Population genetic structure of Catla catla (Hamilton) revealed by microsatellite DNA markers

Information on the genetic structure of cultured fish species is essential for optimising fisheries management and stock improvement programs. Eight microsatellite loci (Cc6, Cc7, Cc8, Cc9, Ccat C3, Ccat A12, Ccat G1, and Ccat G2) were analysed to study the genetic variation in three river populations, (the Halda, Jamuna, and Padma rivers) and one hatchery population of Catla catla. Seven of the eight loci analysed were polymorphic in all the populations. Locus Ccat G2 had the highest numbers of alleles (8), while the locus Cc9 had the lowest (2). Differences were observed in heterozygosities and average numbers of alleles among the four populations; however, no difference was observed in proportion of polymorphic loci (P95) among the populations. All the studied populations deviated from Hardy-Weinberg equilibrium proportions at a number of loci, mostly due to the deficiency of heterozygosities. A low level of population differentiation (FST) was observed among populations; however, significant differentiation was evident only between the Halda and hatchery populations. The genetic distance computed by Nei [M. Nei, Genetic distance between populations. Am. Nat. 106, 1972, 283-292.] between the Halda and the other three populations was higher than the genetic distances between all other population pairs. The study revealed a relatively low level of genetic variation at microsatellite loci within and between catla populations, with genetic variation in the hatchery population lower than the river populations. Knowledge of genetic structure of the major river populations and a typical hatchery population is helpful for management of the populations in order to maintain their genetic quality.