Our Bay: Scientists research bacteria afflicting rockfish

By PAMELA WOOD, Staff Writer
The Capital, Published 07/17/10

Pamela Wood — The Capital Mark Matsche of the Maryland Department of Natural Resources cuts a rockfish open as he demonstrates a necropsy, or animal autopsy, at the Cooperative Oxford Lab on the Eastern Shore.

OXFORD - It was more than a dozen years ago when Chesapeake Bay rockfish started turning up skinny and pockmarked with nasty skin lesions, and scientists are still figuring out what's going on.

Scientists soon determined the culprit was mycobacteriosis, a bacterial disease.

But understanding how the bacteria works - how it spreads, how it sickens the fish, how it affects the overall fish population - is a mystery that's still being unraveled.

"When people started getting these, that's what triggered everyone's attention," said Mark Matsche, a Maryland Department of Natural Resources biologist, pointing to a photo of a sick fish at the Cooperative Oxford Laboratory on the Eastern Shore.

Scientists in Maryland and Virginia quickly got to work researching mycobacteriosis.

Since then, public attention to myco and rockfish has waxed and waned, often spurred by media reports.

The most recent flare-up was in 2006, fueled in part by an article in The Washington Post about the disease.

In the wake of the article, other media (including The Capital) jumped on the story. Wholesale prices for rockfish dropped and scores of charter fishing trips were canceled.

In an attempt to quell the situation, then-Gov. Robert L. Ehrlich Jr. ate rockfish and mashed potatoes in the Governor's Mansion kitchen, which was packed full of reporters and cameramen.

Over time, public and media attention eventually shifted elsewhere. Crabs and oysters took the spotlight.

But scientists are as focused as ever on myco.

Fish, human health problems

The myco problem in rockfish is unique in its persistence from year to year, Matsche said. Often fish diseases come and go, lasting for a season or maybe a year, he said.

"This is sort of a big mystery," he said.

When fish get infected, the most outwardly visible sign is ugly, red lesions on the skin.

But the main mode of attack for the bacteria is to target the spleen.

As the bacteria damages the spleen, the fish responds by covering up spleen ulcers with new tissue that forms into nodules like little gray BBs.

As a result, a fish's spleen can bloat up from a typical 3 inches to an unhealthy 10 inches.

The severity of the infection can vary greatly, and the majority of infections are mild or moderate, Matsche said.

"Just like any disease, you get a range," he said.

Mycobacteriosis has caused human problems, too. Some anglers have contracted the bacteria from infected rockfish, resulting in serious hand and arm infections.

Called "fish handler's disease," myco infections can get so bad that they require hospitalizations, surgeries and serious medications.

There were 25 reported cases of human myco infections in Anne Arundel County in 2008, according to Elin Jones, a county Health Department spokeswoman.

That's up from 13 cases in 2007, five cases in 2006 and 11 cases in 2005.

Data from 2009 isn't yet available.

Recreational and commercial fishermen and charter boat captains and crew are advised to be careful when handling rockfish. Wearing gloves is a good idea, as is washing or using hand sanitizer after handling live rockfish.

Cooked rockfish is not believed to be harmful to humans.

Research questions

It's not clear why myco - commonly found in the water - continues to make bay rockfish sick.

One popular theory, especially among anglers, is that rockfish are overwhelmed by persistent pollution and a lack of food to eat, including the small, oily menhaden fish.

It's not known yet how myco is transmitted. Maybe it floats in the water, maybe it moves from fish to fish. Scientists don't know the answer yet.

The infection rates rise as a fish grows older, although for an unknown reason, infection rates drop off for females age six and older.

Myco infections grew more common in rockfish from 1998 to 2004, when it began leveling off, Matsche said.

Currently, 40 to 70 percent of rockfish have myco infections, he said.

Myco is fatal to fish, as researchers from the Virginia Institute of Marine Science reported in the scientific journal Ecological Applications in 2008.

The VIMS team determined an infected fish is only 70 percent as likely to live another year as a noninfected fish.

To reach their findings, scientists in Virginia and Maryland have been getting intimately acquainted with a whole bunch of dead fish.

Matsche's team examines fish at a rate of 600 per year, sampling different ages, sizes and locations.

They give each fish a thorough post-mortem examination called a "necropsy." (Necropsy is the term for an autopsy done on animal.)

To start, the physical examination during the necropsy can give clues, such as the skin sores or enlarged spleen. But that's not foolproof - up to 30 percent of fish that physically appear healthy are, in fact, infected.

Scientists also take cultures and grow any bacteria in a lab and see what type is there - there are actually 13 different mycobacteriosis species.

They also can use a technique called "PCR," a way to amplify DNA, to look for myco in tissue samples.

Scientists also get information through a fish-tagging program.

They go out and catch fish, examine them and affix special tags before releasing them back into the water. When an angler later catches the fish, they call a phone number on the tag and report information about the fish.

Researchers hope that eventually, all those fish will reveal more clues to solve the myco mystery.

"We're getting the fish back and we're getting good information," Matsche said.

(Revised July 2010)