Recirculating aquaculture systems (RAS) have been developed for land-based production of sea- and freshwater species. These systems are designed to provide high biomass production while reducing resource usage and maximizing control of operational parameters.

Therefore, Optimizing control and management of water treatment in RAS is of paramount importance as water is renewed at very low rates (≤10%/day). Removal of organic matter, microorganisms and problematic chemical species such as nitrite is performed by applying different steps of filtration, fatty acids or protein skimming, biological treatment and, sometimes, oxidation processes. Among the later, application of ozone has been extensively used as a method to improve water quality to avoid the undesired effect of chemotherapeutants in aquaculture. However, residual ozone can affect various water chemistry parameters (formation of disinfection by-products from halogen anions present in seawater; iodide, chloride and, bromide) and other steps in the water treatment process (mainly biological treatment by disturbing microbial populations in biofilters) with important impacts on fish health and welfare. The OPTIRAS project will tackle this issue in RAS systems, being the main objectives, I- Investigate the changes in water chemical parameters, microbiome and physiology of fish in RAS; II – Develop and deploy online monitoring systems for water chemical parameters relevant for the control of the water quality and the ozone demand; III – Test the adequacy and impact of alternative water treatment processes on fish welfare status and water quality and IV – Demonstrate novel water quality control system in RAS pilots and improved cultivation protocols for diverse fish farming stages and species.