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striped bass infected with mycobacteria

Characteristic lesions caused by mycobacteriosis, a disease that's affecting a large proportion of striped bass in the Chesapeake Bay. (photo courtesy of Maryland Department of Natural Resources)

NOAA Studies Shed New Light on Bacterial Disease Affecting Chesapeake Bay Striped Bass Population

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Mycobacteriosis (shown here in a fish spleen under magnification; bacteria are red) causes a serious and often lethal infection in a wide range of species around the world. There are currently no widely accepted cures.

These bacteria have received increasing attention in recent years because of the discovery of new species of the bacteria in fish hosts, sharp increases in incidence rates in wild fisheries, and the ability of a few species of the bacteria to infect humans.

If you’re an angler in the Chesapeake Bay region, you may be familiar with the term ‘myco.’ It’s slang for mycobacteriosis, a serious disease that affects up to 70 percent of adult striped bass in the Bay.

For years, scientists have been racing to understand more about the harmful bacteria that cause this disease and potential implications for the management of the fishery.

This year, we learned much more about the problem thanks to new research conducted by NOAA and partners. Two studies published in 2009 provide important new clues into how widely this disease is distributed, as well as how long it has been around in the Bay region.

In a study published in the Journal of Aquatic Animal Health in October, researchers found two types of mycobacteria common in striped bass in Bay-area white perch. The study also found mycobacteriosis in stripers located outside of the Chesapeake Bay region.

While scientists are not surprised to find mycobacteria in striped bass from other areas, it's not clear if this indicates that the bacteria are moving to new areas or if the findings are a result of increased surveillance. Likewise, study authors note that it's 'not entirely surprising' to find that the same strains of mycobacteria infecting striped bass are also infecting white perch, since this fish is a close relative and shares similar habitats and habits. Nonetheless, the report marks an important step forward in what is known about the disease. In addition, the findings point to the need for more investigation into other potential host species and geographic areas where mycobacteriosis may be found.

In a second study published in Diseases of Aquatic Organisms in July, researchers found evidence of mycobacteriosis infection in striped bass dating back to 1984 by examining archived bass tissue samples. Previously, the earliest known cases of the disease stemmed from 1997.

This finding establishes a more accurate timeline of the presence of the disease in the region. It also underscores the importance of keeping archived samples of animal tissue in storage for use in studying the causes, distribution, and timeline for a given disease.

Together, the two studies may help scientists get closer to answering basic questions about the distribution and potential sources of mycobacteria in the region.These answers are needed to maintain the health and vitality of one of the most important commercial and recreational fisheries in the Mid-Atlantic region.

*The Cooperative Oxford Lab, administered by NOS, is a shared research facility between NOAA, Maryland's Department of Natural Resources, and the U.S. Coast Guard.