3/20/2007

Largemouth Bass Virus Found at Brown's Lake in Pool 13 of the Upper Mississippi River

BELLEVUE - The presence of Largemouth Bass Virus (LMBV) was confirmed in Brown's Lake in Pool 13 of the Upper Mississippi River by the U.S. Fish and Wildlife Service La Crosse Fish Health Lab, in La Crosse, Wis. Mike Steuck, fisheries research biologist with the Iowa Department of Natural Resources (DNR) stationed at Bellevue, collected the largemouth bass samples in late October 2006.

"We were seeing a good number of skinny largemouth bass. We did not find any largemouth bass dead or see other species in poor conditions. When we returned a week later to collect the fish for analysis, we found very few fish in poor condition," Steuck said. The DNR collected largemouth bass of all sizes to be analyzed for the LMBV. Steuck said that although poor body condition is not an associated symptom of LMBV, it did make them take a closer look and see if the virus was there.

Brown's Lake is a backwater in Pool 13 of the Mississippi River about 10 miles south of Bellevue. The DNR collects largemouth bass samples annually from Brown's Lake to evaluate the catch and release regulation on black bass. "Information collected during the sampling allows us to evaluate the regulation and also to keep track of the condition of these fish," Steuck said. "We've looked at the largemouth bass length and weight data from the past 20 years and found no change in the condition of those fish. We have a very healthy population of largemouth bass."

Largemouth bass virus was first detected at the Santee-Cooper Reservoir in South Carolina in 1995 and had been an issue for states in the south. It has since been found in 23 other states, including Illinois, Minnesota, Missouri and Wisconsin, LMBV has been detected in Iowa in 2002, when it was confirmed in Pools 10 and 11 of the Mississippi River and in 2005 at Lake Sugema.

Steuck said LMBV is a short-term issue for a lake and once the virus is present, largemouth bass will build up their immune system to address it. Subsequent outbreaks impact fewer fish than the initial one.

"The virus is in the water and only affects largemouth bass. However, other fish species can be carriers," Steuck said. "Affected largemouth bass do not have obvious signs that they have the virus. We just happened to sample the fish before the fish were stressed and the virus had a chance to flourish." In some populations affected by LMBV sores and lesions can be found on the fish.

As for the question "are the fish safe to eat," he said anglers should use their best judgement. "Cook the fish thoroughly," he said. "The fish are safe to consume, but you probably should avoid eating sick or dying fish or animals of any species. The virus is not transferable to warm-blooded animals."

As is the case with most viruses, Steuck said there is not a lot that can be done once LMBV is present in a lake. How the virus arrived is difficult to say, but he said a number of conditions could occur at Brown's Lake or other backwater lakes on the Mississippi River to stress the fish population, and that stress can make fish more vulnerable to the virus.

Stress can lower the fish's natural defenses against disease and can be the opening the LMBV needs to impact the fish. Bass living in the Mississippi River may encounter a variety of stressful conditions including poor water quality consisting of low water levels, high temperatures and low dissolved oxygen levels; repeated handling by anglers, long distance movements to the few over wintering areas and crowded conditions in suitable backwater habitats.

Steuck said anglers can help prevent the spread of LMBV by handling fish gently if they are going to release them and by not moving fish from one body of water to another. Anglers should also follow the rules by not releasing live bait into the water and to call the DNR if they see dead or dying fish. Anglers can also thoroughly disinfect their live wells and holding tanks with a bleach mixture made of 1 cup of bleach in 1 gallon of water and let it soak for 30 minutes. This bleach concentration and soak time is sufficient to kill the virus.

This is especially important with the finding of Viral Hemorrhagic Septicemia (VHS) which has been found to cause large fish kills in the Great Lakes Region. VHS is another pathogen that has been found to infect at least 37 fish species including bass, walleye, bluegill, crappie, channel catfish, northern pike and musky. "We want to minimize the spread of any disease in our aquatic systems just as we wouldn't want to spread the flu from person to person where we live, work or go to school," Steuck said.

For more information, contact Steuck at 563-872-5495.