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Fish Diseases in Coastal Mendocino Streams

KRIS Web Background Pages: Fish Disease

(The following information is from personal communication with Dr. Bill Cox, California Department of Fish and Game (CDFG) Pathology Lab, Sacramento, CA. Although the surveys described are not currently published, they may be by Dr. Cox in the future).

Noyo River coho salmon have been transplanted widely throughout northern California. Fish from Oregon rivers were also mixed with the native broodstock at the Noyo Egg Collecting Station in the 1970s (see Hatchery section). Stock transfers pose a risk of disease introduction. There is no baseline data about endemic fish diseases in Mendocino streams.

CDFG conducted surveys of many Mendocino coastal streams, including the Noyo River, to determine if fish diseases were constraining production of coho salmon. The specific disease that was suspected was bacterial kidney disease (BKD). Samples were limited because the number of coho salmon found in some streams was very small and no coho were captured in others. No significant levels of disease were found in the coho salmon or steelhead sampled. The likelihood of transmission of BKD between planted fish and wild fish is low because of low fish densities in the stream environment. Horizontal transmission between introduced coho and native steelhead is also unlikely because of the higher inherent resistance of steelhead to BKD.

The concern of BKD was raised because Noyo River eggs incubated at the Warm Springs Hatchery on the Russian River consistently gave rise to juvenile fish that tested positive for BKD. The same eggs incubated at Mad River Hatchery hatched into fish with no signs of the disease. Transfers of Noyo River coho eggs to warm Springs Hatchery were consequently discontinued.