Aquaculture, Aquarium, Conservation & Legislation International Journal of the Bioflux Society Nutrient reusing capacity of a combined pond aquaculture system

The investigated combined intensive8extensive system (IES) as a production system operated in a close interaction of the intensive and extensive production units. The key element of the proper operation was the treatment capacity of the extensive unit; hence the investigations were focused on the periphyton application on the nutrient utilisation and water quality of the production system. Results proved that combination of intensive aquaculture with extensive fishponds enhances the nutrient utilisation efficiency and fish production in IES. The combined fish production resulted in higher protein utilisation by 26%; even this ratio can be increased by 40% with periphyton application. Introduction . Nutrient retention into fish biomass varies only between 20 and 30% of the introduced fish feed in various aquaculture practices. The combination of intensive fish production with extensive pond culture affords a possible solution to increase the nutrient utilisation of aquaculture. In the frame of the SustainAqua project a pilot scale experiment was implemented in the HAKI in order to investigate the potential of nutrient reusing capacity of combined intensive8extensive aquaculture system (IES) as an integrated aquaculture system. The IES system operated in a close interaction of the intensive and extensive production units. The key element of the proper operation was the treatment capacity of the extensive unit; hence the investigations were focused on the periphyton application on the nutrient utilisation and water quality of the production system. Nutrient retention into fish biomass varies only between 20 and 30% of the introduced fish feed in various aquaculture practices (Hargraves 1998; Brune et al 2003). For the sustainability of aquaculture necessary steps needed to reduce the nutrient input. To make further sustainable increase of aquaculture production possible higher efficiency of nutrient conversion of input nutrients is needed. The fishponds could be an effective tool for water treatment since they are able to retain high amount of nutrients (Knosche et al 2000; Gal et al 2008, 2009). The combination of the intensive fish production with extensive pond culture affords a possible solution for the improvement of the nutrient utilisation and for the diversification of fish species. The overall objective of the IES case study is helping for the traditional carp farmers to use their water more efficiently by producing valuable species in their reservoir or extensively used ponds in order to diversify their production and increase the economical performance of fish production. Material and Method . The experiments of IES were carried out in three ponds (area 310m 2 , depth 1m) served as extensive units, where to a cage was placed as an intensive unit (volume 10m 3 ) in each pond. The ponds were filled up with natural water from a river before a week of fish stocking. The water level was maintained by supplying river water regularly. A paddlewheel aerator (0.5 kW) was applied in the pond to provide sufficient oxygen concentration and maintain the water circulation between the intensive and extensive units (see Figure 1).