Some Potential Fish Health Concerns for Threatened and Endangered Species and Other Fishes in the Upper Colorado

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CDOW -BRUSH TEL No.303- 842 -2849 Apr 10,92 14:09 No.003 P.02 SOME POTENTIAL FISH HEALTH CONCERNS FOR THREATENED AND ENDANGERED SPECIES AND OTHER FISHES IN THE UPPER COLORADO RIVER BASIN OF COLORADO Peter G. Walker, Fish Pathologist Colorado Division of Wildlife State Fish Health Laboratory P.O. Box 128 Brush, Colorado 80723 VIRUSES No viruses have as yet been isolated from any of the Colorado River T &E sucker and minnow species. No viruses have been isolated from any fish species, cultured or wild, within the Colorado River Basin of the state of Colorado for at least eight years. one potential virus that might represent a threat to T &E minnows and /or suckers is the causative virus of Spring Viremia of Carp (SVC) in Europe. Fish introductions into the Basin from any outside source should be carefully considered with regard to potential pathogens. BACTERIA I know of no reports of serious bacterial outbreaks in any Basin T &E minnows and suckers. However, many obligate bacterial fish pathogens and virtually all opportunistic fish pathogens re- present potential risks of some degree, although it nearly always takes stressful human- caused or environmental conditions as predis- posing factors in any bacterial outbreak. Two obligate bacterial fish pathogens, Yersinia ruckeri, causative agent of Enteric Redmouth (ERM) , and Aeromonas salmonictda, causative agent of Furunculosis, are known to be established in fish popula- tions in the Basin. Y. rucked is probably widespread in salmonid populations. While ERM has been reported from nonsalmonid popula- tions including an. outbreak in emerald shiners (Notropis atherinoides) in Wyoming (Doug Mitchum, pers. Comm.), it is considered by most fish health workers to be primarily a disease of trout and salmon. Y. rucked has been established and widespread throughout Colorado for at least two decades. Salmonid fish culturists employ antibiotics and commercial bacterias ( "vaccines ") to keep the organism under control where needed. The disease and pathogen are not regulated in Colorado. A salmonictda has caused epizootics in both cultured and feral fishes several times in the past five years in the Upper Colorado River Basin. Epizootics in feral fish were recorded in the Eagle River between Edwards and Wolcott and in the East River above Al- mont. In addition, the cause of a late summer brown trout die -off in the Frying Pan River was unconfirmed but highly suspect. Salm- onid species, particularly feral brown trout, were involved in virtually every case. To date only one nonsalmonid species, the -j