Acute dose-response exposure of a peracetic acid-based disinfectant to Atlantic salmon parr reared in recirculating aquaculture systems

There is a high regard for peracetic acid (PAA)-based disinfectants in recirculating aquaculture systems (RAS) because of the low risk of bioaccumulation, fast degradation with neutral residuals and minimal impact on biofilter performance. However, the no-observed-effect concentration in Atlantic salmon parr is unknown. The present study evaluated the effect of an acute PAA exposure on Atlantic salmon parr health and welfare by evaluating survival, swimming behaviour, appetite and histopathological alterations in the gills and skin. Nine experimental RAS units were employed, where each unit was dedicated for one PAA concentration (0.0, 0.05, 0.1, 0.2, 0.4, 0.8, 1.6, 3.2 and 6.4 mg/L). Fish were exposed to the target PAA concentration in a static system for 1 h and the exposure protocol was repeated after a 52 h recovery. The fish survival was 100%, 80% and 0%, respectively ≤1.6, 3.2 and 6.4 mg/L. Fish swimming behaviour was normal in PAA ≤ 1.6 mg/L, whereas it become erratic with air gasping for PAA ≥ 3.2 mg/L. The fish appetite did not change among the different PAA treatment groups. Skin and gill histopathological alterations were pronounced in PAA ≥ 3.2 mg/L, characterized by a poorer skin condition and necrotic gill lamella. The skin acidic mucous cells density was 55% lower in the 6.4 mg/L group than the 0 mg/L group. The sub-lethal water pH values observed in the 6.4 mg/L group after PAA administration may have played a confounding and compounding factor to the PAA toxicity response in this group. In conclusion, the current study identified the no-observed-effect concentration for PAA to be below 1.6 mg/L for Atlantic salmon parr and provided insights into its use as a water prophylactic strategy in RAS. Toxicity of PAA-based disinfectants is influenced by its acidified nature, which can interfere with the water pH of low alkalinity aquaculture systems. Further studies should evaluate the health and welfare consequences of a long-term PAA exposure in Atlantic salmon parr