Largemouth Bass Virus Found in Arizona Waters

USFWS/La Crosse Fish Health CenterArizona may have a new microscopic aquatic invader - largemouth bass virus, which can kill fish but is not harmful to people.


"There has been a preliminary detection of this fish virus at Saguaro Lake," said Arizona Game and Fish Department Fisheries Chief Kirk Young.

Fish samples from Saguaro recently showed preliminary results for the largemouth bass virus, but due to testing timelines for this disease, Arizona Game and Fish is still awaiting a full report from federal laboratories. The full report is expected in the next three to four weeks. Confirmation of the detection will then be sought with another, independent laboratory.

Young emphasized that even if the virus is present, the disease posses no risk to people and pets and the water is safe for drinking water supply and recreation. "Largemouth bass virus is not known to infect any warm-blooded animals and any fish that are caught by anglers are safe to eat," said Young. "However, we always recommend that you thoroughly cook any fish you intend to eat and never use found dead or dying fish for food."

If confirmed, Saguaro would be the first water in Arizona to test positive for the presence of the virus. Although not previously detected in Arizona, at least 18 other states have found the fish disease in bodies of water dating back to 1991.


Game and Fish is working to develop a sampling effort to determine the presence of this fish virus in other Arizona bass lakes.

Largemouth bass virus can cause fish mortality but does not always do so. "It is not precisely known what triggers the activation of the virus into a disease outbreak, but it has been associated with stress events such as high water temperatures," Young said. "The virus only affects largemouth bass, but other fish species can carry the virus as well as water itself."

In other locations around the country where the virus has been found, bass populations typically suffer one-time effects of the disease before infected waters returned to normal. The virus appears to diminish over time and not every infected fish becomes sick. For instance, only five lakes in Texas suffered fish kills even though the virus was found in 23 of the state's reservoirs. "Usually the number of infected fish that die is relatively low compared to the entire population, with the virus mostly affecting older and larger fish," said Young.


Young emphasized that even though testing results are only preliminary at this point, Game and Fish wanted to inform the public immediately rather than waiting for full confirmation. "If the virus is present, there are precautions the public can take to help stop the spread of the virus," Young said. "As with all aquatic invasive species such as quagga mussels, public awareness and cooperation are critically important to preventing an even larger problem."

One preventive measure that's vital is that people absolutely avoid transporting live fish or water from one body of water to another.

"You might be spreading an unwanted disease or even introducing an unwanted organism that could prove deadly to a fishery or substantially alter a lake ecosystem," said Young. "Don't transport live fish caught from a lake - period. It's the wrong thing to do and it's unlawful."

It's also important to clean, dry and drain your boat before leaving any lake at any time, and to disinfect your boat or wait at least five days before launching your boat on another water. In fact, at several lakes it's now the law that you do so. This is extremely important as the bass virus can live for up to seven days in standing water.

Other ways anglers and boaters can help stop the spread of invasive species:

  • Dispose of all unused bait in the trash, never in the water.
  • Never transfer live fish from one body of water to another.
  • Rinse any mud and/or debris from equipment and wading gear.
  • Drain any water from boats, bilge, bait buckets, and live wells before leaving the launch area. A mild mixture of bleach and water can be used to disinfect your equipment. Allow everything to air dry before moving to another body of water.
  • Stage fishing tournaments in cooler weather to reduce stress on caught bass.
  • Run aerators continuously while fish are in live wells if temperatures are over 70 degrees.
  • If you see any dead or dying fish, please report your observation to Game and Fish.
  • Educate others to follow these steps.
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