Daily Invader

Chesapeake Bay Diseases and Parasites

Eel Swimbladder Nematode (Anguillicoloides crassus)


Eel Swimbladder Nematode (Anguillicoloides crassus) arrived by ship.






The Eel Swimbladder Nematode is native to Japan and coastal China, where it is a widespread and common parasite of the Japanese Eel (Anguilla japonica). In the 1980s it was found in European Eel (Anguilla anguilla) in Germany, where it was likely transported with shipments of live Japanese Eel. From this early introduction and many secondary introductions, the parasite spread all across Europe. The parasite was first discovered in North America at an aquaculture facility in south Texas, but soon was seen in many other areas including the Chesapeake Bay. In the Chesapeake Bay ballast water is a likely vector for transport of this parasite, because copepods, the nematode’s most frequent intermediate host, are often seen in samples of ballast water about to be discharged into the Bay. Eels get the nematode by eating copepods and other crustaceans that have already eaten the larvae. When the nematode larvae are eaten by the eel, they make their way to the eel’s swimbladder where they grow into reproducing adults. Adult nematodes release their larvae into the swimbladder. The larvae leave through the pneumatic duct into the water where they can again be eaten by copepods. American Eels (Anguilla rostrata) in some areas of the Bay have high infection rates, but given the eel’s migratory lifestyle, it’s difficult to know if this plays a role in its declining population. Complete Record 


MSX, Delaware Bay Disease (Haplosporidium nelsoni)


MSX, Delaware Bay Disease (Haplosporidium nelsoni) may have been spread by multiple vectors. 




MSX, Delaware Bay Disease, is a parasite of the Eastern Oyster (Crassostrea virginica) and first appeared in Delaware Bay in 1957 and in Chesapeake Bay in 1959. There is evidence the disease came into the US with infected Pacific Oysters (C. gigas) imported from Japan. MSX is a haplosporidian parasite of the Pacific Oyster in its native range (Asia) and recent immunological comparisons between MXS in Korea and Chesapeake Bay found the two to be nearly identical structure and immunological responses. Between 1930 and 1970 there were several unofficial plantings of Pacific Oysters along coastal New Jersey, Maryland, and Delaware. None of these introductions resulted in established populations of the oyster, but the appearance of MSX in 1957 may have been an unintended result of these introductions. We can’t be sure that this was how MSX was imported to the US, however, and given the increase in ship traffic in the region, oysters in hull fouling or spores in ballast water are also possible vectors. Nonetheless, the disease has had a devastating impact on the native Eastern Oyster and caused massive die-offs, and is at least partially responsible for decline in oyster harvest between 1957 and 1970. Complete Record 


Mud Crab Parasitic Barnacle (Loxothylacus panopaei)


Parasitic Loxothylacus panopaei inside the abdomen of a white-fingered mud crab (sac indicated by arrow). 







Loxothylacus panopaei is a parasitic barnacle, which surprises many people because the adults look nothing like a typical barnacle. This species is highly specialized and adapted to live in and on mud crabs. The female parasite infects recently molted crabs by burying into the carapace and preventing the crab from reproducing. Once inside the crab, she forms a sac protruding from the crab's abdomen where several broods of thousands of larvae each are produced. These sacs are the only visible sign of the parasite. The parasite was first described in 1884 on crabs from Tampa FL, where they are native. Their native range includes the Gulf of Mexico, the Caribbean, and the Atlantic coast to Cape Canaveral, FL. They are parasites on many species of mud crabs throughout this range. Mud crabs are easily transported with oysters and the barnacle was likely introduced by infected mud crabs caught up in shipments of oysters from the Gulf of Mexico. The first discovery of the parasite in Chesapeake Bay was in 1964 when the parasite was found on the native White-fingered Mud Crab (Rhithropanopeus harrisii) in the York River. The parasite is now common in much of the Bay but the population and abundance varies greatly between years. Surveys in 2010 saw a relatively high abundance of the parasite in several locations on the Eastern Shore of Maryland. Since this barnacle prevents mud crabs from reproducing, it probably affects their populations, but, it's hard to know for sure, because they are very hard to count. Complete Record


Whirling Disease (Myxobolus cerebralis)


Whirling Disease (Myxobolus cerebralis) is fish parasite to native central Europe. 

Whirling Disease is a trout and salmon parasite discovered in 1893 when Rainbow Trout, a native to the Pacific coast of North America, were imported into Germany and contracted the disease. The parasite is probably associated with the Brown Trout, which is native to central Europe and Northeast Asia. The parasite was spread as Brown Trout and others fish species were moved around the world as part of the push to enhance sport fishing. The disease is especially common in hatcheries and has been seen in several in Virgina and Maryland, but is also widespread in natural waterways. The disease causes the skeleton of juvenile fish to curve, which causes the fish to swim in a circle or whirl. Complete Record 


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