The invasive northern snakehead fish found in the mid-Atlantic area is now cause for more concern, potentially bringing diseases into the region that may spread to native fish and wildlife, according to a team of U.S. Geological Survey scientists.

The team found that a group of adult northern snakehead collected from Virginia waters of the Potomac River south of Washington D.C. were infected with a species of Mycobacterium, a type of bacteria known to cause chronic disease among a wide range of animals.

"Mycobacterial infections are not unusual among fish, but they are nonetheless noteworthy because they can have an impact at the population level and potentially even affect other fish and wildlife," said lead author Christine Densmore, a veterinarian with the USGS.

There are many known species of Mycobacteria that have been identified in fish, including fish from the Potomac River and Chesapeake Bay area.  Several years ago, mycobacterial infections were associated with severe disease typified by ulcerative skin lesions and wasting among wild striped bass from the Chesapeake Bay and its tributaries.  Some species ofMycobacterium are also known to cause diseases among other animals, including mammals. For instance, Mycobacterium tuberculosis is the cause of human tuberculosis andMycobacterium paratuberculosis, causes Johne’s disease of cattle. 

The effect of this particular species of Mycobacterium on humans is not known.

Mycobacterial disease in fish is often called piscine mycobacteriosis, and it is associated with many different species of mycobacteria. In this instance, no external signs of disease were noted on the infected snakehead fish, and the disease was discovered microscopically as lesions associated with the bacteria that were visible within internal organs.

"Another interesting feature of this particular mycobacterial organism is that we have not been able to identify it in the available gene sequence data base, so this may be a unique, undescribed species of Mycobacterium. However, more research is needed to further characterize the bacteria and its potential effects on the northern snakehead population and other native species," said Densmore.

The researchers plan to continue to work closely with other federal and state agencies to investigate the pathogens and diseases carried by the northern snakehead fish in mid-Atlantic waters such as the Potomac River.  This study of Mycobacterial infection in Northern snakehead from the Potomac River catchment, conducted in collaboration with fisheries biologists from the Virginia Department of Game and Inland Fisheries, is available onlinethrough the Journal of Fish Diseases.