Nutrient Dynamics of an Aquaponic System in Southern Thailand

Aquaponics is an integrated system of recirculation aquaculture and soilless culture that mainly aims to reduce water requirements, reduce waste discharge and maximize nutrient use. In the present study, an aquaponic system consisting of a 500 L fish tank, sedimentation and pH control tank, degassing tank and three vegetable growing beds was assembled and tested for 17 weeks. Fifty Nile tilapias (Oreochromis niloticus) were reared and fed thrice daily with a complete diet containing 32% protein. Buffer of solid rocks (dead corals) were installed for pH control. Water convolvulus (Ipomoea aquatica) and Tokyo Bekana (Brassica rapa) were rotationally grown at different growth stages. Water samples were collected once a week to analyze pH and NH3/NH4+, NO3-, H2PO4-/HPO42-, SO42-, K, Na, Ca, Mg and Fe concentrations. Fish weight increased from 50 g/fish at the beginning of the experiment to 228 g/fish after 15 weeks. Water pH increased from 6.0 before rearing to 7.0 on the 4th week and varied over the range of 6.9 to 7.0 until the end of the experiment without any additional acid or alkali. Total NH3/NH4+ increased to 10.2 mg-N/L on the 2nd week and rapidly declined to levels below 2.0 mg-N/L. Phosphate, SO42-, Na and Mg accumulated in the system, whereas Ca gradually increased and reached equilibrium at 47±2 mg/L. K and NO2-/NO3- varied considerably at concentrations lower than the general requirement of the vegetables. The first crops of vegetables initially grew well, but growth rates declined remarkably and latter crops showed complex nutrient deficiency. The system could be maintained for 17 weeks without waste discharge.