Issues of ecological and economical sustainability of fish culture in the southern hydrological basin of lake Balaton

Lake Balaton - as the biggest natural lake in Centr al Europe - has an extended drainage basin (5180 km 2 ). In the southern part of this basin 235 water bod ies can be found, most of them (220) are used as fish ponds while the rema ining serve for angling (15) and for water storage (1). The aim of this study was survey ing this vulnerable area from the main viewpoints of sustainability. GIS based survey of the area revealed that update of the official database is highly recommended, moreov er a significant part of ponds is already covered by macrovegetation. Generally appli ed semi-intensive pond fish culture is based on use of large quantities of organic matt er input (cereal grains and manure) which does not cause environmental pollution during the growing season. Moderate water pollution may occur only in the autumn harves ting time however the almost total use of water sources may negatively influence the w ater balance of the Lake Balaton. Feeding 2 ‐ 3 t/ha cereals per growing season makes possible to obtain net yields around 600 kg/ha in fish ponds. This form of produc tion is not sustainable for long neither from economic nor from environmental point of views. However one part of fish production serves restocking purposes (common carp and carnivorous species) which is indispensable for the management of Lake Balaton th e presence of grass carp, silver carp and bighead carp in the production structure m ay be interpreted as constant hazard for the ichthyofauna of the lake.