Effects of ozone in Atlantic salmon post-smolt performance, health and welfare in brackish water RAS

There have been dramatic developments in Atlantic salmon (Salmo salar) farming in the last years. A very striking change is the increased adoption of on-land farming using recirculating aquaculture systems (RAS). In order to maintain superior condition in these systems that require water re-use, water treatment strategies must be adopted. One of the approaches is the use of ozone, a strong oxidant which has been shown to improve water quality and biosecurity; though restricted in freshwater systems. In RAS, ozone inactivates pathogens and reduces organic matter, chemical oxygen demand, dissolved organic carbon, nitrite and water colour. Its use in brackish and seawater systems, however, poses challenges because ozone by-products react with bromide (Br-) that is present in seawater to form hypobromous acid (HOBr) and hypobromite ion/Bromine (BrO-), which are toxic. We have earlier documented the health and welfare impacts of ozone in salmon reared in brackishwater in a flow-through system (FOTS ID 14505). It is yet to be determined the impacts to fish reared in RAS. This trial will investigate the effects of ozone treatment in salmon smolts reared in brackishwater RAS. There will be 2 treatment groups in triplicate, Group A will serve a control while Group B will be the ozone treatment. This group will be subjected to 350 mV of ozone, measured indirectly as oxygen reduction potential (ORP). This concentration was identified to be within the safe limit for salmon based on a previous study (ID 14505). Each group will have 750 fish, distributed in three triplicate tanks (1500 in total; starting average weight 80-100g). The experiment will be carried out over eight weeks. The results of this trial will provide the physiological evidence that will offer insights into the potential use ozone in brackishwater RAS for salmon.