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Risks involved with transgenic fish

Date: 17.9.2009 

Fast growing transgenic fish can revolutionise commercial fish farming and relieve the pressure on overexploited fish stocks. But what happens in the natural environment if transgenic fish escape? Researchers at the University of Gothenburg have studied transgenic fish on behalf of the EU and are urging caution:

"Until further notice transgenic fish should be bred in closed systems on land," says Fredrik Sundström at the Department of Zoology, University of Gothenburg, Sweden.
By furnishing fish with genes from other organisms, so-called transgenes, researchers have succeeded in producing fish that grow considerably faster or are more resistant to diseases. Fish can also be modified to cope better with cold, which facilitates breeding in colder conditions.

Genetic modification

Genetic engineering processes are becoming increasingly common and are being applied to a widening variety of organisms. Genetic modification involves identifying genes scientists hope will express the desired traits when introduced into fish. These new genes can come from other species of animals, plants, bacterium, and even humans.

There are several processes used to insert "new" DNA into fish, ranging from inserting genetic material directly into eggs to subjecting fish eggs to electrical pulses, which form pores and allow foreign DNA to access the eggs. The precise location where the new genetic material has attached to the original DNA is unknown and may vary between individual fish so scientists need to check to ensure the inserted gene is present and determine if it functions as expected. Once scientists have determined that the genes have been inserted, the fish are raised like other farmed fish.
Although this article is focused on transgenic fish, other transgenic aquatic organisms, including marine and freshwater plants and shellfish, are being fast-tracked for commercialization.

Food Safety Issues

There are major benefits for commercial fish farming as transgenic fish are expected to deliver higher production and better yields. However, transgenic fish can also entail risks and undesirable effects on the natural environment.

For example, genes inserted to promote disease resistance may cause transgenic fish to absorb toxic substances (like mercury) at a higher rate and pass these toxic substances on to consumers.
The majority of transgenic fish have been inserted with growth genes. There are also misgivings that the large doses of growth hormones may pose health risks if consumed in raw and uncooked foods like sushi.

Roughly 90 percent of food allergies can be attributed to consumption of eggs, fish, shellfish, milk, peanuts, soybeans, tree nuts, and wheat. If proteins used in the production of transgenic species originate from one of these eight sources, there may be potential for allergic reactions among consumers.

Researchers at the University of Gothenburg have therefore been commissioned by the EU to study the environmental effects of genetically modified organisms (GMO) within fish farming. The results of the studies show that the genetically modified fish should be treated with great care.

Simulated escapes

Millions of farmed fish escape from open water facilities each year and contaminate native populations and it is inevitable that transgenic fish will escape from aquaculture pens or field trial parameters. Therefore Sundström has studied transgenic salmon and rainbow trout to ascertain what ecological risks they might constitute for the natural environment. The study, which simulated escapes in a laboratory environment, shows that transgenic fish have a considerably greater effect on the natural environment than hatchery-reared non-transgenic fish when they escape. Genetic alterations in transgenic fish may give them competitive advantages over native species.

For example, genetically modified fish survive better when there is a shortage of food, and benefit more than non-transgenic fish from increasing water temperatures. By using growth hormone genes, researchers have been able to increase growth rates 2 to 11 times faster than the normal rate. Faster development leads to earlier sexual maturity and potentially more breeding opportunities than their native counterparts.

Natural breeds are under threat

If transgenic fish are genetically enabled to breed earlier and at a faster rate, transgenic genes are more likely to be spread throughout native populations. This would reduce the genetic diversity of the native population. Transgenic fish may have similar effects on natural ecosystems as exotic species. An increased growth rate is often accompanied by a voracious appetite, and transgenic fish may out-compete native species for resources, destroy plants and sensitive habitat, and/or alter the food chain in an ecosystem.

However, conducting studies in a laboratory environment that imitates nature is complicated, which makes it difficult to predict how escaped transgenic fish affect the natural environment. Sundström's conclusion is that international consensus is required before commercial farming can be permitted, and that a precautionary principle must be applied.

"One option is to farm the transgenic fish on land, which would make escape impossible. At least fertile fish should be kept in a closed system," says Sundström.

As of yet no country has permitted commercial farming of transgenic fish, but several applications for such operations are under consideration by authorities in both the USA and the EU. Neither other genetically engineered food animals have been approved for sale, although numerous animal species have been cloned (but not sold for food) and transgenic animals are producing commercial, nonfood items such as spider silk (by goats).

Picture: At 18 months, the transgenic Atlantic salmon (Salmo salar)is clearly much larger than the same-age normal fish. But overall growth of the same generation of fish evens out by 36 months

Author: Dagmar Smětalo






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