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7 - Fisheries3.2.4 Habitat degradationThe Government of Viet Nam has identified1.8 million hectares of water surface suitablefor aquaculture. 145 However, freshwater andcoastal aquatic resources are under threat fromenvironmental degradation, over-exploitationand poor management practices. 146Construction of large prawn ponds in Viet Namand failed harvests caused by disease hasresulted in indebtedness. An estimated 75percent of the mangroves and 95 percent ofthe Melaleuca forests have been destroyed inViet Nam, 147 although only a small part of thisfisheries habitat loss is attributable toaquaculture developments.Flooded forests are crucial habitat for fish3.2.5 DiseaseTo date, the epizootic ulcerative syndrome (EUS) in the 1980s has been the only large-scale fishdisease outbreak in freshwater aquaculture in the region. However, it is likely that such problemswill increase in future with further expansion and intensification of aquaculture. Prawn aquaculturein the Mekong Delta has recently been plagued by major disease outbreaks. Intensive cage culturein the Mekong and Bassac Rivers, and in reservoirs in central Viet Nam, have suffered losses of fishduring the past five years. Low-level health problems are known to be a constraint in small-scalepond culture.The infection of humans from liver flukes (trematodes) is a serious health concern in parts of theMekong Basin where raw fish is consumed. 148 Aquaculture can be a means to reduce infection oftrematodes, though it may also be a source of infection. In Lao PDR, trematode infection of wildfish occurs where rivers, streams and paddies are used as latrines. Ponds with over-hung latrines inthe Mekong Delta (a practice which is actually illegal) are still a major source of cultured fish, andalso a possible source of infection for humans. However, the risk factors and management strategiesrelating to these issues require further research.3.2.6 Extension servicesAquaculture extension systems are well developed in Thailand, less so in Viet Nam, and quitelimited in Cambodia and Lao PDR. Within government agencies, there has been a tendency tofocus on peri-urban aquaculture (due to accessibility, private entrepreneur involvement, betteravailability of inputs and access to markets). Focusing government support on small-scale aquacultureand poorer rural households will provide a necessary balance to more commercially-orientedaquaculture. However, this has to be supported by skills development. 149125