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Largemouth Bass Virus in New Hampshire


What is Largemouth Bass Virus?

Largemouth bass virus (LMBV), one of more than 100 naturally occurring viruses in fish. Fish with largemouth bass virus are safe to handle and eat, as the virus does not infect warm-blooded animals, including humans.


Has LMBV been detected in New Hampshire?

In 2007, smallmouth bass collected during the summer from Lake Winnipesaukee by the New Hampshire Fish and Game Department tested positive for LMBV. "It is probable that the virus exists in other water bodies in the state, however, based on the information we have to date, it is unlikely that largemouth bass virus poses a serious threat to the long-term health of New Hampshire's bass resources," said Gabe Gries, NH Fish and Game fisheries biologist and the Department's Warmwater Project Leader.


The previous year (2006), largemouth and smallmouth bass collected during the summer by the New Hampshire Fish and Game Department had tested negative. Bass examined that year included 10 from the Connecticut River, 16 from Winnisquam Lake and 58 from Lake Winnipesaukee.


To date, where has LMBV been found?

Largemouth bass virus was first detected in Florida in 1991 and gained national attention in 1995, when it was found to be the cause of a largemouth bass kill in South Carolina. The virus was originally thought to be restricted to the southern U.S., but it has since been detected in some Northeastern states. These include Vermont (Lake Champlain), Connecticut, and New Hampshire (where it was detected in 2007 in Lake Winnipesaukee).


What role can anglers play in limiting the spread of LMBV?

Because the virus can sometimes kill or otherwise negatively impact largemouth bass and can be spread or influenced by anglers, it is critical that anglers become educated about how they can help prevent the spread of this virus.


Impact on the fishery

Presence of the virus in a fish population does not necessarily mean fish will develop LMBV disease, which can cause them to die or show signs of being in poor health. The virus appears to result in disease when largemouth bass are stressed; warm water temperatures, low oxygen, poor water quality and frequent handling can increase the chance that fish may exhibit the disease. Although the virus can be carried by other fish species, such as smallmouth bass, chain pickerel, redbreast sunfish, black crappie and bluegill, it is only known to be fatal to largemouth bass. The ability of other species, such as baitfish, to carry the virus is unknown.


Most fish carrying largemouth bass virus appear completely normal, but largemouth bass kills sometimes result in waters that test positive for LMBV. These fish kills generally occur during the summer months, indicating that warmer water temperatures may be a factor. In cases where the virus has triggered disease, dying bass may be near the water surface and have difficultly swimming and remaining upright. The virus attacks the swim bladder, sometimes causing bass to lose their equilibrium and appear bloated. Largemouth bass between 12 and 15 inches appear to be most susceptible to the disease. The occurrence of lesions or black spots is not necessarily a sign that a fish has LMBV.


No evidence currently exists that the virus has caused long-term impacts to a fishery; some data indicate that an infected fishery will recover over a period of years.


How is LMBV transmitted, and what waterbodies have been tested?

Scientists are unsure as to how the virus is transmitted or how it is activated into disease. There is currently no cure or preventative for LMBV, and it can live in water for up to seven days. The virus may be transmitted through water, by fish consuming infected prey, or through direct and indirect contact in boat live wells.


The NH Fish and Game Department has tested waterbodies with high inter-state boat traffic, including Lake Winnipesaukee (2006 and 2007), Lake Winnisquam (2006) and the Connecticut River (2006). Testing occurred during the summer, when the virus/disease is known to be most active. NH Fish and Game worked with bass clubs holding tournaments on these waterbodies to collect fish samples.


Anglers can help minimize the impact and spread of largemouth bass virus by following these suggested guidelines:


  • Drain water from bilge and live wells and clean boats, trailer and other equipment between fishing trips with a solution of bleach to water (1:100 ratio) and let air-dry.
  • Never transfer fish or fish parts from one body of water to another. In fact, NH law prohibits transfer of live fish from one water to another.
  • Do not release live bait into waterbodies.
  • Handle bass as gently as possible.
  • During times of high water temperatures, minimize stress to fish as much as possible.
  • Conduct fishing tournaments during cooler weather, so fish caught will not be as stressed.
  • Reduce daily bass tournament bag limits or use a "paper format" during times of high water temperatures.
  • Report dead or dying fish to the NH Fish and Game Department.
  • Educate other anglers about LMBV.


For more information on warmwater fisheries management in NH, contact:


New Hampshire Fish and Game Department, Region 4, 15 Ash Brook Court, Keene, NH 03431; phone (603) 352-9669