Two California Department of Fish and Wildlife (CDFW) fish hatchery facilities in the eastern Sierra have recently detected an outbreak of Lactococcus petauri, a naturally occurring bacteria that sickens fish. CDFW fishery managers are working to implement strategies that will help the facilities get the disease under control, without cancelling all trout plants prior to the traditional season opener on April 30.

The affected facilities – Black Rock Hatchery and Fish Springs Hatchery – usually provide fish for stocking waterways in CDFW’s Inland Deserts Region. Both facilities experienced a similar outbreak of Lactococcus garvieae in 2020, which led to the euthanization of approximately 3.2 million fish in order to stop the spread of disease (L. petauri is molecularly very similar to L. garvieae; the general abbreviation for both strains is Lactococcus spp.).

Earlier this month, the four raceways that hold catchable fish at Black Rock Hatchery tested positive for the Lactococcus bacteria. This accounts for approximately 120,000 trout, which would normally be stocked throughout the fishing season. At Fish Springs Hatchery, all lots of catchable fish (approximately 550,000 trout) tested positive. The current outbreak is among fish that have already received one round of vaccination.

In lieu of depopulating the affected hatcheries, non-diseased fish will be stocked into high-use waters that are hydrologically connected to the affected hatcheries and have cold water. This will mean increased plants for some locations and decreased plants for others. Diseased fish will be euthanized and not planted.

“This is unfortunate timing, as it affects our planting efforts in the weeks before the opener, but all is not lost,” said CDFW Director Charlton H. Bonham. “Fortunately, we learned much from the 2020 outbreak, and we have more knowledge and better tools to fight the bacterium this time around. We also believe we can continue stocking, with some adjustments and careful monitoring.”

Prior to the 2020 outbreak of Lactococcus, which is similar to streptococcus, the bacterium had never before been detected in fish in California, and thus there were no known effective treatments to employ. CDFW put three facilities under quarantine for more than a month(opens in new tab), while pathologists and hatchery staff treated the affected fish. CDFW was successful in developing vaccines and continue to work on vaccine-related issues to improve efficiency.

Lactococcus spp. occurs naturally in the environment and is usually spread by movement of fish or eggs. CDFW’s fish pathologists believe that it may have been carried into the hatcheries by birds that picked it up from an environmental source. The current strain of bacteria is identical to one found in fish farms in central Mexico, which lends support to the hypothesis that birds using the pacific flyway are the likely vector for the spread of the bacteria. Fish that are infected with the bacterium 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. As always, anglers should follow USDA recommendations on cooking fish to an internal temperature of 145 degrees F.

CDFW has initiated a phased priority stocking plan for the eastern Sierra. This plan will focus on planting high-use waters in southern Mono and northern Inyo counties. Similar to measures taken to handle the 2020 outbreak, CDFW will be investigating all available options to secure additional fish for increased planting opportunities, including redirecting fish plants from non-infected hatcheries. Results of the latest testing at Hot Creek Hatchery indicate that the fish in that facility’s upper raceways are cleared for planting at this time.

For additional information, please see CDFW’s frequently asked questions about the Lactococcus spp. outbreaks (PDF)(opens in new tab).