Seaweed biofilters as regulators of water quality in integrated fish-seaweed culture units

The water-quality characteristics of a new system for the integrated culture of fish (Sparus aurata L.) and seaweed (Ulva lactuca L.) were examined. Seawater was recirculated between intensive fishponds and seaweed ponds. The seaweed removed most of the ammonia excreted by the fish and oxygenated the water. A model consisting of several tanks and a pilot consisting of two 100-m³, 100-m² ponds were studied. In both, the metabolically dependent water-quality parameters (dissolved oxygen, NH₄⁺-N, oxidized-N, pH and phosphate) remained stable and within safe limits for the fish during over 2 years of operation. The design allowed significant increases in overall water residence time (4.9 days), compared with conventional intensive ponds, and produced a high yield of seaweed in addition to the fish. The design provides a practical solution to major management and environmental problems of land-based mariculture.