The Mysterious Catfish Tumors of South River

'We definitely have to do more research as to why'

A new study found the culprit is not a group of toxins called PAHs that often cause tumors in fish. The cause may be a virus or other contaminant, according to the lead researcher, Fred Pinkney of the U.S. Fish and Wildlife Service's Chesapeake Bay Field Office in Annapolis.

"If you read detective stories, I imagine we're trying to sift through the evidence," Pinkney said. "Sometimes they give it up easily, sometimes you have to work on them."

The tumor-ridden brown bullhead catfish were first documented in the South River in 2004 after they were found during a separate survey involving other fish. More than half of the fish collected then had unsightly tumors growing around their mouths and 20 percent had liver tumors.

Hmm.  That's news to me.  That last I'd heard, PAHs were the prime suspect in this local problem.  So where else have they found the tumors?

Fish also were collected in the Severn, Rhode and Choptank rivers for analysis. The Severn had a wide range of fish with skin tumors (2 percent to 52 percent). A few Rhode River catfish had skin tumors (6 percent) and almost no skin tumors were found in Choptank catfish.

Scientists performed a variety of tests on the fish, including looking at their DNA, to determine the cause of the tumors. They did not find a correlation between the tumors and the presence of polynuclear aromatic hydrocarbons, chemicals found in gas, oil, coal, car exhaust and runoff from highways. They also didn't find a link between the tumors and another group of chemicals called alkylating agents.

It's not clear from the article whether they examined exposure to PAHs as well as concentrations of PAH in the catfish themselves.  PAHs are pretty rapidly metabolized by vertebrates, and it's the intermediates of their metabolism which do most of the damage.  I'm sure the USFW people understand that, but it certainly didn't come out clearly in the article.

There's a big slug of trace metals in the South River too, but they're mostly natural.