Complete diallel hybridization and molecular characterization of two strains of Oreochromis spp (Makurdi and Swansea strains) was carried out to determine genetic distances, phylogeny of pure strains and their hybrids. Four crosses, namely ?exotic O. niloticus × ?exotic O. niloticus (Treatment 1), ?local O. niloticus × ?local O. niloticus (Treatment 2), ?exotic O. niloticus × ?local O. niloticus (Treatment 3) and ?local O. niloticus × ?exotic O. niloticus. (Treatment 4) were made. Eight 1×1×1m3 hapa was constructed and placed in a concrete tank of 5×5×1.2m3 dimension. Broodstocks of the different crosses were sexed and stocked in ratio 1 male: 2 females in the hapas to spawn. Twenty (20) fry were collected from each cross and their weight and length were taken. The fry was reared for 14 weeks in the indoor hatchery of University of Agriculture, Makurdi, situated at the north core in eight bowls of 55 litres each. Fry were fed ad libitum. Fecundity, Hatchability, Gonadosomatic Index (GSI) and Hepatosomatic Index (HSI) of pure lines were determined. Physicochemical parameters (Dissolved Oxygen, Temperature and pH) of water were measured fortnightly using multi-channel water parameters checker. DNA was extracted from pectoral fin of F1 generation of the crosses. Forward and reverse primers (VF 5’-GTAAAACGACGGCCAGTCAACCACAAAGACATTGGCA-3’; R 5’-CAGGAAACAGCTATGACACTTCAGGGTGACCGAAGAATCAGAA-3’) were synthesized to target and amplified the COI gene. The gene sequences were analyzed independently using Maximum Likelihood (ML) and Pairwise distance methods. Kimura-2 Parameter and phylogenetic tree was constructed using Neighborhood Joining of MEGA 7.0.2 at 1000 bootstrap. Genomic DNA was successfully extracted from all the treatments and COI sequenced with the primers designed. The gene sequence was aligned and edited using BioEdit software. Treatments 1 and 3 of the same maternal origin had the highest DNA weight of 710 bp. The DNA sequences for the four treatments were deposited in GenBank at National Center for Biotechnology Information (NCBI) with Accession numbers MK130700, MK130701, MK130702 and MK130703 for treatments 1, 2, 3, and 4 respectively using the bankit format. When Basic Local Alignment Search Tool (BLAST) was used on the gene sequences of the four treatments, treatments 2 and 4 had 99% identity with O. aureus inferring they have maternal origin linked to O. aureus rather than the originally thought O. niloticus. The phylogenetic tree revealed monophyly with two sub-clades at 95% bootstrap, treatments 1 and 3 of the same maternal origin of exotic strain clustered, while treatments 2 and 4 of same maternal origin (local strain) clustered at a separate sub-clade(Table 1). Treatment 3 had the best performance in terms of growth (4.6g), heterosis (45.97) and survival (82.7%). The result of statistical analyses shows that there is significant difference in growth and length between the different crosses (P<0.05)(Table 2). Treatment 3 is recommended for culture due to overall best performance. From the results of laboratory experiment, it is concluded that O. niloticus populations obtained from university farm were really O. aureus. All the crosses in the four treatments bred through, confirming the possibility of hybridization among the species, thus intraspecific hybridization also was found to be advantageous as maternal inheritance from the exotic female confers hybrid vigor on local strain (Table 3).
Growth performance was monitored and F1 hybrid with the best heterosis was recommended for culture.