Marine reservoirs of infectious agents associated with proliferative gill disorders in farmed salmon
Gill diseases and disorders among Atlantic salmon raised in seawater net pens are an emergent and important cause of losses. There is a need to better describe the causes, distribution, and possible control of gill diseases, which can be caused by algal blooms, jellyfish, parasites, bacteria, viruses, and other non-infectious agents.
This project focused on proliferative gill disorders and parasites, such as Paramoeba perurans and Desmozoon lepeophtherii, to improve understanding of reservoirs of infections (where the infectious agent normally lives, grows, and multiplies). Infectious and non-infectious causal factors were studied in populations of wild and farmed fish sharing common bodies of water to better understand the epidemiology of proliferative gill disorders.
The project goal was to develop knowledge related to the distribution and causes of gill disorders in British Columbia (BC) to inform further development of farmed fish health management strategies and improve the understanding of the role of gill disorders in the conservation of wild salmon.
There was a high prevalence of pathological lesions in the gills of Atlantic salmon reared by three companies in all regions studied. Despite an association between level of D. lepeophtherii and clinical disease, there was no consistent relationship between the presence/absence of D. lepeophtherii, sea lice (Lepeophtheirus salmonis) or P. perurans and the presence of pathological lesions.
The magnitude of disease and infection in farmed salmon depended both on the location of the farm and on the time of sampling. Although very few wild salmon had microscopic evidence of gill disease, there was a relatively high rate of D. lepeopherii infections. The severity of D. lepeophtherii was occasionally increased in samples displaying acute clinical gill disease. A previously undescribed virus was detected in gill samples from two farms.
The project concluded that the extent of gill disease in farmed salmon in BC varies by farm and over time and parasite infections occur frequently in gills from farmed and wild salmon.
2016 - 2018
Gary Marty, Senior Diagnostic Fish Pathologist, BC Ministry of Agriculture’s Veterinary Diagnostic Laboratory, Animal Health Centre
Sonja Saksida, Veterinary Epidemiologist, Fisheries and Oceans Canada, Pacific Region
Marc Trudel, Research Scientist, Fisheries and Oceans Canada, Pacific Biological Station, Pacific Region
Diane Morrison, Director of Fish Health and Food Safety, Marine Harvest Canada Limited
Sharon DeDominicis, Regulatory Compliance and Certification Director, Marine Harvest Canada Limited
Jeremy Dunn, Executive Director, BC Salmon Farmers Association
Joanne Liutkus, Project Manager, BC Salmon Farmers Association
Mairi Edgar, Project Manager, BC Salmon Farmers Association
Tim Hewison, Fish Health and R&D Manager, Grieg Seafood Ltd.
Danielle New, Cermaq Canada
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