Evaluation of ozonation on levels of the off-flavor compounds geosmin and 2-methylisoborneol in water and rainbow trout Oncorhynchus mykiss from recirculating aquaculture systems

Common “off-flavors” in fish cultured in recirculating aquaculture systems (RAS) are “earthy” and “musty” due to the presence of the off-flavor metabolites geosmin and 2-methylisoborneol (MIB), respectively. Previously, ozone addition has been applied to RAS at relatively low doses to break refractory organic molecules (i.e., reducing color), microflocculate fine particulate matter (i.e., increasing solids removal), and oxidize nitrite to nitrate, but the effect of ozone addition at these dosing rates on levels of off-flavor compounds was unknown. Ozonation has been used in municipal drinking water facilities to reduce the levels of these compounds, to improve water taste, and to subsequently reduce consumer complaints. In this study, the effects of ozone addition to the inlet water of the RAS culture tanks on levels of geosmin and MIB in the culture water and fish flesh were evaluated. Water and rainbow trout (Oncorhynchus mykiss) samples were obtained twice after maximum feed rates were reached during a 6-month grow-out period. Results indicated that ozone addition to maintain an oxidation reduction potential of 248 mV (<1 μg/L of ozone residual) did not significantly reduce levels of these off-flavor compounds in the water and fish flesh, though it did significantly improve culture tank water quality. Higher dosages of ozone might be beneficial in removing geosmin and MIB in the RAS water, but the inclusion of ultraviolet (UV) irradiation would be required to prevent mortality associated with ozone toxicity.