Das Projekt "D 7: Research for improved fish nutrition and fish health in upland aquaculture systems in Yen Chau, Son La Province, Northern Vietnam" wird vom Umweltbundesamt gefördert und von Universität Hohenheim, Institut für Tierproduktion in den Tropen und Subtropen (480), Fachgebiet Aquakultur-Systeme und Tierernährung in den Tropen und Subtropen (490i) durchgeführt. Background: Aquaculture significantly contributes to protein supply and cash income of Black Thai farmers in Yen Chau, Son La province, Northern Vietnam. Fish is produced for cash income (2/3rd) and subsistence (1/3rd) while self recruiting species (small fish, crustaceans and molluscs) provide additional protein for home consumption. The current aquaculture system is a polyculture of the macroherbivorous grass carp as main species together with 3-5 other non-herbivorous fish species like Common Carp, Silver Carp, Bighead Carp, Mud Carp, Silver Barb and Nile Tilapia. With a rearing period of 21 months, the productivity of the aquaculture system amounts to 1.54 +- 0.33 t ha-1 a-1 and can be characterized as low. Nearly each household has at least one pond, which serves multiple purposes and is operated as a flow-through-system. The steady water flow is advantageous for the culture of grass carp, but causes a continuous loss of nutrients and high turbidity and thereby limits the development of phytoplankton and zooplankton which are natural food for non-herbivorous species. The farmers are using mainly green leaves (banana, bamboo, cassava, maize and grass) and crop residues (rice bran, rice husk, cassava root peel, distillery residue) as feed input, which is available to Grass Carp while non-herbivorous fish species are not fed specifically. Manure is used as fertilizer. The uneaten parts of fed plants are sometimes accumulating in the pond over several years, resulting in heavy loads of organic matter causing oxygen depletion. Anaerobic sediment and water layers limit the development of zoobenthos and may provide a habitat for anaerobe disease agents. Since 2003 an unknown disease condition has been threatening Grass Carp production and is having a major economic impact on the earnings from fish farming in Yen Chau region. Other fish in the same ponds are not affected. Especially in March-April and in September-October the disease is causing high morbidity and mortalities of Grass Carp in affected ponds and is thereby decreasing the dietary protein supply and income generation of Black Thai farmers. Little is known about the definition or aetiology of the disease condition.