SIMULATION-MODEL OF RECIRCULATING MARICULTURE WITH SEAWEED BIOFILTER - DEVELOPMENT AND EXPERIMENTAL TESTS OF THE MODEL

A simulation model was developed for an experimental recirculating mar iculture system in flat, Israel. The system cultures gilthead seabream (Sparus aurata), using a seaweed biofilter (Ulva lactuca) to maintain water quality, reduce the flow-through rate of seawater, and reduce t he nutrient load in effluents. The model describes the production, tra nsfer, transformations, and losses of inorganic N in the system, in a relatively simple compartment model framework. The model was able to m atch very closely the experimental data on which it is based. Moreover , the model was able to predict the system's behavior in two additiona l experiments, which provided independent tests of the model under non standard operating conditions (reduced food input and reduced water re circulation rate). The success of the model beyond the range of condit ions used in its construction suggests that the model provides a valid mechanistic description of the essential processes affecting inorgani c N in the system. Sensitivity analysis of the model indicates that le vels of ammonia-N and oxidized N in the system were most strongly affe cted by the rates of ammonia-N excretion by the fish and ammonia-N upt ake by the seaweed, followed by the water inflow and recirculation rat es, Sensitivities to internal transformation rate parameters were lowe r, which might explain the relative seasonal constancy of the system. Simulation experiments indicate that the experimental system could sup port much higher stocking densities of fish without exceeding tolerabl e levels of ammonia-N.