Largemouth Bass Fact Sheet

Prepared by Scott Syska, Tommie Crawford, and Stephanie Ramsey-Westbrook, Missouri Department of Conservation

What is Largemouth Bass Virus?

Largemouth bass virus (LMBV) is a fish disease that first gained recognition in 1995 during a July-September fish kill of 1,000 adult largemouth bass at Santee-Cooper Reservoir in South Carolina. During the summer of 1999 LMBV was first detected in Missouri during a fish kill of several hundred largemouth bass at Table Rock Lake. To date LMBV has been confirmed in bass populations in Table Rock Lake, Lake of the Ozarks, Wappapello Lake, Lake Springfield, Harry S. Truman Reservoir, Bull Shoals Lake, and Norfork Lake in Missouri. LMBV has been found in obviously sick fish and normal healthy fish. Not all sick fish in an infected lake are sick from LMBV. Even though LMBV has been detected in Missouri waters we have not documented a case where LMBV was diagnosed as directly causing a fish kill.

The origin of the disease in unknown but it is in a family of viruses known as Iridoviruses which affect cold-blooded animals. LMBV is almost identical to a virus found in some aquarium fish. It is unknown if LMBV is naturally occurring or if it was accidentally introduced by people transporting fish, water, or fish parts from infected areas. Although the virus can be carried by other species of fish, so far it has only created disease in big largemouth bass.

Signs of Infected Fish

Most fish with LMBV are carriers with no disease signs whatsoever. Although other diseases and parasites can cause sores on fish, Largemouth bass that are sick with LMBV have difficulty swimming, but otherwise still appear normal without visible sores. Sick fish may look bloated and struggle at the surface before dying. LMBV mainly appears to affect the swim bladder causing affected fish to have difficulty swimming normally. A yellowish cheese-like substance has been reported inside the swimbladder of some infected fish. Disease outbreaks have mainly been reported during the warm summer months and appear to only involve big largemouth bass. It seems that warm water temperatures, improper angler handling of fish, low oxygen, and other stresses may predispose fish to develop the disease, since healthy unstressed fish do not tend to develop the disease.

Are Infected Fish Safe to Eat?

Yes. LMBV is not known to affect humans or and other mammals or birds. LMBV does not change the flesh of the fish. However, if fish have other diseases or open sores they may not be good to eat.

What is MDC Doing About the Virus?

There is no cure or treatment for infected fish. Most fish, including most big largemouth bass, appear unaffected by the virus. However, the Missouri Department of Conservation (MDC), the US Fish and Wildlife Service (USFWS), and many other state agencies throughout the country are working to learn more about LMBV. MDC continues to provide funding and samples to support LMBV research at Auburn University. MDC is continuing to participate in the National Wild Fish Health Survey where MDC personnel and USFWS personnel work cooperatively to test wild fish populations in waters across Missouri for a variety of diseases and parasites.

What Effects Will LMBV Have on Fishing?

The effects of LMBV appear to be short term, with bass populations recovering after even a large kill in two to three years. When LMBV does cause a kill usually only a small percentage of the population is lost. MDC is currently investigating the condition of bass in infected lakes to check for nonlethal effects in lakes which have not experienced a kill but where there has been a slump in aggressive strikes by fish. Overall, no long term bass fishing affects are anticipated based on the experiences other states have had with the virus. MDC will continue to strive to provide the best angling possible for Missouri anglers.

What Can You Do?

Anglers can help prevent the spread and the impact of LMBV by:

1. Do not move fish, fish parts, or water from one body of water to another.
2. Clean with hot water and thoroughly dry boats and equipment before using at different bodies of water. (Always drain the water from your boat at the same place you got the water in your boat.)
3. Handle fish as gently as possible if you will be releasing them. Be especially careful during warm weather. Methods to do this include: avoid damaging the fishÕs protective slime layer, keep the fish in water as much as possible, do not stick your fingers into the gills of the fish, release the fish as quickly as possible, and if fish must be held before releasing: make certain your live-well is well aerated with cool water and that water does not drain out when the boat accelerates while boating from place to place.
4. Tournaments should be held during cooler weather at infected lakes, and overcrowding live-wells should be avoided
5. If you see dead or dying fish or evidence of pollution call your local Missouri Department of Conservation Office or Conservation Agent.