Recirculating Aquaculture Systems (RAS) have been used for years in brood stock management and fingerling production and lately increasingly for the on growing phase. RASs are applied because of a number of advantages e.g.: - complete control over environmental parameters; - a significant reduction in water consumption per unit feed input and kg fish produced; - control over the effluent volume and the amount of waste discharge per unit feed input; - effluent treatment (end of the pipeline treatment); - good possibilities for fish health and pathogens control (biosecurity); - prevention of escapees. This session indicated there is a need for research: - into the determination of no effect concentrations (NOEC) of compounds accumulating under RAS conditions. In this session the effect of nitrate6 and carbon dioxide concentrations2 on growth performance were presented. A negative correlation was reported between increasing carbon dioxide concentrations and growth performance in Atlantic salmon post smolts when exposed to CO2-concentrations of 5, 12, 26 , 33 and 40 mg CO2/L (salinity12 ppt, temperature 13°C) in RAS. These results contrast with previous findings in literature where NOEC were reported below 15 mg CO2/L. Maintaining low (< 15 mg/L) carbon dioxide levels has a large impact on the design and economy of RAS. - if effects of water quality parameters in early life have (long) lasting effects in later life of fish, i.e. in this session the effect of CO2 concentrations7 in the hatchery phase on growth performance, health and welfare during the ongrowing phase. - the development of a practical method which indicates in an easy way the required ozone dosage for a particular RAS8. Ozone is applied in RAS as a secondary water treatment step to improve the removal of accumulating fine solids, colloidals, dissolved organic compounds (tea colour), nitrite, bacteria and fish pathogens. In literature the applied ozone refers to a wide range of dosages. Precise dosing of ozone in RAS is important as overdosing can be detrimental for fish health. In this session results were presented on Nitrification, - the effect of feeding method on nitrifying biofilter performance and - the operational and functional comparison of two bioreactor types applied in RAS; Denitrification, - the application of biodegradable plastics as carbon source in a denitrification reactor, - the reuse of carbon from ozone treated sludge for nitrate removal and - nitrate and particulate matter removal in a membrane denitrification reactor; Clear water production, -foam fractionation and ozone treatment for clear water and farm management and - the application of a novel photocatalytic purification system for zebrafish; Species culture in RAS, -culture of Yellow perch in RAS and – effect of stocking density on survival and growth of early juveniles of the Sea Urchin in RAS.
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