This study describes one possible application of this concept: planted trickling filters adapted to provide nitrification in recirculating systems for fish production. This combination of fish and plant production in an integrated recirculating
system is called aquaponics [7]. Many different system concepts are feasible, depending on the target crops or resources available [8]. Our research focused on the selection of crop plants characterized by high productivity and thus nutrient recycling capacity. To test the suitability of the new combined production system for vegetable producers, we compared plant productivity in aquaponic and in conventional hydroponic systems.