Stock structure of two important Mekong River carp species (Henicorynchus spp.)

• Mekong River Commission, Fisheries Programme, Cambodia
• Living Aquatic Resources Research Centre, Laos
• Department of Fisheries, Thailand
• Research Institute for Aquaculture No. 2, Vietnam

The Mekong River Basin is home to fisheries that provide food security for approximately 60 million people across several countries. Despite their importance, management of these fisheries is rudimentary at best. The Mekong River Commission (MRC), formed under the cooperation of the four countries sharing the lower parts of the basin (Vietnam, Thailand, Cambodia and Lao PDR) has developed a focus to achieve sustainable fisheries management that will ensure food security is maintained while also factoring in the increasing development pressures on the river.

The Basin offers a wide range of agricultural and industrial development opportunities. Hydro power development is one such opportunity that threatens fisheries, and the river remains an important trade link between the six riparian countries through which it runs. Population increases will continue to put further pressure on the river system and the surrounding environment, as well as on the capabilities of Mekong fisheries.

Management of these fisheries is complicated by the high level of diversity of fish species. Sustainable management practices can vary between species depending on ecology and life histories, and the MRC is studying the ecology and life histories of a number of important fish species. Elsewhere, genetic methodologies have been initiated to identifying discrete gene pools, forming the basis of fisheries management plans, but these technologies have not been used in the Mekong. This project determined whether they were suitable for the Mekong situation.

The major objective of this project was to demonstrate the utility of a molecular genetics approach to stock identification two economically important Mekong River Basin carp species (Henicorynchus siamensis and H. lobatus). The two species were used as models to develop an appreciation of the conceptual basis, data interpretation and application of molecular population genetic analysis to fisheries management in the Mekong River Basin (MRB).

The project team members sampled populations of Henicorynchus siamensis and H. lobatus species at different spatial scales across the natural geographic range in MRB. They used mtDNA genetic markers to document the stock structure. In parallel they developed relevant theoretical and practical training courses in basic genetic and molecular population genetics for regional fisheries. Regional expertise in the interpretation and application of such data sets to fisheries management was also developed.

The two carp species (Henicorhynchus spp.) were targeted for molecular analysis of mtDNA sequences of samples collected from right across the lower Mekong Basin (LMB) with assistance from MRC scientists from the four countries. The study results showed that the two species, while possessing very similar morphologies (often they are confused in the field), had very different demographic histories and most probably will be seen to possess very different ecologies once the studies are conducted. Patterns of genetic diversity were very different in the two species with two discrete stocks identified in the LMB for H. siamensis and three discrete stocks identified for H. lobatus with quite different distributions.

Additional stocks were detected for both species in adjacent drainages, indicating that evolution of genetic diversity in the region in these fishes has been a complex process and probably is related to changes in the paleogeography and river basin evolution of the MRB. These data can provide the foundation for establishing effective management units for fish stock conservation of both species by the MRC. It may be necessary to develop independent management practices for each of these stocks to maintain populations into the future.

In parallel with the genetic diversity studies undertaken at Queensland University of Technology (QUT) for the two model species, a series of training workshops and a Masterclass in microsatellite analysis were conducted for national scientists attached to the project. These provided a foundation to the theory and practice of molecular diagnosis of fish stocks using this approach. In addition, a number of regional scientists received short-course training at QUT and some have commenced or will shortly commence postgraduate degrees that include significant exposure to the genetic technologies employed in the current project. This, in parallel with the development of a new 'state of the art' molecular genetic research facility at Research Institute for Aquaculture No. 2 in Vietnam, means that in the near future the MRC and member countries will have access to both facilities and trained staff. These additions will enable them to commence routine application of the molecular approaches to fish stock identification demonstrated in the current project.