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Lactococcus garvieae outbreak forces euthanization of fish at Southern California hatcheries

Wednesday, July 29, 2020

As reported July 9, (Bacterial outbreak in U.S. trout hatcheries halts fish stocking in Southern California), three California Department of Fish and Wildlife (CDFW) fish hatchery facilities in the eastern Sierra and Southern California, USA, have been battling a bacterial outbreak that has affected 3.2 million fish. This week, after consultation with fish pathology experts and exhausting all avenues of treatment, CDFW announced that the fish, which are all trout, at the affected facilities must be euthanized in order to stop the spread of the outbreak. The affected facilities – Mojave River Hatchery, Black Rock Hatchery and Fish Springs Hatchery – usually provide fish for stocking waterways in CDFW’s South Coast Region and Inland Deserts Region. The euthanization of all the fish at these facilities will have a profound effect on CDFW’s ability to stock fish for anglers in those regions in the near future.

“Euthanizing our hatchery stocks was not a decision we came to lightly, but it had to be done,” said Jay Rowan, environmental program manager for CDFW hatcheries. “This bacterium is resistant to all the treatment options we have available for fish. The fish losses were getting worse despite our treatments. The best option we have available that will get us back to planting fish from these hatcheries in the shortest timeline is to clear the raceways, thoroughly disinfect the facilities, and start over.”

CDFW has had the three facilities under quarantine for more than a month, while pathologists and hatchery staff treated the affected fish and researched potential options. The outbreak of Lactococcus garvieae, which is similar to Streptococcus, has been reported in cattle and poultry farms as well as fresh and saltwater fish and shellfish hatcheries around the world, but had never before been detected in fish in California. Research of treatment options employed at trout farms in Europe and other parts of the world show there has almost no chance for successfully eliminating the bacteria from a facility without depopulation and disinfection.

Fish that are infected with Lactococcus garvieae can show symptoms including bulging eyes, lethargic or erratic swimming and increased mortality, or be asymptomatic and show no signs of infection depending on several factors including water temperature and stress. Fish-to-human transmission of this bacteria is rare and unlikely but there are several documented instances associated with immunocompromised people consuming infected raw fish and unpasteurized milk products.

Hot Creek Hatchery in the eastern Sierra has tested negative for the bacteria and is still planting eight waters in Inyo and Mono counties. CDFW is in the process of developing a modified stocking plan to reallocate fish from central and northern California hatcheries to a small number of high angler use, easily accessible waters in geographically distinct parts of the eastern Sierra and Southern California.

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