Microsatellite markers reveal genetic degradation in hatchery stocks of Labeo rohita.

The genetic diversity of commercial fishes is devastated due to poor management of broodstock, inbreeding and lack of genetic characterization. Genetic conservation programs are carried out as an effort to recover depleted populations resulting from over-exploitation, environmental fluctuations and natural mortality. Genetic monitoring of a species is essential for the proper management of genetic variability and identification of population groups with independent evolutionary histories. The magnitude of genetic diversity has significant implications for the management and conservation of species. Genetic diversity develops the potential in species and population to maintain and protect themselves against extinction (Ashley et al., 2003), as it provides the basis for survival in ever changing environment (Banerjee et al., 2008). Loss of genetic diversity leads to the fixation of genes, loss of fitness in terms of vigor, fecundity, viability, resistance against diseases and ultimate extinction of local population. Among the carps cultured in Asia, Labeo rohita production was ranked 7th (713267 tonnes) in 2003 (FAO, 2005). Rapid expansion of L. rohita aquaculture has been possible because of the availability of the hatchery produced seed. Currently about 99% of the L. rohita seed originates from private and public hatcheries (Islam and Alam, 2004). Rapid intensification of fry production in hatcheries however, has not been accompanied by genetic quality maintenance measures. In Pakistan, L. rohita aquaculture is suffering from poor genetic management of brood stock. Natural as well as farmed fish populations are facing genetic issues that are quite unique in fisheries management. Anthropogenic intervention is largely responsible for such genetic issues, not only it altered the genetic diversity of fish stocks but also thousands of species and their spawns have been totally destroyed by disruption in breeding and nursing grounds, habitat destruction, overfishing, blockage of migratory routes and various other activities (Collarespereira and Cowx, 2004). On the other hand, indiscriminate genetic hybridization between introduced species, inbreeding due to small breeding population, negative selection, introduction of poor quality hatchery reared seed in wild, species migration in a new habitat and hydrological alteration are some other factors responsible for the loss of genetic diversity among species (Abbas et al., 2010). Unwanted hybridization of L. rohita with C. catla and C. mrigala has been reported as a major problem and partly assumed to be responsible for the decline in growth performance of these species (Simonsen et al., 2004). Introduction of hatchery reared poor quality L. rohita seed to the wild through escapes and government sponsored seed stocking program, often on a massive scale, are becoming a serious concern (Islam and Alam, 2004). It is therefore, imperative to understand the genetic composition of L. rohita stocks in order to ensure their proper management. Pak. J. Agri. Sci., Vol. 52(3), 775-781; 2015 ISSN (Print) 0552-9034, ISSN (Online) 2076-0906 http://www.pakjas. com.pk