FST-244P Intensive production of fish and shellfish in recirculating aquaculture systems can accumulate particulate organic matter (uneaten feed, feces, microorganisms, etc.) and dissolved organic matter (small organic molecules not visible to the human eye). These suspended solids are irritating to the gills and external tissue of the animals; will degrade in the water, contributing to toxic nitrogen waste; and can harbor pathogenic bacteria and toxic algae. For these reasons mechanical filtration units (settling basins, microscreen filters, foam fractionators, etc.) are critical components of aquaculture systems because these filters are designed to remove particulate matter.