Genetic differentiation of fishes in the genera, Clarias and Prophaqorus, in Thailand, using protein electrophoresis and RAPD-PCR

This project was aimed to assess 1) genetic diversity within species of walking catfishes, Clarias macrocephalus, Clarias batrachus and Prophagorus nieuhofii, using isozyme analysis, 2) genetic differentiation between species of walking catfishes of the genera Clarias and Prophagorus using isozyme and RAPD-PCR analyses. Twenty-five natural and one hatchery populations of Clarias macrocephalus were analyzed for thirteen enzymes/protein. Among 18 loci resolved eight loci were polymorphic (P95). Genetic variation within population was low in populations from upper north provinces. It was gradually increased in populations from lower north and upper central provinces. Populations from lower central, north-eastern and southern provinces had low genetic variation within populations. Average heterozygosity, percentage of polymorphic loci and number of alleles per locus were 0.046, 17.12 percent and 1.288 respectively. A hatchery population had high genetic variation (H0=0.06, 27.8 percent polymorphic loci and 1.7 alleles/locus). Population structuring was distinct (Fst=0.162). The natural populations could be genetically separated into 2 groups. Average genetic distance (D) was 0.11+-0.038 (ranged 0-0.04). Eighteen natural populations of Clarias batrachus in Thailand were analyzed for 14 enzyme/protein systems. Fourteen loci out of 22 loci resolved were polymorphic loci and number of alleles per locus across populations were 0.025, 17.6 percent and 1.33 respectively. Population structuring was distinct (Fst=0.545). Two major population groups were identified. Average genetic distance between populations was 0.066+-0.071 (ranged 0.001-0.204). Five natural populations of Prophagorus nieuhofit from southern part of Thailand were analyzed for 10 isozyme/protein systems which resulted in 9 polymorphic loci out of 20 loci resolved. Genetic variation within population was high. (H0=0.041, percentage of polymorphic loci=22.0 percent and number of alleles per locus=1.4). Population structuring was significant (Fst=0.484). Average genetic distance was 0.08+-0.10 (ranged 0.001-0.198). Genetic differentiation among four local species of Clarias catfishes and one introduced species (Clarias gariepinus) was conducted based on analyses of 10 enzyme/protein systems which resulted in 13 loci resolved. Substantial number of diagnostic loci were identified. Genetic distance between species was high and ranged between 0.346 to 1.181. A dendrogram based on Nei (1978) genetic distance separated the 5 species into 3 groups. Cma and Cba, Cme and Cga and Csp. Five out of 40 RAPD primers (OPA-08, -17, OPB-05, 06 and -10) can be used for assessment of genetic diversity of C. macrocephalus, C. batrachus, C. meladerma, C. gariepinus and Prophagorus nieuhofii. Average genetic distance between species was 0.1688 (0.1078-0.2545).