Diseases and parasites in salmon

Infected fish presented with multiple skin lesions which were almost inevitably suffering overgrows of Saprolegnia fungus.

[2] However, as opposed to whirling disease, the Henneguya infestation does not appear to cause significant incapacitation of the host salmon — even heavily infected fish tend to return to spawn successfully.

Work on Henneguya salminicola at the Pacific Biological Station in Nanaimo[3] noted that "the fish that have the longest freshwater residence time as juveniles have the most noticeable infections.

As well, the report says that, at the time the studies were conducted, stocks from the middle and upper reaches of large river systems in British Columbia such as Fraser, Skeena, Nass and from mainland coastal streams in the southern half of B.C.

According to Klaus Schallie, Molluscan Shellfish Program Specialist with the Canadian Food Inspection Agency, "Henneguya salminicola is found in southern B.C.

I have previously examined smoked chum salmon sides that were riddled with cysts and some sockeye runs in Barkley Sound (southern B.C., west coast of Vancouver Island) are noted for their high incidence of infestation."

In the Pacific, Sea lice, particularly Lepeophtheirus salmonis and various Caligus species, including C. clemensi and C. rogercresseyi, can cause deadly infestations of both farm-grown and wild salmon.

[12] Enteric redmouth disease is a bacterial infection of freshwater and marine fish caused by the pathogen Yersinia ruckeri.

[13] The bacteria Piscirickettsia salmonis causes the disease piscirickettsiosis, which has a mortality rate as high as 90% in certain salmonid fishes and is ubiquitous on Chilean salmon farms.

Amongst other measures, this requires the total eradication of the entire fish stock should an outbreak of the disease be confirmed on any farm.

The disease can progress slowly throughout an infected farm and, in the worst cases, death rates may approach 100 percent.

It was first discovered in 2010, present in Atlantic Salmon farms exhibiting high levels of Heart and Skeletal Muscular Inflammation (HSMI) and Cardiomyopathy syndrome (CMS).

[22] In the wild, diseases and parasites are normally at low levels, and kept in check by natural predation on weakened individuals.

[26][27] These predictions have been disputed by other scientists[28] and there is much debate on whether the correlation between sea lice infestation and declining wild salmon stocks is driven by causal factors.