Piscine orthoreovirus (PRV) in red and melanised foci in white muscle of Atlantic salmon (Salmo salar).
Melanised focal changes (black spots) are common findings in the white skeletal muscle of seawater-farmed Atlantic salmon (Salmo salar). Fillets with melanised focal changes are considered as lower quality and cause large economic losses. It has been suggested that red focal changes (red spots) precede the melanised focal changes. In the present work, we examined different populations of captive and wild salmon for the occurrence of both types of changes, which were investigated for the presence of different viruses by immunohistochemistry and RT-qPCR. The occurrence of red or melanised foci varied significantly between the populations, from none in wild fish control group, low prevalence of small foci in fish kept in in-house tanks, to high prevalence of large foci in farm-raised salmon. Large amounts of Piscine orthoreovirus (PRV) antigen were detected in all foci. No other viruses were detected. Red focal changes contained significantly higher levels of PRV RNA than apparently non-affected areas in white muscle of the same individuals. Some changes displayed a transient form between a red and melanised pathotype, indicating a progression from an acute to a chronic manifestation. We conclude that PRV is associated with the focal pathological changes in the white muscle of farmed Atlantic salmon and is a premise for the development of focal melanised changes.
Institute of Basic Science and Aquatic Medicine, School of Veterinary Medicine, Norwegian University of Life Sciences, Oslo, Norway. havard.bjorgen@nmbu.no.
Håvard
H
Bjørgen
Institute of Food Safety and Infection Biology, School of Veterinary Medicine, Norwegian University of Life Sciences, Oslo, Norway. oystein.wessel@nmbu.no.
Øystein
Ø
Wessel
Matre Research Station, Institute of Marine Research, Matre, Norway. pergf@IMR.no.
Per Gunnar
PG
Fjelldal
Matre Research Station, Institute of Marine Research, Matre, Norway. tomh@IMR.no.
Tom
T
Hansen
Lerøy Seafood Group ASA, Bergen, Norway. harald.sveier@leroy.no.
Harald
H
Sveier
Department Brandasund and Rex Star, Lerøy Sjøtroll AS, Skjervøy, Norway. hakon.rydland.sabo@leroy.no.
Håkon Rydland
HR
Sæbø
Lerøy Aurora AS, Skjervøy, Norway. katrine@leroyaurora.no.
Katrine Bones
KB
Enger
Lerøy Aurora AS, Tromsø, Norway. eirik@leroyaurora.no.
Eirik
E
Monsen
Institute of Basic Science and Aquatic Medicine, School of Veterinary Medicine, Norwegian University of Life Sciences, Oslo, Norway. agnar.kvellestad@nmbu.no.
Agnar
A
Kvellestad
Institute of Food Safety and Infection Biology, School of Veterinary Medicine, Norwegian University of Life Sciences, Oslo, Norway. espen.rimstad@nmbu.no.
Espen
E
Rimstad
Institute of Basic Science and Aquatic Medicine, School of Veterinary Medicine, Norwegian University of Life Sciences, Oslo, Norway. erling.o.koppang@nmbu.no.
Erling Olaf
EO
Koppang
D000818:Animals; D017756:Aquaculture; D005393:Fish Diseases / Q000453:epidemiology* / Q000821:virology; D018482:Muscle, Skeletal / Q000821:virology; D009664:Norway / Q000453:epidemiology; D018165:Orthoreovirus / Q000302:isolation & purification*; D015995:Prevalence; D012088:Reoviridae Infections / Q000453:epidemiology / Q000662:veterinary* / Q000821:virology; D020317:Salmo salar