Alternative prophylaxis/disinfection in aquaculture - Adaptable stress induced by peracetic acid at low concentration and its application strategy in RAS

Abstract

The application of peracetic acid (PAA) at low concentrations has been proven to be a broad-functioning and eco-friendly prophylaxis/disinfection method against various fish pathogens. However, there is lack of knowledge on how to apply PAA in a recirculating aquaculture system (RAS), and whether the application of PAA at low concentration can affect fish welfare. In the present study, PAA was applied in a pilot-scale carp (Cyprinus carpio) RAS (comprised of a fish culture tank of 1m3, a reservoir tank of 600L and a filter complex of 400L) every 3 or 4days for 5weeks, and the stress response of fish was monitored during every second PAA application by measuring cortisol in water. Results showed that the increase of water cortisol became less pronounced and the decrease of water cortisol occurred earlier after repeated applications of PAA, which indicates an adaptation of the stress response to PAA in the carp. Moreover, the mathematic model showed that the equal distribution of PAA in RAS was a slow progress, which depended on tanks size and flow rate. To avoid potential harm to the biofilter in RAS during PAA application, it's suggested that PAA should be applied only to the fish culture tank at a reduced flow rate. Statement of relevanceFish welfare becomes more and more important in aquaculture. However, there is a lack of knowledge if routine prophylaxis/disinfectant might affect fish welfare. In the present study, we tested how fish responded to repeated applications of peracetic acid (PAA) in a pilot-scale recirculating aquaculture system (RAS) via measurement of cortisol in water. The results showed that fishes reduced their stress during subsequent PAA application, indicating adaptation of fish to repeated prophylaxis/disinfection with PAA. Moreover, we established a model and measured the PAA concentration onsite to investigate the distribution of PAA in RAS. We found out that by simply adding PAA only to the fish culture tank with a reduced flow rate can avoid the potential harm on the biofilter. Findings from the current study provide insights that may prove of benefit to future treatment based studies.