Population structure and genetic diversity of Oreochromis shiranus chilwae (Trewavas, 1966) in Lake Chilwa

Lake Chilwa has gone through several water recessions which have adversely affected fishes biomass and species diversity leading to restocking of O. shiranus chilwae at Kachulu in 1969. The study used six microsatellite loci to assess the genetic variability and population structure of O. shiranus chilwae populations and whether the restocked fish radiated to all sites in the lake. The populations exhibited considerably low allelic variability with a total allele number of 58, a mean of 10 alleles per locus and allele number range of 4–18. Observed number of alleles (na), and effective number of alleles (ne) revealed that Chinguma and Chisi were the least and most genetically diverse populations respectively. Based on all allelic diversity indices used in the study, western, northern and southern clusters were not significantly different (p>0.05). The populations in study were discrete, moderately structured (FST=0.12) and not genetically related to each other on the basis of isolation by distance model (Mantels test, r=0.28; p=0.97). Future fish restocking should be done on several sites of the lake because O. shiranus chilwae has low migration rate (Nm=1.8) hence did not radiate to all sites of the lake from Kachulu in 1969. Conservation efforts need to concentrate on each population since the populations are still distinct.