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Topic Review (Newest First)
07-23-2001 09:07 AM
John Desjardins
A potential problem with stocking I've never heard of before.

I saw the following press release this morning while doing my regular check for info of interest for work. I'd never heard much about the potential of stocking to transfer diseases between species. Anyone have more info on this topic?

John Desjardins

Contact: Joseph Kiesecker
Society for Conservation Biology

Fish-stocking may spread amphibian disease

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.

"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.

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.

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.

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%.

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.

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.


Kiesecker's co-authors are: Andrew Blaustein of Oregon State University in Corvallis;
and Cheri Miller of Alexion Pharmaceuticals Inc. in New Haven Connecticut.

Please mention Conservation Biology as the source of these items.For faxes of
papers, contact Robin Meadows

For more information about the Society for Conservation Biology:

*Joseph Kiesecker (814-865-8778 or -8779, *Andrew
Blaustein (541-737-5357,

*Joseph Kiesecker has scans of breeding pairs of western toads, and healthy and
infected western toad embryos.

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