Date: 6 Jun 2003
From: Pablo Nart <p.nart_at_vet.gla.ac.uk>
Source: The Oregonian, 6 Jun 2003 [edited]
<http://www.oregonlive.com/metronorth/oregonian/index.ssf?/base/metro_north_
news/1054901093317960.xml>
A deadly virus has made its first appearance at the Vancouver Trout
Hatchery, a likely culprit in the die-off of 400 to 500 fish in a
month-long span. As many as 46 rainbow trout a day were dying at the
height of the outbreak. The numbers recently dropped to the single
digits after 422 trout died in May 2003.
Officials at the nearly 65-year-old hatchery, which raises 100 000
fish for release to the wild for the enjoyment of sport fishermen,
can count themselves lucky. Infectious hematopoietic necrosis virus
has been known to wipe out 90 percent of stocks at other hatcheries.
Eating infected fish is not harmful to humans, said John Kerwin,
hatcheries division manager with the state Department of Fish and
Wildlife in Olympia.
The virus, which has no cure, has been called the most significant
viral pathogen of salmon and trout in the Northwest.
The number of deaths at the hatchery is down to a few fish a day.
Biologists and others are taking steps in hopes of ensuring that the
virus does not return. And they're trying to determine how the
disease arrived.
Predatory waterfowl are at the top of Gary Vaughn's suspect list.
Vaughn is a Fish and Wildlife hatchery specialist based in Washougal.
He found about 16 dead trout at a release gate of Biddle Lake, a
1-acre holding pond where fingerling salmon grow before they are
trucked to stock area lakes.
"That's part of the problem right there," Vaughn said Thursday,
walking onto a Biddle Lake observation deck and pointing to a heron
perched in tree. Herons, cormorants, and other winged predators
feast on the lake's hatchery fish. Department rules prohibit killing
or harming the birds.
Under the scenario considered by Vaughn and others, a bird carrying
the virus pathogen could have tried to gulp a fish, regurgitated it
for some reason and dropped an infected carcass into the water.
Another possibility is that machinery, such as trucks that are shared
between hatcheries, could have introduced the pathogen to the
Vancouver hatchery, which is the only 1 in the city and 1 of 6 in or
near Clark County. Kerwin said that cause is unlikely, given the
department's protocols for cleaning machinery with bleach.
Stressed-out fish are more prone to contracting disease. Fish can get
frazzled if they're packed too closely or their environment is
polluted. Kerwin, who oversees 90 hatcheries in the state that house
125 million fish at a time, discounts those possibilities as well.
The pathogen is common in wild salmon stocks, particularly sockeye salmon.
"History tells us we'll find this virus every year in a group of
fish," Kerwin said.
He presided over a conference call Wednesday with about 6 other
hatcheries officials to discuss the Vancouver situation.
"As a group, we agreed to go forward to solve the riddle of finding
out where it came from. That's the big challenge." said Richard
Johnson, a state hatcheries complex manager in Washougal and a
participant in the conference call. The group also discussed what
steps to take to ensure that the virus does not reappear.
The hatchery, a 1938-39 Works Progress Administration project built
on the former site of a sawmill, is an integral part of the Columbia
Springs Environmental Education Center at 12208 S.E. Evergreen
Highway, east of Interstate 205. A partnership of agencies oversees
the center: the state, Clark Public Utilities, Vancouver, Clark
County, Clark College and Evergreen School District.
The virus episode points to the need for improved facilities at the
center, Johnson said. He would like to see construction of
meandering fish tanks, replacing Biddle Lake's role as the place
where fingerlings grow up, and removing the birds' easy pickings.
Construction of an education center near the site is on the wish
list, too.
But Johnson acknowledged that money is tight and doesn't anticipate
any of these changes happening soon.
[Byline: Allan Brettman]
- --
ProMED-mail
<promed_at_promedmail.org>
[Infectious hematopoietic necrosis is an acute rhabdovirus infection
most often in fry and fingerling salmonids. It produces high
mortality at water temperatures less than or equal to 12 deg C. Such
high mortality may have an economic impact in certain regions.
Affected fish darken, have pale gills, and shed thick fecal
pseudocasts. Both horizontal and waterborne transmissions have been
demonstrated. Asymptomatic carrier fish serve as reservoirs of
infection. - Mod.TG]
[see also:
2002
- ----
Infectious hematopoietic necrosis, salmon - USA 20020721.4825
1999
- ----
Infectious hematopoietic necrosis, fish - France 19990303.0306
1997
- ----
Infectious hematopoietic necrosis - Belgium 19970903.1879]
...................tg/pg/lm
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