Japanese Worms Listen to the program: Program aired on May 31, 2001 and 2002. To listen to the program, you need Real Player. Click on the Real Player image for a free download. Another foreign species from ship ballast water threatens the Chesapeake Bay. The culprit is a blood-feeding worm from Japan known as Anguillicola crassus (sp). Historically found in Japanese eels, this parasite is rapidly infecting American eels in the Chesapeake Bay. One recent survey of 200 eels from the Potomac River found almost 90 percent were infected with the Japanese worm. With eel populations already in decline, scientists worry that infected eels might have trouble migrating to the Sargasso Sea near the Bahamas to spawn. Studies have documented that the Japanese worm significantly decreases the swimming performance of American eels. | Background info | References and further reading |

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Catadromous eels

American eels are catadromous, which means they live their life in freshwater but breed in the ocean. This is the other way around from anadromous fish like the striped bass and salmon that live in the ocean but return to freshwater to spawn.

A young eel is born in the Sargasso Sea, an area north of the Bahamas. The small larvae, called leptocephalus, don't swim but drift with the ocean currents for 9 to 12 months before they reach the coastal waters of North America.

Picture: American eel. Picture courtesy of U.S. Fish and Wildlife Service/Duane Raver.

The eels develop into "glass" eels before entering the brackish waters and freshwaters where they will live most of their lives. When the eels are around 1 meter (about 3 feet) long, they mature and get ready to migrate back to the Sargasso Sea where they will spawn. After spawning, the adults die and the larvae again drift north.
(For a picture of a glass eel or a map of their journey, visit Counting Virginia's Juvenile Eels.)

The parasite that is infecting the American eels is a small nematode called Anguillicola crassus. The nematode was first found in the swimbladders of the Japanese eel, and the worm is widespread in Japan along China's coast. Probably transported with commercial shipments of live Japanese eels, the nematode first arrived in Europe and later in the United States. In the summer of 1997, scientists found Anguillicola crassus in the Wye, Sassafras, and Patuxent Rivers in Maryland. Another survey showed a 90 percent infection rate for eels from the Potomac River.

References and further reading

• Information about Anguillicola crassus comes from the invasive species database of the Smithsonian Environmental Research Center (SERC) Marine Invasion Research Laboratory.
  
• The Watershed Radio program Hitchhikers discusses invasive species and the research of the SERC) Marine Invasion Research Laboratory.
  
• Members of the American Eel Monitoring Survey team at the Virginia Institute of Marine Science (VIMS) are counting the number of young eels that are migrating into Virginia's estuaries and freshwater lakes and pond. Their website has some great images of eels in various life stages.
  
• Read more about the American eel and its life cycle on the website of the The Chesapeake Bay Program.
  

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