This study used random amplified polymorphic DNA (RAPD) fingerprinting for estimating genetic variation and species differentiation in three species of tilapia. A 16-mer random primer generated RAPD markers ranging from 250 to 2400 base pairs (bp). Genetic similarity estimates obtained by pairwise comparisons based on the method of Nei and Li (1979) indicated high genetic similarity (mean genetic similarity (--_ SD), 0.73 (_ 0.15) for Nile tilapia; 0.78 (_+ 0.12) for Mozambique tilapia; and 0.87 (___ 0.07) for Aureus tilapia) within each of the tilapia species. The average interspecies genetic similarities obtained among the three species were 0.59 (+-0.07) for Mozambique/Nile tilapia, 0.46 (+_ 0.09) for Aureus/Nile tilapia and 0.38 (---0.07) for Aureus/Mozambique tilapia pair. DNA profiles generated in each species of tilapia were unique. A total of 13 RAPD markers differentiating the three species of tilapia were detected. Our study presented RAPD markers as a new class of useful genetic markers for assessment of genetic diversity and species differentiation in tilapia.

Random Amplified Polymorphic DNA (RAPD) fingerprinting offers a rapid and efficient method for generating a new series of DNA markers in fishes. Three oligonucleotide primers (two 10-mers and one 9-mer) and their paired combinations were found to generate different but reproducible RAPD fingerprints in the guppy. Of these, a 10-mer primer (designated S3D2) was used to detect DNA polymorphisms in two guppy varieties, Green Snakeskin (GSS) and 3/4Black (3/4B). High Genetic Similarity (SI) was found among individuals of the GSS and 3/4B varieties indicating low intra-variety genetic variability. The average SI values for the Green Snakeskin and 3/4Black varieties were 0.78 +/- 0.104 and 0.81 +/- 0.083, respectively. The average SI value between individuals of the GSS and 3/4B varieties was 0.66 +/- 0.066, indicating higher genetic variability between the two varieties. To study the inheritance of RAPD markers, single-pair crosses were set up between males of the GSS variety and females of the 3/4B variety. The S3D2 primer was used to generate RAPD fingerprints of the parents and their F1 offsprings. A total of 14 RAPD markers were scored from these crosses. Of these markers, eight (60.0%) of them were polymorphic. The RAPD markers were shown by the F1 to exhibit dominant Mendelian inheritance and could thus be used for subsequent genetic linkage mapping of the guppy.