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July 24, 2000


Transgenic "Superfish"


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Greg Conk wrote:

Date: Jul 21 2000 09:54:36 EDT
From: Greg Conko
Subject: Superfish are no superfix; Question

Jean-Michel Cousteau Watch: Superfish are no superfix for hunger -
7/20/2000 - Features - Environmental News Network - Your leading news
source on the environment From the Environmental News Network

Highlights from ENN article (full text below): "William Muir and
Richard Howard of Purdue University discovered that more than 30
percent of Japanese medaka born with the hGH gene did not live to
sexual maturity. ... [I]n nature, surviving to sexual maturity is
everything. The superfish may dominate the mating game, but if they
are least likely to produce viable offspring, the population will
eventually decline. ... Purdue scientists calculated that if 60
transgenics were released into a population of 60,000 wild fish, it
would only take 4 >generations for the species to become extinct."

QUESTION: Has anyone read this paper? If the "superfish" are least
likely to produce viable offspring, as the article suggests, would
that not be its own selection pressure to slowly reduce the
occurrence of the gene, or reduce expression of the phenotype, in
wild populations? The superfish would be more likely to mate than
non-transgenic fish, reducing total populations in the short term,
but would this effect really last 40 generations?


I'd like to respond to this, and maybe others can help out. First,
let me say that I am not an expert in fish breeding or aquaculture,
but when I read the ENN Jean-Michel Cousteau story on the
Environmental Network News webpage, I was concerned because the
description of the properties of the transgenic salmon in that story
seem to be at odds with what the producers of the fish are saying. I
have attended two oral presentations on this transgenic salmon at
scientific meetings in the last 5 weeks (ABIC-2000, Toronto, June
5-8, 2000: AquaAdvantage Salmon: Issues in the Introduction of
Transgenic Food, E. Entis; and The Biosafety of Genetically Modified
Organisms, Saskatoon, July 9-13: Current Status of Transgenic
Atlantic salmon for Aquaculture, G. Fletcher et al. --A brief paper
is available in the Biosafety conference proceedings). My comments

1. We are told in the opening paragraph: "Behold the "superfish," a
salmon that grows six times as fast and twice as large as normal
farmed Atlantic salmon but only consumes three-quarters as much feed
before it is brought to market."

The fish do not grow to 2X size, in fact, they grow only to nearly
the same size at sexual maturity as conventional salmon because
growth slows as they reach maturity. The developers have never
claimed otherwise. Market weight is 3-4 kg.

They do not grow at 6X the rate either, although the developers do
say 3-6X, what I saw in their data was that most fish grow at 2-3X
for a few months--the observed rate does, however, depend on the size
of the interval one chooses. If one chooses the interval between
hatching and reaching market weight, the acceleration of growth is
less than two-fold in most cases. The idea is simply to bring fish
to market one year sooner than the conventional fish, which is far
more economical (profitable) because it is not only more feed
efficient but it also offers the possibility of eliminating culture
over one or more winters which result in slow growth and increased

2. Citing Purdue's Muir and Howard, as noted in Greg Conko's
posting, the story suggests: "The superfish may dominate the mating
game, but if they are least likely to produce viable offspring, the
population will eventually decline. " The salient point here is that
as they approach sexual maturity growth rates slows such that
conventional and transgenic fish mature at nearly the same size. At
sexual maturity the transgenic salmon are, on the average, slightly
smaller--presumably because of their rapid growth. This means that
the transgenic fish have no selective "advantage" as the story
suggests. Muir and Howard would probably be the first to admit that
their theoretical projection does not apply if the fish are the same
size at maturity. And, it should be noted that they have published
only a theoretical calculation that has never been tested in a real
ecosystem where many additional variables such as limited food
supply, competition, weather, disease, and predation-- to name few of
hundreds of factors-- will modulate the outcome.

3. The story goes on to say: " Advocates of genetic engineering
maintain that these fish can be rendered sterile and isolated from
wild populations. Both contentions are dubious.

Complete sterilization of all fish is simply not a reality. Nor is it
likely to be. No company has stepped forward to guarantee 100 percent
perfection in sterility. And nothing short of perfection is
acceptable, for it only takes one well-endowed superfish in a
population of wild salmon to start the process of decline."

I would welcome some population geneticists to evaluate the unproven
assertion that one "well-endowed superfish" could "start the process"
of decline." Perhaps someone could tell us if a single "super" gene
in a local population would flourish or be washed out. The producers
claim that even if one grants that 100% sterilization is not
possible, they have not observed a single fertile fish in 20 years
(thousands of fish) of producing triploids. There is a middle
ground between absolute certainty of sterility and total fertility
that is sufficient to insure gene containment. It's a function of
the effectiveness of sterilization and the numbers of fish produced
(a probability calculation), but it also means that we are ASSUMING
escape (see below). Transgenic salmon will have a male phenotype and
a female genotype with no Y chromosome. These fish display no male
mating behaviors and do not return to rivers to mate. And, if the
fish exhibit no male mating behavior, the point regarding gene escape
is moot.

What about containment that the author says is "dubious?" While the
author does not provide any evidence or studies to support his claim
that they won't be 100% sterile and can't be contained, he also
discounts the feasibility of the most effective containment method.
The developers of the transgenic salmon specify that the fish should
grown in inland pounds, even though they will be triploid sterile
females. The developers believe that land-locked pounds are
becoming an economically viable option. They have not proposed to
release them or culture them in the sea in net containments. It is
also noteworthy than salmon production in inland pounds lessens the
environmental impact of raising fish in net cages in fragile
coastline ecosystems.

4. Another interesting point I picked up along the way is that the
transgenic salmon may in fact be at a competitive disadvantage in the
wild for two reasons: 1) its higher food demand forces it to need a
constant supply of food which may not be available in the wild (I
would conjecture that the fish may not exhibit the rapid growth
phenotype in the wild where food supply is limiting), and 2)it has a
potentially fatal disregard for predators. Behavior studies have
demonstrated that the transgenic fish are more interested in feeding
than conventional fish and do not hide or run in the presence of a
predator--they instead continue feeding. Maybe bigger isn't always
better or smarter!

5. The story about the superfish goes into some length to explain
why transgenic salmon won't feed the world. For what it's worth, I
never heard the company claim that their fish would feed the world.
They developed their fish so that they could get more salmon to
market sooner in order to make a profit, provide a more plentiful and
less costly supply to consumers, and to offer remediation of some of
the environmental impact of coastal salmon farming. At no point did
I hear them claim any motive other than the profit motive. They
probably know that the developing world will not buy their salmon,
and cannot and will not buy their technology. Most of the developing
world is inappropriate for salmon farming. I suppose there is some
small chance that the development of transgenic salmon will inspire
scientists in developing countries to construct their own transgenic
species for similar goals. This is in part facilitated by the fact
that the developers have openly publicized their methods and results.
So, at the end of the day, even if we agree with what has been said
about the reasons for and solutions to hunger in the story, hunger
and the solution to world hunger has little to do with transgenic
salmon. I suppose all of this is to say that I agree with the thesis
that: "Superfish are no superfix for hunger." To my knowledge,
however, that has not previously been a requirement for a new product
to be brought to market.

There have been quite a few stories in the press about "superfish"
that claim gigantic salmon will be the result of stimulation of
growth hormone production. Claims of fish weighing 200 lbs, 300 lbs,
and even 1200 lbs abound. These claims are a far cry from a 4 kg
market fish. This kind of fictional exaggeration, while at first
amusing, is not funny because it impedes serious discussion of
legitimate concerns and issues. What is required to assess the
safety of this product, as with any other, is careful and unemotional
review of the relevant data on food and environmental safety by
regulatory agencies as is now being done. Regulatory approval cannot
be presumed at this point, but if it comes it should and will be
based on solid scientific evidence. It will nonetheless be difficult
to explain that to consumers when they have read about 200 lb
superfish -- aberrant "creatures" that are about to take over the

Let me close by noting that one of the objectives in conventional
animal breeding is to obtain
animals that grow more rapidly and consequently get to market faster.
It is paradoxical that selection of a strain of salmon with mutations
in the growth hormone promoters and enhancers could some day produce
a salmon bearing the same accelerated growth properties. Since it
will not be considered transgenic because it was not produced by the
insertion of a promoter from another specie of fish, it will require
no regulatory approval. We are told "... it only takes one
well-endowed superfish in a population of wild salmon to start the
process of decline." One has to ask if such a fish appeared by
spontaneous mutation in a wild ecosystem, would Jean-Michel Cousteau
even choose to use the word "decline?"

Bruce M. Chassy
Assistant Dean for Biotechnology Outreach, Office of Research
College of Agricultural, Consumer and Environmental Sciences
Executive Associate Director, Biotechnology Center
University of Illinois at Urbana-Champaign

238 NSRC
1101 West Peabody Drive
Urbana, IL 61801 b-chassy@uiuc.edu