Population genetic structure in penaeid prawns

Genetic data are available for 27 species of penaeid prawn. Collected largely for fisheries purposes, they include information on several species of importance to aquaculture. Most studies used allozymes, but a small number have used mtDNA, random amplified polymorphic DNAs (RAPDs) and/or microsatellites. The DNA-based markers have revealed far greater levels of variation compared with the allozyme data. However, in the few cases for which joint information is available, the mtDNA and microsatellite information tended to confirm the spatial patterns of variation detected by allozymes. These revealed little genetic variation over long distances (thousands of kilometres) for many species, but relatively major shifts in gene, or genotype, frequencies over relatively short distances (hundreds of kilometres). Much of the genetic structure in wild populations appears to reflect historical events on large biogeographical scales, rather than resulting from patterns of present-day dispersal. Genetic variation in cultured stocks is generally less than in wild ones, the extent of the reduction being dependent upon broodstock management procedures. There is no conclusive evidence that aquaculture escapees have altered the genetic constitution of wild stocks of Penaeus monodon in Thailand. Nevertheless, the occurrence of strong patterns of geographic variation in wild stocks suggests that more detailed planning will be required to maintain this diversity, and to determine how best to capture its benefits for aquaculture.