Allozyme variation of hatchery and river populations of rohu (Labeo rohita, Hamilton) in Bangladesh

The genetic variations of rohu (Labeo rohita, Hamilton) sampled from five hatchery populations (Arabpur, Brahmaputra, Comilla, Kishorganj and Natore) and three major river populations (the Halda, the Jamuna and the Padma) were analysed by allozyme electrophoresis. Ten enzymes encoded by 11 loci were screened, and six were polymorphic. Alleles at three loci (Est-1(*), Gpi-1(*) and Gpi-2(*)) proved variable for hatchery and river populations, and the Mdh-2(*) locus exhibited heterozygous genotypes for river populations only. Polymorphic loci per population (27.3 +/- 5.3%), heterozygous loci per individual (15.5 +/- 1.2%) and relative gene diversity (0.27 +/- 0.08) in river populations were higher than those for hatchery populations (25.5 +/- 1.8%, 10.7 +/- 1.6% and 0.25 +/- 0.01 respectively). Also, the observed heterozygosity (Ho) and expected heterozygosity (He) (0.09 +/- 0.03 and 0.14 +/- 0.04 respectively) in river populations were higher than those in hatchery populations (0.08 +/- 0.01 and 0.11 +/- 0.01 respectively). The lower levels of genetic variability in hatchery populations suggested the occurrence of inbreeding and/or genetic drift. The pairwise population differentiation (F-ST) values showed a lower level of genetic differentiation between hatchery and river population pairs. The unweighted pair-group method with arithmetic mean dendrogram of Nei's genetic distances showed a relationship between the genetic distance and geographic distance. The populations were clustered into three groups: the Padma in one group, the Halda in second group and the Jamuna, including five hatcheries, in the third group. Highly diversified rohu individuals were observed in the Padma and Halda Rivers, whereas less genetically variable individuals were found in the Jamuna River and five hatcheries. These findings can be useful for rohu hatchery propagation to enhance the sustainable aquaculture production.