The California Department of Fish and Wildlife (CDFW) has confirmed the presence of Largemouth Bass Virus (LMBV) for the first time in California.
The highly pathogenic virus was found in largemouth bass and bluegill in Lake of the Pines, a private, 232-acre lake in Nevada County, following a fish die-off in September that claimed approximately 220 fish, mostly largemouth bass but some bluegill as well.
Necropsies performed at CDFW’s Fish Health Lab confirmed the viral infection. The source of the infection has not been identified. LMBV can be introduced from contaminated equipment, infected baitfish, stocking infected largemouth bass and introducing other carrier species that are infected.
LMBV does not pose any risk to humans or other warm-blooded animals. There are no health concerns to anglers who consume largemouth bass or recreational users who swim in or drink LMBV infected water. CDFW recommends that fish are properly prepared to prevent other food-borne illnesses.
“This is a sobering discovery given how widely distributed largemouth bass are in California, how popular they are as a sport fish and their economic importance to our rural communities,” said Jay Rowan, CDFW Fisheries Branch Chief. “We’re asking all Californians to help prevent any further spread by not moving fish, alive or dead, from one waterbody to another and by cleaning, draining and drying their boats and fishing equipment after use.”
LMBV was first documented in Florida in the 1990s but has since spread throughout the United States. It is extremely difficult to eradicate from a largemouth bass population once infected. The virus is specific to largemouth bass but can also cause disease in other fish species such as smallmouth bass. Other species, such as spotted bass, bluegill and crappie, can carry and transmit the virus without showing symptoms of the disease.
LMBV outbreaks can last days or weeks before they resolve on their own. There are no available treatments or vaccines to prevent an outbreak. Typically, an outbreak will result in the mortality of a high percentage of the larger size classes of largemouth bass in the infected waterbody. Surviving fish eventually build resistance to the virus over time and populations can recover. However, there can be significant impacts to populations of larger fish for years after an initial outbreak.
Infected largemouth bass can exhibit a wide range of disease signs such as skin sores or ulcers, darkened skin, distended body cavity, bulging eyes, redness, lethargy, erratic swimming behavior, surface swimming and difficulty submerging. Stressful events and environmental conditions such as elevated water temperatures in the summer, poor water quality and angling pressure can activate the disease in infected fish.
Anglers and recreational users of any body of water should assume LMBV is present and take the following precautions:
- Do not move any fish, alive or dead, or any part of the fish, from the body of water unless for immediate consumption. If cleaning fish, do so at the waterbody where they were caught or at home. Place all fish parts into the trash.
- Place leftover bait into the trash.
- Any watercraft or boat used should be drained of any water before leaving the area. This includes water in bait tanks, bilges, livewells, wash down lines, etc.
- Handle fish you intend to release with care. Stress seems to increase fatalities of fish infected with LMBV.
- Any fishing or recreational or recreational equipment that comes in contact with water or mud after use should be rinsed, cleaned or dried before leaving the area.
- Wash gear in hot water and allow it to dry thoroughly before using at a different waterbody.
CDFW is working to determine if LMBV is present in any other waterbodies in California. Please report any significant largemouth bass mortality events to your nearest CDFW regional office.
For more information on LMBV, please see the following FAQs.