About 220 fish died at Lake of the Pines in Nevada County in September, and state wildlife officials have now linked largemouth bass virus to the die-off, with tests confirming its presence in California for the first time. The dead fish were mostly largemouth bass, with some bluegill mixed in, and officials still don't know how the pathogen got into the lake in the first place.
The California Department of Fish and Wildlife confirmed the virus's presence through necropsies, according to The Sacramento Bee, which reported that the dead fish included largemouth bass and bluegill. The agency said it had not determined how the virus reached the water, leaving the source of the outbreak unresolved even as the investigation continues. California Department of Fish and Wildlife confirmed the presence of the virus in the state for the first time in its own announcement.
State Checking Other Lakes for Spread
Wildlife officials are now investigating whether the virus has turned up anywhere else in California, and they're asking anglers and lake visitors to report any significant die-offs of largemouth bass they come across, the Bee's report notes. The agency has emphasized that the virus poses no health risk to people or other warm-blooded animals, but it is a serious concern for fish populations.
According to the same account, the virus can be introduced to a body of water through contaminated equipment, infected baitfish, the stocking of infected largemouth bass, or the introduction of other infected carrier species. Fish such as spotted bass, bluegill and crappie can carry and transmit the virus without ever showing symptoms themselves, which makes tracking its spread especially tricky.
No Cure, and a Virus That's Hard to Shake
Once largemouth bass virus takes hold in a population, it is extremely difficult to eradicate, per the state agency's findings. There are no treatments or vaccines available, and outbreaks can drag on for days or weeks before fading on their own, the report states.
To slow further spread, officials are urging people to avoid moving fish between different bodies of water and to clean, drain and dry boats and fishing equipment after every outing. Infected fish can show symptoms like bulging eyes, erratic swimming, darkened skin and skin sores, and the disease typically affects adult fish, which may lose their equilibrium and end up floating at the surface, according to a fisheries review published in the journal Fisheries. That review also notes that fish kills have struck some infected bass populations hard, while in other locations the virus lingers in bass and other species without causing any visible illness at all.
A Virus With a Murky Past, Now Spreading Nationwide
Largemouth bass virus isn't new to the country, even if it's new to California. Accounts of exactly when and where it first appeared don't fully agree. The Sacramento Bee reports it was first documented in Florida in the 1990s before spreading throughout the United States, while the Fisheries review places its first isolation in Florida in 1991, and the Texas Parks and Wildlife Department says it was first found in Florida in the 1980s, with the first fish kill tied to the virus occurring at South Carolina's Santee-Cooper Reservoir in 1995 before it later turned up in states including Indiana, Michigan, Illinois and Vermont, according to the Texas Parks and Wildlife Department.
Whatever its exact origin, the virus has clearly become a nationwide presence. The Washington Animal Disease Diagnostic Laboratory at Washington State University notes that largemouth bass virus has been detected throughout the United States in recent years. Federal researchers have documented its reach before, too: the U.S. Fish and Wildlife Service's LaCrosse Fish Health Center identified the virus during annual sampling in Pools 3 and 7 of the Upper Mississippi River, and the agency said it was working with partners to determine just how widespread the infection had become.
A fish die-off at Lake of the Pines has been linked to the virus, and state investigators are checking other lakes. The source remains unidentified, and anglers across the region are being asked to do their part by keeping gear clean and fish where they're caught.
