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New eel parasite could pose a serious threat in Atlantic Canada

A team of biologists from Cape Breton University and Saint Mary’s University have discovered a harmful new eel parasite in Cape Breton.

CBU marine ecologist Dr. Martha Jones says her team has made the first documented report in Canada of the invasive nematode worm Anguillicoloides crassus. The worm infects American eels (Anguilla rostrata) and may pose a serious threat to the region’s eel population, which is already under consideration for the Canadian federal Species at Risk Act (SARA).

A. crassus lives in the eel’s swimbladder, where it can cause the thickening or rupture of the lining, weakening the host. It is also thought to prevent infected fish from migrating to their spawning grounds, and may contribute to increased mortality. It has been linked to the collapse of the European eel population, and is considered a major threat to European eel fisheries. There has also been a marked decline in eel populations throughout North America, and A. crassus is another addition to an already long list of possible causes including habitat degradation, climate change, and pollution.

The parasite was found by graduate student Lydia Rockwell during collaborative research led by Dr. Jones into fish and their parasites in Cape Breton estuaries. The young adult (yellow-stage) American eels were gathered in the summer of 2007 from the Mira River and Sydney Harbour. Rockwell and her supervisors, Dr. Jones and Dr. David Cone of Saint Mary’s University, found that six of ten eels gathered from Mira River, and one of five from Sydney Harbour were infected by A. crassus, with an intensity of between 1 to 11 worms per eel.

To confirm the find, the team sent specimens to the Czech parasitologist František Moravec, a leading authority on the spread of A. crassus around the world. A. crassus originates in Asia, where it infects the Japanese eel (Anguilla japonica) without causing them serious harm—but the European eel (Anguilla anguilla) and the American eel are less resistant to its effects. International trade in eels led to the accidental introduction of the parasite into Europe in the 1980s; the first documented case in North America was in 1995, at a southern-Texas aquaculture facility. It is thought to have been sent infected elvers by a supplier.

Quite how A. crassus arrived in Cape Breton is not yet understood, but one prolific way for exotic aquatic species to move around the globe is in the ballast water of ships. As vessels are loaded and unloaded with fuel and cargo, ballast water must be pumped in or out to maintain stability. Between 3,000 and upwards of 10,000 species may be transported around the world in the ballasts of ships daily. Dr. Jones says that if ballast water did introduce A. crassus into Cape Breton, it is more likely to have been through shipping activity in the Strait of Canso or the Bras d’Or Lakes, rather than Sydney Harbour—where most vessels arrive fully loaded, hence without ballast water. 

Once introduced into freshwater and estuarine environments, A. crassus spreads rapidly among eel populations—a 100-percent infection rate within a year is not unknown. We do not yet know which other species A. crassus uses in North America to complete its life cycle, but European eels at all stages in their life can become infected by eating intermediate hosts such as crustaceans, snails, amphibians, insect larvae, and other fish. Dr. Jones says that studies on other local species affected by the worm could reveal much about the way it behaves in new environments.

Given the decline of eels in our waters and the potential for the spread of A. crassus, Dr. Jones warns that other sites are likely already infected or will soon become so. She emphasizes the need for a more extensive survey on the distribution of A. crassus throughout Cape Breton. The introduction of exotic species, she says, is increasing at an alarming rate, so it is important to study them at these early invasion stages.

For more information contact:

Dr. Martha Jones
Department of Biology
Cape Breton University
Sydney , Nova Scotia
B1P 6L2
Phone: (902) 563-1973
Email: .(JavaScript must be enabled to view this email address)