This paper presents the basic operations of an aquaponic prototype and preliminary results on the growth of tench and lettuce. This prototype consisting in a water recirculating system made up of: fish rearing tank with two outlet pipes, one of this connected to a biofilter, NFT hydroponics device and sump; and the other one, to a raft hydroponic device draining to the same sump. Results showed a high survival rate of tenchs (99,32%) and lettuces (98%), and finalization of vegetative cycle of lettuce with commercial sizes, under the following assay conditions: tench stock densities between 0,68 kg/m3 and 1,19 kg/m3, with daily food rates between 0,88 y 1,23% of fishes biomass, a total system water volume of 2,8 m3 and 1,26% of water reposition daily rate, and water variables parameters between 15 and 25ºC temperature; 32 and 105 ppm of nitrate levels; and 8,25 and 7,3 pH values. Control of the above mentioned parameters, plus oxygen levels in water, maintaining fish at low densities and without solids removal devices, reached the optimum regulation system.