Bacterial outbreak forces California to cull 3.2 million trout

Approximately 3.2 million hatchery trout will be euthanized this month in California due to a rare bacterial outbreak, according to a California Department of Fish and Wildlife (CDFW) press release.

An outbreak of Lactococcus garvieae affected fish in three hatcheries: Mojave River Hatchery, Black Rock Hatchery, and Fish Springs Hatchery. These three facilities provide fish that stock waterways in California’s South Coast and Inland Deserts Regions.

The bacteria is similar to streptococcus and has been seen in fish and shellfish hatcheries as well as in cattle and chicken farms, but it is the first reported outbreak in California.

Although the possibility of transmission to humans is rare, there have been documented cases of people with immune disorders becoming infected after eating contaminated raw fish or unpasteurized milk products.

Fish infected with the bacteria can display bulging eyes, erratic or lethargic swimming, or can show no symptoms – depending on stress and water temperature. Increased mortality in fish populations is also associated with the bacteria.

“Euthanizing our hatchery stocks was not a decision we came to lightly, but it had to be done,” said CDFW Environmental Program Manager Jay Rowan. “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.”

The CDFW said that research from trout farms in other areas of the world has shown that it’s virtually impossible to eliminate the bacteria from the farm without total depopulation and disinfection.

As a result of the outbreak, the CDFW is reallocating fish from other hatcheries in the northern and central regions of the state to plant in areas frequented by anglers. 

Photo courtesy of the California Dpeartment of Fish and Wildlife