Nutrient dynamics in integrated aquaculture–hydroponics systems

Changes in concentrations of dissolved Ca, Cu, Fe, K, Mg, Mn, NO₃-N, Na, P, and Zn, as a function of increasing biomass of Nile tilapia (Oreochromis niloticus) fed a commercial diet in integrated aquaculture–hydroponic systems growing romaine lettuce (Lactuca sativa longifolia cv. Jericho), were monitored over three, 28-day experimental trials. The integrated systems, 320–330 l in volume, were filled initially with a complete nutrient hydroponic solution, and were operated at a 100% recirculation rate. Treatment levels were 0 (control) 151, 377, 902, and 1804 g of fish/system and treatments were conducted in duplicate. Nutrient concentrations and mutual ratios of nutrients quickly departed from initial conditions because the relative proportion of dissolved nutrients excreted by fish and subsequently absorbed by plants differed. The removal of nutrients by lettuce, fish, and solids collection was determined as a function of treatment size. The objective of this study was to quantify both the flow of nutrients through representative integrated aquaculture–hydroponics systems and the effects of different quantities of feed nutrient input on changes in nutrient-specific concentrations.