Atlantic salmon may be screened for disease
The discovery that Atlantic salmon in two New England rivers, including the Merrimack, have been exposed to a deadly salmon virus is prompting federal officials to take precautionary steps to prevent further infection.
Scientists at a federal research laboratory recently reported finding antibodies for the infectious salmon anemia (ISA) virus. It was in blood serum taken between 1995 and 2002 from 10 salmon caught in the Merrimack River and four salmon from Maine's Penobscot River.
The tests were done on salmon brought to federal fish hatcheries as part of the program to return salmon to the Merrimack, Penobscot, and Connecticut rivers.
Salmon, which as anadromous fish spend part of their lives in fresh water and part in the ocean, were historically present in those rivers. But they were eliminated in the Connecticut and Merrimack rivers and significantly depleted from the Penobscot due primarily to the loss of spawning habitat that resulted from dam construction.
ISA primarily affects Atlantic salmon, according to the US Fish and Wildlife Service. The infection can be fatal to the fish, but the virus poses no threat to human health, said Dan Kuzmeskus, chief of the Division of Hatcheries for the Fish and Wildlife Service's northeast region.
Kuzmeskus said the recent test measured only whether the fish had been exposed to the virus. He said as yet there have been no cases of diseased fish found at any of the federal hatcheries involved in the salmon restoration program. But he said, ''With a disease that can be fatal and is known to cause significant mortalities, we are taking a precautionary approach," noting that an outbreak of the disease ''could be a serious threat to our restoration program."
As one part of that effort, the service is looking to expand the disease screening of salmon that are brought to the hatcheries, according to Kuzmeskus, noting that step will require additional funding. He said it also is planning to continue the policy of isolating incoming fish until they are determined to be disease-free.
The disease was first noted by Norwegian aquaculture, or fish farm, operators in 1984. It was later reported by fish farmers in a number of countries, including Canada, where it caused a significant number of fatalities in 1996.
In 1999, the virus was detected in sea-run or wild salmon in southern New Brunswick. In 2001, sea-run salmon from the Penobscot River were found to have been exposed to the virus. That same year, the first confirmed case of the disease in the United States was reported at a Maine fish farm.
More than a million salmon at fish farming pens in Scotland, Canada, and Maine have been destroyed in an effort to contain the spread of the virus, according to the Fish and Wildlife Service.
The recent test was carried out at the US Geological Survey's National Fish Health Research Laboratory at the Leetown Science Center in West Virginia. In all, tests were done on stored serum samples from 450 Merrimack Valley salmon and 304 Penobscot River salmon. A total of 304 Connecticut River salmon also were tested, with none of them showing exposure to the virus.
Caleb Slater, leader of the anadromous fish project for the Massachusetts Division of Fisheries and Wildlife, said the precautionary steps that are being undertaken by the federal government make sense. But he said he does not believe there is a cause yet for concern about the disease infecting sea-run salmon.
