Science in Society Archive

Transgenic Fish Coming

Prof. Joe Cummins exposes the regulatory vacuum behind the rush for commercial release of transgenic fish

Glofish for the new year

The tiny zebra fish that lives in aquariums, a popular laboratory animal, was genetically modified to produce a fluorescent red pigment, and is being promoted for sale as a household aquarium pet, the "glofish". The glofish caused a stir in the United States because regulation of such transgenic pets is murky and none of the major regulatory agencies: FDA, USDA or EPA has been willing to take the lead in regulating the glofish (even though USDA does deal with pet animals). The glofish is set to go on sale January 5, 2004 without regulatory approval [1].

FDA announced [2]: "Because tropical aquarium fish are not used for food purposes, they pose no threat to the food supply. There is no evidence that these genetically engineered zebra danio fish pose any more threat to the environment than their unmodified counterparts which have long been widely sold in the United States. In the absence of a clear risk to the public health, the FDA finds no reason to regulate these particular fish."

The FDA position that transgenic glofish are substantially equivalent to unmodified fish is hypothetical and no effort has been made to test the transgenic fish in contained, but wild-like environments. Fish pigmentation with "poster" colors is an aphrodisiac to wild fish and may even provide protection from predators in certain light conditions [3,4], or the pigment fluorescence may signal toxic defence as in the stinging sea anemone from which the glofish transgene was prepared and in that way discourage predators.

FDA was presumptuous in washing its hands of the regulation of the transgenic zebra fish, which is likely to become a major pest of warm water areas.

Other transgenic fish to follow in droves

The release of glofish may signal relaxation of the regulation of transgenic fish now being promoted for commercial release. To ensure that transgenic fish do not overpower or seriously pollute the gene pool, both promoters and regulators stress the safety of "sterile" transgenic fish released to bodies of water. Previously, "sterile" fish are produced using synthetic triploid strains of fish produced from treatment of eggs pressure or temperature shock and with sex hormones. As I-SIS reported [5], the sterile triploids were "leaky" and tend to produce a few fertile progeny, which can establish transgenic populations.

In spite of these problems, the transgenic fish are being promoted as the first marketable transgenic animals for human consumption [6]. More effort seems to have been spent on promoting the existing defective transgenic fish than on improving them so that they can be safely released for commercial production. Muir and Howard [7] defined conditions under which transgenic fish can cause rapid extinction to wild fish stock, thus posing extreme risk; but this has been ignored in the rush to commercialization.

Development of transgenic fish has focused on a few species including salmon, trout, carp, tilapia and a few others. Salmon and trout are cash crops while the others primarily provide sources of protein. The salmon nearest to commercial release is the Atlantic salmon engineered with a pacific salmon growth hormone driven by the arctic antifreeze promoter gene [8]. The rapid growth of that transgenic salmon is achieved, not so much by the transgenic growth hormone as by the antifreeze gene promoter that functions in the cool water desirable for salmon flavor. The commercial release of transgenic salmon, even in somewhat contained fish farms, is likely to lead to problems similar to those experienced in the Atlantic salmon farms of the northwest Pacific. A number of studies indicate that salmon produced in sea pens escape and breed with native species, introducing new disease and spreading pollution from the culture pens [9,10]. These problems will probably be amplified in the fast growing transgenic stocks.

Tilapia fish, native to Africa, are cultured world wide as "poor man's food", second only to carp as warm water food fish, and exceeding the production of Atlantic salmon (whose market value is twice that of tilapia). Tilapia has been extensively genetically modified and promoted as a transgenic fish exclusive for isolated or contained production [11]. Transgenic tilapia, modified with pig growth-hormone, were three times larger than their non transgenic siblings [12]. Tilapia genetically modified with human insulin grew faster than non-transgenic siblings, and could also serve as a source of islet cells for transplantation to human subjects [13,14]. Trout growth hormone was used to produce transgenic carp with improved dressing properties. Such transgenic carp are recommended for production in earthen ponds [15].

Giant mud loach was produced by linking the mud loach growth hormone with its actin promoter. These giant fish are not, technically speaking, "transgenic", as they contain no foreign genes even though the inserted construct is artificial, and pose a paradox for regulators [16].

Silk moth genes were introduced into Medaka fish to create resistance to bacterial pathogens [17]. Some commercially desirable fish and crustaceans have been difficult to genetically engineer because embryonic tissue is difficult to manipulate. But it has been found that the parental gonads of such animals could be modified using replication defective pantropic retroviral vectors. Pantropic vectors can transform an array of species they are modified forms of the Moloney mouse leukemia virus used extensively in gene therapy. Such vectors have proven useful in modification of a range of edible marine animals including mollusks [18]. Animals produced using modified mammalian leukemia viruses will require extensive testing and long-term evaluation prior to release for human consumption. This is particularly important in view of the leukemia cases found among the handful of successes in human gene therapy, which were done with a retroviral vector (see "Gene therapy risks exposed", Science in Society 19).

Contained cultures of transgenic fish

The current generation of transgenic fish has not passed the test of complete sterility if released or escaped to the environment [5]. Fish production in inland earthen ponds may prove acceptable for contained transgenic fish culture. But such facilities should be provided with fail-safe destruction of the pond animals in the event of flooding and adequate protection from theft. Pond commercial culture is effective for carp and tilapia, but more difficult with salmon and trout. Currently, pond culture is suitable for carp and tilapia because the fish are vegetarians, carnivorous salmon and trout depend on a diet of fish and fishmeal but the worldwide stock of feed fish has diminished and suitable vegetable meat substitutes must be found [19]. Atlantic salmon (as typical cold water carnivores) cannot thrive on a diet of rapeseed oils but the fish can achieve maturity if finished with fish oils at least 20 weeks near the end of their maturity cycle [20]. GM oil rape seed with enhanced production of long chain fatty acids are proposed to serve as feed for pond cultured fish [21]. And glyphosate-tolerant GM canola meal has been pronounced substantially equivalent to non-GM canola as feed for rainbow trout [22].

Aquaculture can help feed the world without diminishing ocean resources, but premature releases of transgenic fish stocks will do more harm than good. Bad decisions have plagued aquaculture, resulting in pollution and extensive damage to native stocks. International agencies such as the World Bank, the International Development Bank and the Food and Agriculture Organization of the United Nations have created harm by ill- advised projects that led to damage to native resources and pollution. Scientists Julio E. Pérez and Mauro Nirchio of Venezuala along with Juan A. Gomez of Panama commented in Nature: "However, if the aquaculture industry is going to reduce the pressure on wild fish stocks and provide food for the world's growing population, substantial changes must be made by governments, the private sector and international funding agencies. They must protect coastal ecosystems; promote research and development of native species; and encourage farming of low-trophic-level fish — those low on the food chain. International technical funding agencies can exert great influence in changing practices" [23]. Without such constructive thinking, the aquaculture industry poses a threat, not only to ocean fisheries but also to itself.

Article first published 15/12/03


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