- New research shows that hatchery-reared fish can spread
a fungus implicated in the mass deaths of amphibian embryos in the Pacific
Northwest. This is the first evidence that fish- stocking can spread amphibian
diseases.
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- "Fish used in stocking programs could be important
vectors for diseases responsible for amphibian losses," say Joseph
Kiesecker of The Pennsylvania State University in University Park and his
colleagues in the August issue of Conservation Biology.
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- Historically, hatchery-reared fish were introduced to
nearly half of the 16,000 mountain lakes in the western contiguous U.S.
Today, fish are still stocked in a number of national parks and wilderness
areas. Fish stocking is common at Pacific Northwest sites with mass amphibian
deaths, and the associated fungus (Saprolegnia ferax) is a common disease
of hatchery-reared fish.
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- To determine whether fish-stocking could spread the fungus
to amphibians, Kiesecker and his colleagues collected rainbow trout from
a fish hatchery and freshly-laid western toad eggs from Lost Lake, Oregon.
Western toads have declined severely since the late 1980s, and up to 90%
of the toad embryos have died at sites with Saprolegnia outbreaks.
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- Laboratory experiments confirmed that trout can spread
the fungus to toad embryos: exposing the embryos to infected trout increased
their death rate by about 15%. The researchers also found that trout can
spread the fungus to soil, which can then infect toad embryos. This treatment
also increased the embryo death rate by about 15%.
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- While the death rate of fungus-exposed embryos is much
smaller in the laboratory than in the wild, this is due to the fact that
being exposed to the fungus is not enough to cause an outbreak. Kiesecker
and his colleagues had previously shown that UV-B radiation also plays
a role in Saprolegnia outbreaks.
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- The researchers caution that discontinuing fish-stocking
may not be enough to control diseases spread by introduced fish. "If
introduced pathogens become established, effects could persist even after
fish stocking has been discontinued," say Kiesecker and his colleagues.
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- Kiesecker's co-authors are: Andrew Blaustein of Oregon
State University in Corvallis and Cheri Miller of Alexion Pharmaceuticals
Inc. in New Haven Connecticut.
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- For more information about the Society for Conservation
Biology: http://conbio.net/scb/
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