Title : IMTA plants Ulva and periphyton and their dual use in reducing N discharge in mariculture effluent and feeding of marine fish
The environmental footprint of mariculture is a major obstacle towards the expansion of this agro-industry. Additional economic constraints are the high costs of effluent treatment and expensive, non-sustainable ingredients in aquafeeds. Biofilters made of Ulva and periphyton differ in their effectiveness in removing ammonia and nitrate from mariculture effluents. The practicality of a combination of these two biofilters in improving the overall removal of dissolved N was evaluated by integrating an Ulva-periphyton biofilter for the treatment of mariculture effluent in an integrated multi-trophic aquaculture system (IMTA).
The paired biofilter resulted in a nearly total depletion of ammonia (97%) and efficient nitrate removal (67%). While Ulva favors uptake of TAN over NO3-N, periphyton reveal no preference between them, with flexible shifts between TAN and NO3-N uptake. Kinetics model of nitrogen removal revealed TAN areal load to determine N uptake rate and efficiency by both the Ulva and periphyton.
The potential of the protein-rich Ulva and periphyton, produced in the biofilter, in feeding of marine fish was further evaluated. When served fresh to fingerlings of the marbled spine-foot Siganus rivulatus, both Ulva and periphyton significantly reduced commercial aquafeeds in diet of this fish.
In other feeding trials, Ulva or periphyton from biofilters was dried, powdered, and integrated into pelleted aquafeeds of the carnivorous sea bream Sparus aurata. Both Ulva and periphyton meals successfully replaced all the expensive fishmeal in the pellets while not harming fish growth performances.