Paulo Mira Fernandes

Persistence of Infectious Salmon Anaemia Virus (ISAV) and the effect of practical biosecurity interventions was evaluated in small-scale moving-bed RAS units and bioreactors. ISAV HPRΔ infected Atlantic salmon (~ 50 g) were stocked to three RAS units containing 15 ppt brackish water and removed after 14 days. After removal of shedder fish, the systems were drained, lightly scrubbed, refilled and fallowed for a variable period before restocking with naïve fish. In parallel, biomedia from each RAS unit were transferred to triplicate bioreactors and exposed to three field-relevant biosecurity treatments i.e. no treatment, water replacement, or ozonation. In the RAS units, detectable ISAV RNA levels increased in water, swab, and biomedia samples during the shedding period, peaking on the day when shedder fish were removed (day 0). Thereafter, detection declined rapidly, with water and swab samples consistently indicating higher ISAV RNA levels than biomedia (p = 0.004). The virus could not be detected 17 days post-removal of shedder fish. All naïve fish were ISAV-negative at the end of study. ISAV RNA detection levels varied according to treatment and sample matrix, with no detection in the ozonated reactors and sporadic detection in the bioreactors with the two other treatments up to 14 days after onset of the biosecurity intervention. The findings indicate that ISAV may persist transiently in the RAS environment with uncertain infectivity post fallowing and may be influenced by several factors such as environmental conditions, host-pathogen interactions and support the use of ozone as an effective disinfection method of water and biomedia.

Persistence of Infectious Salmon Anaemia Virus (ISAV) and the effect of practical biosecurity interventions was evaluated in small-scale moving-bed RAS units and bioreactors. ISAV HPRΔ infected Atlantic salmon (~ 50 g) were stocked to three RAS units containing 15 ppt brackish water and removed after 14 days. After removal of shedder fish, the systems were drained, lightly scrubbed, refilled and fallowed for a variable period before restocking with naïve fish. In parallel, biomedia from each RAS unit were transferred to triplicate bioreactors and exposed to three field-relevant biosecurity treatments i.e. no treatment, water replacement, or ozonation. In the RAS units, detectable ISAV RNA levels increased in water, swab, and biomedia samples during the shedding period, peaking on the day when shedder fish were removed (day 0). Thereafter, detection declined rapidly, with water and swab samples consistently indicating higher ISAV RNA levels than biomedia (p = 0.004). The virus could not be detected 17 days post-removal of shedder fish. All naïve fish were ISAV-negative at the end of study. ISAV RNA detection levels varied according to treatment and sample matrix, with no detection in the ozonated reactors and sporadic detection in the bioreactors with the two other treatments up to 14 days after onset of the biosecurity intervention. The findings indicate that ISAV may persist transiently in the RAS environment with uncertain infectivity post fallowing and may be influenced by several factors such as environmental conditions, host-pathogen interactions and support the use of ozone as an effective disinfection method of water and biomedia.