Susquehanna Smallmouth Sickness Solved

Mystery solved: Susquehanna River smallmouth bass are back

A college laboratory is credited with solving a maddening mystery: What killed so many smallmouth bass in the lower Susquehanna and Juniata rivers, beginning in 2005?

The answer, which came as a surprise to some Pennsylvania and federal investigators, is largemouth bass virus.

At the time, several environmental problems were impacting the river, in particular a mystery disease that left sores and open wounds on young smallmouths. Scientists couldn’t agree on its source for more than a decade. But now the disease has virtually disappeared.

“Like it never happened, but it did,” said Darrell Franks, a Greensburg fisherman whose family has fished near their camp in York County since the 1960s. “A lot of guys still won’t fish the Susquehanna because of the disease, but that’s their mistake. The fishing is better than ever.”

The disease that impacted the smallmouths is common among largemouths and cannot infect humans. When well cooked, afflicted fish are safe to eat despite the ick factor. Investigators knew early on that the disease was present in Susquehanna smallmouths but it had been ruled out as the cause of the lesions. Scientists believed it couldn't hurt them.

It turned out that largemouth bass virus can be lethal to smallmouths when shallow water near river banks, where young bass generally live, becomes stagnant and warm. In that environment, the virus does not kill but causes lesions and sores where bacteria and fungus enter the fish’s body, eventually killing them.

Science, conservation and politics didn’t eliminate the disease. As some researchers had always expected, nature healed itself. Mr. Franks said there have never been so many big bass in his neck of the river.

 It happens more often than you think.

The mystery was solved by scientists at Michigan State University who injected smallmouth bass from a Pennsylvania fish farm with the virus. Their experiments proved that mortality increased when the fish were in summerlike warm water.

Either the current generation of Susquehanna smallmouths have built an immunity to the virus or it has mutated in a way that no longer impacts bronzebacks. A catch-and-release regulation on 98 miles of the river, and nearly 32 miles of the Juniata River, seem to have given the fish the space they needed to survive. Fishing for smallmouths has rebounded since 2017. Some anglers say it is as good today as in the early 1990s.

It should be pointed out that Largemouth Bass are not native to the Susquehanna drainage, having been introduced as a game fish, presumably bringing their diseases with them.

The Wombat has Rule 5 Sunday: Homeko At The Beach up at The Other McCain.