Sterilized Frankenfish-Biotech Progress?

Sterilized Frankenfish-Biotech Progress?

New York Times
March 31, 2002
Genetic Engineering Rescues Salmon

For years, conservationists and green-minded scientists dedicated to
saving wild Atlantic salmon have sifted through predictions of juicy tomatoes the
size of beach balls and chickens consisting entirely of white meat, looking
for some shred of evidence that genetic engineering is not merely an upbeat,
artfully disguised and cheerfully publicized death sentence for wild creatures
as we know them.

They have not found much, not until the recent appearance on their
radar screens of triploid salmon. These are salmon that can be rendered
sterile, cheaply and efficiently, while they are still in the pre-embryonic,
egg stage of their development. If the sea farmers in the $600 million
commercial aquaculture industry can be persuaded to grow only triploid fish, one
of the most significant threats to the dwindling, stressed stocks of wild
salmon - the perils posed by mixing the genes of domestic and wild fish - can be

"This could be a win-win scenario," said Fred Whoriskey, vice
president of research and environment for the Atlantic Salmon Federation, "in that
taking the genetic, reproductive component in farm fish out of the picture in
a cost- effective way would really protect wild fish, while having just a
negligible effect on the salmon farming industry."

Triploid salmon, however, are not yet the magic bullet sought by a
conservation establishment that has been stung more than once by false hopes.

. . .

Only a few decades ago, it appeared that by accelerating the viability
and growth of fish-farming, genetic science would help lift the veil of
extinction slowly closing around wild salmon. If you could grow salmon as if they
were corn or chickens, the cost-intensive process of fishing on the high
seas for wild salmon would become economically unfeasible. Thus, conservation
groups, including the Atlantic Salmon Federation, enthusiastically supported
aquaculture. The industry, along with the science helping drive it,

"The salmon growers keep coming back to genetic programs with `we need
this, we need that,' " Whoriskey said. "It's really just like breeding dogs.
The genetics guys even select for body shape now, trying to increase the
boxlike shape of the fish to increase the marketable flesh and the ease with
which it can be packaged."

The X-factor that nobody anticipated was that farming on the ocean
proved more problematic and far less predictable than on dry land. The chief
problem was containment: sea cages were prone to destruction by storms and
predators, like seals. As the industry exploded, so did the numbers of increasingly
specialized fish that, while neither bred nor fit for life in the wild, retained
two important attributes of their wild cousins: the urge to ascend rivers
and the ability to reproduce.

When salmon-farm escapees mate with wild salmon that have evolved to
survive the rigors of nature (rather than to serve the needs of fish growers),
the gene pool of the wild, river-specific fish is severely compromised. Their
offspring may not have the genetic tools required to survive the complex,
demanding natural life cycle. Clearly, being shaped like a cardboard box does
not help a salmon leap a falls, or escape a predator.

Enter, triploids.

. . .

Whoriskey said the process of triploidization is a relatively simple
one that can be carried out upon hundreds of thousands of eggs at one time for
a fraction of a penny a fish. The fertilized eggs are put into an
enormous, high-tech version of a pressure cooker, and subject to a shock that so
disrupts cell development that each cell in the fish will subsequently have three
rather than the natural two sets of chromosomes (the diploid condition, similar to
our own).

These triploid fish will then grow normally until, as a prelude to
reproduction, they begin to develop protosperm and egg cells. When
those cells are about to divide, automatically delegating either side of the cell
for one of either set of chromosomes, the existence of the third set confuses
the cell. "The machinery is designed to deal with two, not three sets of
chromosomes, so the works get gummed up and the whole process falls apart," Whoriskey
said. "The fish is unable to generate sperm or egg cells."

But so far, four factors, influenced by economic problems like
shrinking prices - and profits - in the aquaculture industry, have kept fish farmers
from embracing triploid salmon.

. When approaching reproduction, healthy salmon experience a growth
surge. Because they are sterile, triploids do not. In early experiments,
triploids were up to a third smaller than wild, sexually capable fish of the
same strain.

. Although triploid fish in theory contain more protein (the extra DNA
in the third chromosome), food processors have objected that the cells of
triploid fish are larger and thus have a higher water content, making them less
desirable as consumer products.

. In some strains, triploids have shown a higher than acceptable rate
of some developmental deformity, like a jaw that juts out in the wrong
direction. While strictly cosmetic, such abnormalities are anathema to fish buyers -
and consumers.

. The immune systems of triploids appear to be weaker than those of
diploid fish, wild or otherwise.

Researchers are working, with some success, on diminishing these
drawbacks. If they do, it will be a sorely needed triumph for conservationists still
waiting to see if the vision of genetic futurists is broad enough to include
the survival of salmon that are not shaped like boxes.

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