Annual report on health monitoring of wild anadromous salmonids in Norway 2023 - Screening of Atlantic salmon postsmolts from Boknafjorden and Hardangerfjorden and sea trout from Hitra for pathogen infections

Abstract

The Institute of Marine Research has investigated the prevalence of infectious salmon anemia virus (ISAV), salmonid alphavirus (SAV, PD virus), piscine orthoreovirus 1 (PRV-1), piscine myocarditis virus (PMCV) and bacterial kidney disease (BKD) infections in wild postsmolt Atlantic salmon and sea trout caught in 2023 in three aquaculture production areas (PO2, 3 and 6). The fish were collected as part of the national monitoring program for salmon lice. The postsmolts were taken in outer parts of Boknafjord (N = 50) and Hardangerfjord (N = 50) by trawling in the period May-June. The sea trout was caught using gillnet and fish trap in Hitra area in June. Low concentrations of SAV-RNA were detected in two post smolts from the Boknafjord and one post smolt from the Hardangerfjord. ISAV was detected in one fish from Boknafjorden, one post smolt from Hardangerfjorden and one sea trout from Hitra. PRV1 was detected in 6 post smolts, 5 from Boknafjorden and one from Hardangerfjorden. Low concentrations of PMCV were detected in 9 fish. The PMCV-positive postsmolts were collected from both fjords. There was also one PMCV-positive sea trout from Hitra. Virus-positive fish had high Ct-values ​​(34-40) and these values represent probably weak or false positive results. Renibacterium salmoninarum (causative agent of BKD) was not detected in any postsmolt or sea trout. The results in the current report showed that postsmolt and sea trout from fjords had a very low occurance of pathogen infections, which is common in Norwegian aquaculture. These findings complement and confirm our previously reported data and may indicate that the prevalence of pathogen infections in wild salmon post-smolt and sea trout is not significantly affected by the occurrence of these infections in fish farming.

Annual report on health monitoring of wild anadromous salmonids in Norway 2023 - Screening of Atlantic salmon postsmolts from Boknafjorden and Hardangerfjorden and sea trout from Hitra for pathogen infections