Allozyme revealed substantial genetic diversity between hatchery stocks of Siamese fighting fish, Betta splendens, in the province of Nakornpathom, Thailand

This study was conducted to quantify genetic variation within and between stocks of hatchery reared Siamese fighting fish, Betta splendens, which is an economically important ornamental fish in Thailand. Our preliminary study showed that a natural population of Siamese fighting fish had average number of alleles/locus of 1.5, 45.5% polymorphic loci and Ho = 0.065. Fourteen stocks of Siamese fighting fish comprising seven populations each of hatcheries with closed and open broodstock management practices were collected from Nakornpathom Province, Thailand. Thirteen isozyme systems and one protein system were analyzed and resulted in 19 loci being resolved that included seven polymorphic loci. Most populations conformed to Hardy-Weinberg equilibrium (P > 0.0002) after Bonferroni correction. Genetic variation within hatchery populations with closed and open systems was not different. All had relatively low average numbers of alleles per locus which were between 1.32-1.42 (averaged 1.38) whereas observed and expected heterozygosities were relatively high (Ho = 0.081-0.125, averaged 0.099; He = 0.091-0.142, averaged 0.113). A high value of Fst (Fst = 0.0754; P < 0.0002) indicated strong population structuring. Average Cavalli-Sforza and Edwards genetic distance was 0.081. The populations were not strongly grouped according to the neighbor-joining tree. It is concluded that sufficient genetic diversity among populations existed although allele diversity and proportion of polymorphic loci were reduced relative to wild population.