MORAVIA - The presence of largemouth bass virus (LMBV) was confirmed in Lake Sugema by the U.S. Fish and Wildlife Service La Cross Fish Health Lab in La Cross Wis. Mark Flammang, fisheries management biologist with the Iowa Department of Natural Resources stationed at Lake Rathbun, investigated a report of dead and dying fish on Aug. 3.
"We were seeing only dead largemouth bass. No dead walleyes or other species which is unusual if the kill was caused solely by low oxygen conditions, so we had to look for something else," Flammang said. He said many of the dead largemouth bass were longer than 15 inches and the numbers were in the hundreds. Flammang submitted fish for analysis on Aug. 9 and received the confirmation on Aug. 15.
Largemouth bass virus was first detected at the Santee-Cooper Reservoir in South Carolina in 1995 and has been an issue for states in the south. It has since been found in at least 23 other states, including Iowa in 2002, when it was confirmed in Pools 10 and 11 of the Mississippi River.
Flammang said LMBV is a short-term issue for a lake and once the virus is present it becomes part of the ecosystem and a tool for natural selection. 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," Flammang said. "None of these fish have obvious signs that they have the virus. Some largemouth bass that carry the virus may have red sores, but this is caused by secondary infections and is not directly related to the virus."
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. This includes humans."
As is the case with most viruses, Flammang 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 Flammang said a number of conditions at Lake Sugema caused a lot of stress to the fish population, and that stress can make fish more vulnerable to virus.
Sugema had a massive growth of curly leaf pond weed, which is a fairly common exotic species in many Iowa lakes that dies off naturally when the water temperature reaches 70 degrees. This decaying vegetation directly removes oxygen from the water and provides a large pulse of nutrients that can lead to an algae bloom.
Calm and cloudy days caused the algae to die off which removed more oxygen from the water. Those two factors combined with the warm lake water temperature caused an oxygen sag for a few days. The oxygen sag causes stress in the fish population, especially largemouth bass, and hit larger fish the hardest. That stress is the opening the LMBV needs to impact the fish.
Flammang said anglers can help prevent the spread of LMBV by handling largemouth bass gently if they are going to release them and by not moving fish from one body of water to another. Anglers are reminded that it is illegal to stock or introduce any live fish into public waters without the permission of the director of the DNR. 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.
"It was pretty disheartening as an angler and as a biologist," he said. "We had the bass population moving in the direction we wanted it." Lake Sugema has a special regulation protecting largemouth bass between 12 and 18 inches in length. Anglers can harvest largemouth bass below 12 inches and above 18 inches. He said bass fishing at the lake may be impacted immediately after the outbreak, but will bounce back and anglers are still encouraged to harvest bass less than 12 inches for consumption.
"There is really nothing we can do about it once it enters a lake," he said. "It is now part of the system, but the impacts will level out. Over time, Mother Nature finds a way."
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