic variability occurred in the specimens of Oreochromis niloticus from the three locations. The dissimilarity noticed from the nucleotide bases indicates variation in the genetic pattern of the fish from the different locations. The genetic distance of species between Asejire and Ogbese rivers is 0.368, Asejire and Ureje rivers is 0.212, Ogbese and Ureje river is 0.406 while the genetic distance within the same population of Asejire river is 0.371. The phylogenetic tree constructed revealed that the species are genetically distinct but share a common ancestor or lineage. The study revealed some levels of genetic variability among the species from different populations. This may serve as crucial information for the protection and conservation of the stock to avoid further genetic erosion of the species.
