Emerging effluent management strategies in marine fish-culture farms located in European coastal wetlands

Abstract

Coastal wetlands are suitable sites for land-based fish culture in ponds and tanks, but environmental constraints on effluent discharges are stringent for these areas. In order to limit effluent loading, different techniques have been proposed and are beginning to be implemented by aquaculturists. On the Atlantic coast of Europe (France, Portugal, Spain, etc.), growout farms for sea bass ( Dicentrarchus labrax), sea bream ( Sparus aurata) or turbot ( Scophthalmus maximus) are often located in wetlands where salt ponds were previously built. Downstream from the rearing ponds, sedimentation ponds are used to reduce particulate matter exportation. Using fish farm effluents, the continuous mass culture of microalgae has been the subject of experiments converting ammonia and phosphates into diatoms, with the systematic addition of required amounts of limiting nutrients (silicon as sodium silicate, or phosphorus as phosphoric acid). New physical treatments may be added if partial recirculation systems are employed, such as immersed foam fractionators, specifically developed for aquaculture ponds. Integrated systems may be emergent practices for reducing the effluent pollutant discharge without additional cost, in addition to producing a complementary income to that resulting from the production of the main culture species.