Largemouth Bass Virus Linked to Susquehanna Smallmouth Bass Disease

A little Largemouth Bass

Scientists scrutinize virus, contaminants in smallmouth bass die-off

For more than a decade, biologists have been picking away at a mystery: What caused a years-long decline of smallmouth bass in Pennsylvania’s Susquehanna River starting more than a decade ago?

Some think they may have finally cracked the case. The results of recently published research, lauded by some as “the smoking gun,” points to a virus once thought not to affect smallmouth bass. In a series of laboratory experiments, scientists from Michigan State University found that largemouth bass virus can indeed be fatal to young smallmouth bass.

Others are not ready to stamp “case closed” on the mysterious die-off, saying the full explanation is much more complicated.

A bigger Largemouth Bass

Biologist Vicki Blazer of the U.S. Geological Survey Leetown Science Center is one of them. Blazer has been leading a long-term study of wild bass from the Susquehanna. Her team of federal and state researchers has been working on the premise that multiple infections of disease and parasites caused the widespread deaths of young smallmouth bass that was first observed in 2005.

Those infections, she argues, may have been triggered by a brew of chemicals polluting the Susquehanna that weakened fish immune systems.

“The bottom line was, from site to site, there was no one pathogen that we were finding,” Blazer said. “Most of the places that had mortality had multiple pathogens. That led us to think that something was going on to be immunosuppressing those fish and making them more susceptible to disease.”

Brooke Thomas displays a beer and a Smallmouth Bass

When fish get ill, they often fall prey to numerous secondary infections. You have to be very careful to actually get to the bottom of the reason for the illness. Vicky Blazer has a hammer, and she's looking for a convenient nail.

That’s not to say that largemouth virus isn’t the cause of the fish kills.

“The research has shown that the largemouth bass virus is capable of killing smallmouth bass at water temperatures that continue to exist in the Susquehanna,” said Coja Yamashita, a fisheries biologist with the Pennsylvania Fish and Boat Commission who worked with the Michigan lab during the study. “The virus is one piece of the puzzle, just a much larger part than we originally thought.”

Yamashita said that while there’s no way to remove the virus from the river, educating anglers and boaters is needed to help stop its spread. The virus was most likely transported by boats and equipment from other waters into the Susquehanna.

“As far as what Vicki Blazer is doing, there’s no doubt that contaminants in the water aren’t helping the situation,” he said. “Identifying which toxins are the worst for fish health — that’s something we can do something about.”

The Susquehanna is sick, and only a serious cleanup is going to fix it.

Wombat-socho was a day late with "Rule 5 Sunday: Crystal Hefner".