The California Department of Fish and Wildlife (CDFW) has detected a bacterial outbreak at its Hot Creek Trout Hatchery in Mono County – the second time in 2021 that Lactococcus garvieae has been confirmed in some trout at the hatchery.

Three distinct groups of trout representing about 15 percent of the hatchery’s total trout population have tested positive. CDFW has quarantined the facility, temporarily suspended fish planting and is preparing to humanely euthanize infected fish and vaccinate uninfected stocks.

“The encouraging news is that we caught the outbreak early as part of our routine testing and only a portion of the hatchery’s trout has been infected,” said Jay Rowan, CDFW’s statewide hatchery program manager. “We now have proven and effective vaccines to protect uninfected fish – vaccines developed recently in a partnership between UC Davis and CDFW. We’re in the process of vaccinating the hatchery’s healthy fish populations. Unfortunately, we don’t have a cure or treatment for infected fish at this time.”

Hot Creek Trout Hatchery is located south of Mammoth Lakes and raises three species of trout – rainbow, brown and Lahontan cutthroat – for stocking into some blue-ribbon eastern Sierra fisheries, including Crowley Lake, Pleasant Valley Reservoir and portions of the Owens River. CDFW expects low to moderate impacts to waters stocked by the Hot Creek Trout Hatchery in 2022.

The 15 percent of infected fish consist of 118,000 rainbow trout and 52,000 brown trout, including 2,000 broodstock brown trout weighing 2 to 3 pounds each.

Nearly a million fish have tested negative and will undergo vaccination, either through a bath immersion process for smaller, juvenile fish or injection into larger fish. These healthy populations include rainbow trout broodstock, brown trout broodstock, rainbow and brown trout of various sizes, and juvenile Lahontan cutthroat trout. Once vaccinated, the fish will be safe to plant and safe for anglers to consume.

Lactococcus garvieae is the same disease that forced the quarantine and suspension of fish planting last year at three other CDFW trout hatcheries in Southern California and the eastern Sierra – the Mojave River Hatchery, Black Rock Trout Hatchery and Fish Springs Trout Hatchery. That outbreak ultimately forced the euthanization of 3.2 million trout at those hatcheries.

All three hatcheries have undergone intensive cleaning, disinfection and are raising fish once again. Fish Springs and Black Rock are back stocking trout for recreational fishing. Those two hatcheries have vaccinated all of their fish stocks, which continue to test negative for the disease.

Isolation of Lactococcus garvieae in a few fish at the Hot Creek Trout Hatchery earlier this year resulted in the temporary quarantine of the facility and the suspension of fish stocking. Other CDFW trout hatcheries outside of the eastern Sierra have assisted stocking waters in Inyo and Mono counties while the Hot Creek Trout Hatchery has been offline and while Fish Springs and Black Rock were rebuilding their fish populations.

The outbreak of Lactococcus garvieae, which is similar to streptococcus or strep throat, has been reported in cattle and poultry farms as well as fresh and saltwater fish and shellfish hatcheries around the world. It had never before been detected in fish in California until the hatchery outbreaks in 2020.

Fish that are infected with Lactococcus garvieae can show symptoms that include 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 the bacteria is rare and unlikely but there are several documented instances associated with immunocompromised people consuming infected raw fish and unpasteurized milk products.