Mich. (AP) - Subtle immune system changes may explain why some Great Lakes
trout and salmon die from the lack of an essential vitamin after eating
alewife, an important forage species, according to a scientific report
deficiency of thiamine, or Vitamin B1, is a primary obstacle to restoring
lake trout, which were decimated by parasitic sea lamprey in the mid-1900s.
It also hampers the stocking of chinook and coho salmon, popular sport fish
native to the Pacific that were introduced into the Great Lakes in the
Thiamine is needed
for cell energy production and nerve function and is an antioxidant, meaning
it can delay or prevent some types of cell damage.
Some fish hatch
from eggs that were low in thiamine to start with, resulting in die-offs
known as “early mortality syndrome.” Operators of Great Lakes trout and
salmon hatcheries bathe young fish, or “fry,” in thiamine solutions to help
them survive after being released to the wild.
But when they get
large enough, they begin feasting on the alewife, an invasive fish believed
to have reached the lakes through the Erie Canal and the Welland Canal that
connects Lake Ontario and Lake Erie. Alewives carry an enzyme that destroys
worked for years to understand the mechanisms by which alewife consumption
kills sport fish. In the new report, published in the journal Fish &
Shellfish Immunology, researchers said lake trout deprived of thiamine were
exhibiting immune system changes similar to those in humans with
That suggests those
fish have increased susceptibility to ailments such as bacterial kidney
disease, a leading killer of chinook and coho, said Christopher Ottinger of
the U.S. Geological Survey, lead author of the report. While the study
focused specifically on lake trout, it’s likely that the findings apply to
salmon as well, he said.
represents another step in piecing together the complex processes that can
harm species playing central roles in Great Lakes food chains and the
region’s $7 billion sport fishing industry.
“It becomes part of
the picture about restoration of lake trout in the Great Lakes,” Ottinger
said. “It helps managers look at their options and come up with solutions
that best meet their needs.”
that the study provides no simple answers to the thiamine deficiency
problem. Reducing the alewife population would deprive trout and salmon of
an important food source.
complication is that thiamine deficiency levels can fluctuate from year to
year, making it hard to determine proper water treatment levels, said Steve
LaPan, head of the New York Department of Conservation’s fisheries section.
Its Lake Ontario program applies thiamine treatments before the lake trout
eggs hatch in hopes of catching the problem early.
Randy Claramunt, a
fisheries research biologist with the Michigan Department of Natural
Resources, said the study reinforces the importance of diversity in predator
and prey species. Fisheries managers have made progress in restoring cisco,
a native prey fish, in parts of the Great Lakes as an alternative to
also is coming from another invasive species - the round goby, which arrived
in ship ballast in the 1990s. Not only does it gorge on pesky zebra and
quagga mussels, but it provides a food source for trout and salmon.
Yet the round goby
also has a downside. The mussels it eats are believed to carry botulism,
which is killing loons and other aquatic birds that feed on gobies.
“All of this is
reflective of the substantial changes happening in the Great Lakes from
invasive species,” Claramunt said.