Carbaryl, Carbofuran, and Methomyl - National Marine Fisheries ...

Whirling disease is a parasitic infection caused by the microscopic parasite Myxobolus
cerebrali. Infected fish continually swim in circular motions and eventually expire from
exhaustion. The disease occurs in the wild and in hatcheries and results in losses to fry
and fingerling salmonids, especially rainbow trout. The disease is transmitted by infected
fish and fish parts and birds.
IHN is a viral disease in many wild and farmed salmonid stocks in the Pacific Northwest.
This disease affects rainbow/steelhead trout, cutthroat trout (Salmo clarki), brown trout
(Salmo trutta), Atlantic salmon (Salmo salar), and Pacific salmon including Chinook,
sockeye, chum, and coho. The virus is triggered by low water temperatures and is shed
in the feces, urine, sexual fluids, and external mucus of salmonids. Transmission is
mainly from fish to fish, primarily by direct contact and through the water.
Sea lice also cause deadly infestations of wild and farm-grown salmon. Henneguya
salminicola, a protozoan parasite, is commonly found in the flesh of salmonids. The fish
responds by walling off the parasitic infection into a number of cysts that contain milky
fluid. This fluid is an accumulation of a large number of parasites. Fish with the longest
freshwater residence time as juveniles have the most noticeable infection. The order of
prevalence for infection is coho followed by sockeye, Chinook, chum, and pink salmon.
Additionally, ich (a protozoan) and Columnaris (a bacterium) are two common fish
diseases that were implicated in the massive kill of adult salmon in the Lower Klamath
River in September 2002 (CDFG 2003; Guillen 2003).
Predation
Salmonids are exposed to high rates of natural predation, during freshwater rearing and
migration stages, as well as during ocean migration. Salmon along the U.S. west coast
are prey for marine mammals, birds, sharks, and other fishes. Concentrations of juvenile
salmon in the coastal zone experience high rates of predation. In the Pacific Northwest,
the increasing size of tern, seal, and sea lion populations may have reduced the survival
of some salmon ESUs.
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