Genetic implications of translocation and stocking of fish species, with particular reference to Western Australia

Species or strains of fish may be translocated for farming, where the only access to the wild is via inadvertent escapes, or for stocking, where delib erate releases are undertaken. In either case, it is important that the tra nslocated animals are representative of the donor population(s) in terms of genetic composition and level of variability. Many studies have shown that this ideal is difficult to achieve, the major reason being the use of inad equate numbers or composition of broodstock as founders of a strain. Also, where more than one conspecific population is involved, there may be outbre eding depression problems. In the case of farming, measures to improve the introduced strain genetically are likely to be undertaken, e.g. breeding pr ogrammes, manipulation of sex and ploidy, transgenic techniques. Such appro aches are necessary economically, but can alter genetic make-up. Thus, stri ngent attempts must be made to minimize escapes or reduce their impact shou ld they occur. With stocking, genetic change during captive rearing should be avoided. No strain manipulation should be undertaken, and other agents o f change should be minimized. Stocking may result in hybridization with rel ated species or with endemic populations of the same species. In either cas e, there can be detrimental genetic effects on the native forms. To be able to identify subsequently any genetic changes in reared strains, whether in tended for farming or stocking, wild population composition should be deter mined, using appropriate molecular techniques. Such molecular methods will demonstrate the degree of interpopulation differentiation and, thus, reprod uctive isolation. The same markers should then be used in each subsequent g eneration (in the hatchery and after escape or reintroduction to the wild) to monitor any changes in genetic composition or variability. Markers shoul d include microsatellite DNA loci, but the inclusion of more than one type of marker is recommended. However, as the aforementioned markers are not co nsidered to be influenced by natural selection, they give no information on the adaptive nature of such differences. For this reason, it is suggested that markers influenced by selection should be investigated. Monitoring a s train subsequent to deliberate or inadvertent release can be undertaken usi ng genetic markers, either deliberately enhanced by breeding or occurring n aturally. Highly variable minisatellite DNA loci have been used as family m arkers in farmed escape studies with Atlantic salmon. These investigations have demonstrated significantly superior survival of native strains compare d with farmed salmon in natural stream conditions. These latter results, de monstrating fitness differences, were strongly indicative of local adaptati on. Thus, methods exist to monitor the genetic effects of translocation and stocking. However, a holistic approach should be taken to such exercises, where genetics forms part of a wider suite of considerations.