Abstract

In 1997, the National Wild Fish Health Survey (NWFHS) was initiated under the leadership of US Fish and Wildlife Service Regional Fish Health Centers in cooperation with stakeholders such as Tribes, states, and the aquaculture industry. The survey was a response to the association of Whirling Disease with a precipitous decline in wild trout populations in the intermountain west. This decline focused the nation's attention on the fact that very little is known about diseases among wild fish. The purpose of the survey is to determine the distribution of certain pathogens in wild fish. The data collected is available to the public at the website, http://wildfishsurvey.fws.gov/.

During the last eight years, the NWFHS has dramatically increased our knowledge of the geographical range of known pathogens, expanded the number of species these pathogens have been documented in, and have resulted in the detection of previously unknown viruses. In addition, the data has been used to determine suitability of broodstock for recovery programs of listed species. In cooperation with the states and other federal agencies, the NWFHS has played an important role in surveillance of exotic diseases such as Spring Viremia of Carp Virus. In addition, findings from the NWFHS have laid the groundwork for research including development of non-lethal sampling techniques and species susceptibility studies. The data collected, along with associated research, provide natural resource managers with additional information to make sound, scientifically based decisions.

Hatcheries are under intense scrutiny due to possible interactions between hatchery and wild fish.¹ Several publications discussing the theoretical impacts on wild fish from a fish health perspective can be found in the literature.^2,3 As part of the NWFHS, studies are being conducted by the Olympia Fish Health Center and the Lower Columbia Fish Health Center on the Entiat River, Icicle Creek, Eagle Creek, Wind River, Warm Springs River, and Shitike Creek in Washington State and Oregon. These water bodies have anadromous fish hatcheries and barriers upstream of the hatchery that prevent fish passage. The sites above the barriers are considered to be areas free of hatchery influence. Although these surveys alone are not likely to fully address the fish health interaction question, they provide valuable data that may help focus future efforts.

In the first two years of a three year survey at the Entiat River and Icicle Creek, 737 fish were sampled for bacterial culture, 674 for viral testing, 777 for Enzyme Linked Immunosorbent Assay (ELISA) testing for Renibacterium salmoninarum (the causative agent of Bacterial Kidney Disease), and 851 for Myxobolus cererbralis (the causative agent of Whirling Disease).

None of these pathogens other than R. salmoninarum were detected. ELISA profiles of Oncorhynchus mykiss (rainbow trout/steelhead trout) differed above and below the barriers. Due to many confounding factors such as collection methods, habitat differences, potential influence of non-hatchery anadromous fish, and limitations of the assay, the significance of this finding is unknown. However, the data collected from these studies, and the NWFHS in general, provide crucial baseline on the presence and range of pathogens in wild fish populations.

References

1.  Brannon E, Amend D, Cronin MA, S LaPatra. 2004. The Controversy About Salmon Hatcheries, Fisheries, Vol 29, No. 9, Pp. 12-31.

2.  Hasted T, T Linstad. 1991. Diseases in Wild and Cultured Salmon: Possible Interaction. Aquaculture, Vol. 98, Pp. 277-288.

3.  Noakes DJ, Beamish R J, ML Kent. 2000. On the Decline of Pacific Salmon and Speculative Links to Salmon Farming in British Columbia. Aquaculture, Vol. 183, Pp. 363-386.