A discussion on the NANFA
e-mail list, introduced by Jay DeLong (WA), reinforced the reasons
why we can't release any fish back into the wild after it has
been maintained in captivity: frog and toad populations can suffer.
A decline in anuran (frog and toad) populations has been noted
around the world. Many theories for the decline, ranging from
disease to habitat degradation, have been discussed with varying
degrees of blame attributed to each. A team of researchers from
Oregon and Pennsylvania State Universities has thrown a new theory
into the mix. The new theory involves a fungus, Saprolegnia ferax,
being fatally spread to anuran populations by hatchery reared
fish. A similar idea was introduced to explain the decline of
Australian rain forest frogs where the most likely culprit was
a virus introduced via imported aquarium fish. The fungus appears
to be on the fish's scales or in their mucus layers and is introduced
when the fish are released. Laboratory research showed a 15 percent
increase in toad egg mortality when toad eggs were exposed to
infected rainbow trout. The fungus lives on the outer membrane
of the toad embryo and as it grows, it ruptures the membrane
and smothers the embryonic toad. How big of a potential problem
is this? Hatchery reared fish have been introduced into nearly
half of the 16,000 mountain lakes in the western U.S., including
a large number of lakes in national parks and wilderness areas!
The popularity of fishing makes it difficult to discontinue stocking
with hatchery reared fish, but this is one of those areas where
biologists and economists and everyone involved must examine
the potential environmental costs of their activities.
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