In recirculating aquaculture systems (RAS),particulates (including feces, uneaten feed, bacteria, and algae) can cause several problems, in that they may harbor pathogens, can physically irritatethe fish, and upon decomposition, release ammonia and consume oxygen.Mechanical filters, foam fractionators, and other engineered devices are usedto remove particles quickly from aquaculture systems, in order to improve fishhealth and decrease the load on biofilters and oxygenators. Ozone is used inRAS as a disinfectant, to remove organic carbon, and also to remove turbidity,algae, color, odor and taste. Ozone can effectively inactivate a range ofbacterial, viral, fungal and protozoan fish pathogens. But the effectiveness of ozone treatment depends on ozone concentration, length of ozone exposure(contact time), pathogen loads and levels of organic matter. In spite of ozone is a very effective oxidizing agent, higher ozone concentrations are a risk to cultured fish stocks causing gross tissue damage and stock mortalities, and also are a risk to bacterial films on the biofilter.