Status of Development of
Transgenic Aquatic Animals

ERIC HALLERMAN / ISB News Report Apr03

Atlantic salmon expressing a growth hormone (GH) transgene may become the first genetically engineered animal approved for commercial food production1. With 4–6 times the growth rate and a 10–20% improvement in feed conversion efficiency relative to non-transgenic salmon, production of the transgenic line offers shorter production times, reduced costs, and improved profitability to aquaculturists2. However, the transgenic salmon also pose food safety and environmental concerns3-5. With other transgenic fish likely to enter the regulatory system within the foreseeable future, a review of issues posed by development of transgenic aquatic species is timely.

Scope of research and development effort
The AquaBounty Atlantic salmon is the most widely publicized example of a large international effort aimed at developing transgenic aquatic and marine organisms (Table 1).

Table 1. Scope of effort for development of transgenic aquatic animals.

Species		Transgenes		Countries
Grass carp	Marker genes		US
Common carp	Growth hormone		Canada
Goldfish	Antifreeze polypeptide	Cuba
Wuchang fish	Ceciopin		UK
Giant loach	Interferon		France
Northern pike	Phytase			Norway
Rainbow trout	Human clotting 		China
		  factor VII 
Coho salmon	Reporter genes for 	Japan
Atlantic salmon   contaminants		Korea
Arctic charr	GnRH antisense		India
Mummichog				Israel
Striped bass
Largemouth bass
Walleye
Brine shrimp
Red swamp crayfish
White shrimp
Freshwater prawn
Japanese abalone
Red abalone
Blue mussel
Eastern oyster
Pacific oyster

The most frequent application is for food production; GH genes have been inserted into over a dozen species4. Cecropin6, interferon, and other genes have been introduced to increase non-specific immunity to disease. Transgenic zebrafish, medaka, and other species are used as model systems for research on gene expression and embryological development. In a recent application, tilapia were engineered for use as bioreactors to express human coagulation factor VII in their blood7. Transgenic fish are under development for environmental biomonitoring, for example, for detecting environmental mutagens8. Several research groups are experimenting with transgenesis as a means of achieving reproductive confinement9. Development of transgenic mollusks and crustaceans is complicated by the inability of many P0 founders to transmit the transgene5, although some progress has been achieved10.

Most transgenic lines are still in the development stage, although several are nearing readiness for possible commercialization. In addition to their possible benefits, the commercialization of transgenic aquatic organisms also poses a range of controversial issues, including food safety, environmental safety, and public policy.

Food safety
Foremost to many prospective consumers is the issue of food safety3,4. Although cooking and digestion would break down most transgene products, three types of food safety concerns must be considered. First, bioactivity of the transgene product may pose concern, especially for pharmaceutical proteins. Second, allergenicity may prove hard to assess if the transgene comes from a non-food organism. Allergenicity assessment will be somewhat easier if the transgene comes from an organism representing known allergenic food groups, including fish and shellfish. In that case, the transgene product can be tested for reactivity against antisera from individuals with known food allergies. Third, toxicity potential is relatively easy to assess, and toxin genes would not be candidates for gene transfer.

The National Research Council (NRC) found that the level of food safety concern posed by products of animal biotechnology varies with the application3. For fish expressing a GH transgene, neither GH, GH fragments, nor hormones secreted in response to GH pose a risk to the human consumer. Hence, GH salmon likely pose little or no food safety risk. A comparative analysis of composition of products from GH and non-transgenic salmon is ongoing2. The NRC has a broader study ongoing on unintended health effects of genetically engineered foods.

Environmental safety
A second set of issues concerns the environmental safety of aquatic GMOs. Escape from production facilities, such as floating net pens used for production of salmon, is likely. Interbreeding with wild populations poses genetic and evolutionary risks. Ecological risks are posed with a variety of species in the receiving ecosystem. The NRC attached a high level of concern to possible environmental impacts of transgenic fish3.

If transgenic individuals were to escape from confinement and interbreed with wild fish, would the transgene be purged from the population or would it persist? Empirical observations of particular transgenic lines3,5 show higher oxygen consumption rate, lower critical swimming speed, higher willingness to risk exposure to predators, and lower viability of young. These observations suggest that transgenic individuals are less fit than non-transgenic individuals, that selection would remove the transgene from the receiving population, and that genetic impacts would be minor. However, some researchers question whether selection would remove the transgene from the population rapidly enough that impacts would be minor, and question the impact of recurrent introduction of transgenes into the population. Further, some researchers argue that single-trait models are simplistic, and that we must consider how the transgene affects fitness through the entire life cycle. For example, would a gain in mating success due to large size of a GH transgenic fish come at the cost of juvenile viability11? Two net fitness models11,12 predict that when there are tradeoffs in fitness traits through the life cycle, the transgene could spread through the population and, under certain conditions, threaten the viability of the population. Other possible tradeoffs would include: increased male mating success and reduced adult viability; increased adult viability, and reduced male fertility; and increased male mating success and adult viability but reduced male fertility. Current knowledge of possible genetic impacts of transgenic aquatic species is such that we cannot predict the outcome should a transgene be introduced into a wild population.

Since possible genetic impacts are plausible, reproductive confinement is appropriate. The proponents of the transgenic Atlantic salmon suggest production of all-female triploid stocks2. This raises questions of whether 100% triploidy can be reliably achieved at the scale of commercial production and the level of sampling needed to assure that production stocks are indeed all triploid. The NRC is conducting a study of bioconfinement that should be helpful in addressing these questions.

Even with effective reproductive confinement, transgenic aquatic species pose ecological impacts on receiving ecosystems. Two key concerns are competition with and predation upon natural populations. Many interactions among aquatic species are mediated by size, particularly predation. We must determine for each case whether transgenics will exhibit a larger size distribution than non-transgenics. Ecological impacts can cascade through trophic levels in feeding webs. That is, predation affects the interactions of many species and influences the species structure of many aquatic communities. Aquaculture escapees can outnumber wild fish. For example, should a medium-sized farm with 100,000 fish lose 3% of the stock, these 3,000 fish might outnumber the wild population of the species, suggesting that competition and predation could become important interactions between the sterile stock, the wild stock, and prey populations. Recognition of these ecological risk pathways has led to greater discussion of aquaculture in on-land, indoor recirculating systems.

Public policy The discussions of food safety and environmental issues posed by transgenic aquatic organisms have raised questions about the adequacy of regulatory oversight3,4,13. Under the Coordinated Framework for the Regulation of Biotechnology, a transgenic fish is regulated by the Food and Drug Administration (FDA) as a "new animal drug" under the Federal Food, Drug, and Cosmetics Act. This approach fosters rigorous regulatory review of a product. Approval for marketing a product can be contingent upon adhering to given methods of production (e.g., use of all-female triploids or recirculating aquaculture systems). Commercialization would be followed by food safety and environmental monitoring, and approval for marketing could be withdrawn if found appropriate. However, the regulatory process is not publicly transparent. The existence and contents of a "new animal drug" application are confidential unless disclosed by the applicant. At the conclusion of regulatory review, FDA would publish its decision and rationale, without having offered opportunity for public comment. The closed nature of the procedure tends to decrease public acceptance of the regulatory process and of the product of biotechnology. Regarding possible environmental impacts of transgenic organisms, the Coordinated Framework invokes the National Environmental Policy Act. However, the act is procedural, requiring only that environmental impacts be formally assessed. Furthermore, FDA has limited environmental expertise.

Other acts might be invoked to apply the authority and expertise of federal agencies to issues posed by transgenic aquatic organisms4,13. These include the Endangered Species Act (lead agencies are the U.S. Fish and Wildlife Service [USFWS] and the National Marine Fisheries Service), the Lacey Act (regarding injurious wildlife species, USFWS), the Non-Indigenous Aquatic Nuisance Species Prevention and Control Act (USFWS), Section 10 of the Rivers and Harbors Act (U.S. Army Corps of Engineers), and the Toxic Substances Control Act (Environmental Protection Agency). However, focusing only on the federal policy framework does not recognize that the states generally have lead authority for management of aquatic and marine resources to the three-mile limit offshore, plus valuable expertise on the species and ecosystems at issue4.

Three recent reviews of public policy covering transgenic aquatic organisms3,4,13 stopped short of recommending that public policies be changed to strengthen regulatory oversight and improve transparency to the public. The Pew Initiative of Food and Biotechnology has a stakeholder forum that may make consensus recommendations14.

Conclusion
AquaBounty, the company seeking regulatory approval for commercialization of GH salmon, also has transgenic lines of rainbow trout and tilapia2. Transgenic lines of GH tilapia and carp are under regulatory review in Cuba and China, respectively4. Scientific and regulatory issues posed by transgenic aquatic species will be debated for years to come.

References

1. Hallerman EM. 2000. ISB News Report, April 2000, http://www.isb.vt.edu/news/2000/news00.Apr.html.

2. Entis E. 2003. Biotech at sea: Innovation required. http://pewagbiotech.org/events/0131/.

3. National Research Council 2002. Animal Biotechnology: Science-Based Concerns. http://www.nap.edu.

4. Pew Initiative on Food and Biotechnology. 2003. Future Fish: Issues in Science and Regulation of Transgenic Fish. http://pewagbiotech.org

5. U.S. Department of Agriculture – Cooperative State Research Service, Biotechnology Risk Assessment Research Program. 2002. Biotechnology risk assessment data: Facts and conclusions. http://www.riskassess.org.

6. Dunham RA et al. 2002. Marine Biotechnology 4:338-344.

7. Aquagene LLC. 2003. http://www.aquagene.com.

8. Winn RN et al. 2000. Proceedings of the National Academy of Sciences USA 93: 12655-12660.

9. Usbekova S et al. 2000. Journal of Molecular Endocrinology 25: 337-350.

10. Lu JK et al. 1996. Proceedings of the National Academy of Sciences U.S.A. 98:3482-3486.

11. Muir WM and Howard RD. 1999. Proceedings of the National Academy of Sciences U.S.A. 96: 13853-13856.

12. Hedrick PW. 2001. Canadian Journal of Fisheries and Aquatic Sciences 58: 841-844.

13. Council on Environmental Quality and Office of Science and Technology Policy. 2001. Case studies of environmental regulation for biotechnology. http://www.ostp.gov/html/012201.html.

14. Michael Rodemeyer, Executive Director, Pew Initiative on Food and Biotechnology, personal communication, January 31, 2003.

Eric Hallerman
Department of Fisheries and Wildlife Sciences
Virginia Polytechnic Institute and State University
ehallerm@vt.edu

source: http://www.isb.vt.edu/news/2003/news03.apr.html 2apr03