MIT Sea Grant Center for Coastal Resources


Crassotrea virginica
Crassotrea virginica, the native oyster in Massachusetts
Aquaculture is the marine or freshwater equivalent of farming, where aquatic organisms are held under controlled cultivation and raised for food, ornamental or scientific uses. Salmon, shrimp, oysters, quahogs, mussels, and algae are examples of marine aquaculture species. Unfortunately, many species adaptable to aquaculture are not native to the area where they are cultured. These species may escape and compete with native species, or carry diseases and parasites that can infect local populations.

What are the impacts of escaped aquaculture species?

Most aquaculturists are careful not to release exotics into new environments. However, unintentional releases do occur. In the Northwest, Atlantic salmon have escaped through holes in net pens, and have been captured by commercial fishermen. There is concern that they may compete for food or nesting sites with native Pacific salmon.

In Massachusetts, introductions of American oysters, Crassostrea virginica, from the Mid-Atlantic region, carried a protozoan parasite, Perkinsis marinus, also known as "dermo". The parasite infects the digestive system, gills and mantle, and eventually kills the oysters. Other oyster diseases, including MSX, caused by Haplosporidium nelsoni, and juvenile oyster disease have caused widespread economic damage to both wild fisheries the aquaculture industry, and are easily spread by moving infected seed between growing areas. For these reasons oysters may not be relayed from infected areas, and hatchery stock for planting in Massachusetts is limited to certified Northeastern hatcheries. Policies and regulations may be different in other states.

Non-native oyster species have been introduced into the U.S. with variable results. The Japanese oyster, Crassostrea gigas, has out-competed and displaced native oysters in the Pacific Northwest, and the European oyster, Ostrea edulis, has gained a foothold in the Northeast, although occupying a different niche than the native oyster population. Other ecological interactions, however, may be less obvious, and yet to be determined.

The home aquarium trade and increased interest in garden ponds have greatly increased the importation and culture of exotic ornamental species. Intentional and accidental releases have caused serious problems, especially in southern areas, where tropical species can survive and reproduce.

What can we do about the problem?

Many states regulate the importation of living marine organisms. Permits or licenses are required that allow a review of the proposed activity, site and species for adverse affects and unwanted releases. In many cases, the organisms are grown in "closed" systems, where waste waters are recirculated and/or treated before released to the environment. In most cases, exotic species are not allowed to be grown or maintained where escapes are possible or local populations may be infected. Genetically altered organisms which are sterile may also help to reduce risks, but not eliminate them completely. Policies and regulations need to be updated as new information is discovered.

To find out about New England states' programs see policies and regulations. Individuals can also help, by never releasing any plants or animals to the environment. Ask your dealer about the species you purchase, and share your concern about preventing unwanted introductions. Insist on using only local plants (fresh or marine) in your aquarium. Do not release organisms purchased from pet and aquarium stores to the wild.

Aquaculture References


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  this page last updated on: 4 December, 2002