Solid waste reduction of closed recirculated aquaculture systems by secondary culture of detritivorous organisms

Conventional production systems used in aquaculture such as ponds, raceways, net cages or recirculating systems have in common that they release large amounts of feed nutrients either in dissolved or particulate form. The efficient removal of suspended solids is a key factor for the successful operation of recirculating aquaculture systems (RAS). The here presented thesis utilised the solid wastes from modern aquaculture recirculating system for carnivorous fish for the secondary production of detritivorous organisms (Common ragworm, Nereis diversicolor and European brown shrimp, Crangon crangon). In an experimental integrated recirculating system, fish were cultured for a period of 684 days. During the complete growth period of the fish, polychaete worms were cultivated as exclusive consumer of the excreted particulate waste. The excreted dissolved inorganic nutrients of both fish and polychaetes were utilized either by algae to produce additional harvestable biomass. Water replacement rate during two long term experiments was around 0.8 % / d (system volume). With increasing fish biomass the nutrient and energy supply of the polychaetes could be met to enable them to grow and finally to reproduce. Till the end of the experimental period a self-sustaining worm population up to the fourth generation could be achieved. The growth experiments of the European brown shrimp revealed the potential of the crustacean as detritivorous organisms for integrated aquaculture. The results of this thesis were used for the development of nutrient budget models.