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How safe are genetically modified plants in fish feed?

In a new publication, Norwegian researchers have reviewed numerous publications and present the current state of knowledge about the use of genetically modified (GM) plant ingredients in fish feed. The review focuses on fish performance and health, and the fate of DNA fragments from GM plants in the fish

June 1, 2011

How safe are genetically modified plants in fish feed?
In a new publication, Norwegian researchers have reviewed numerous publications and present the current state of knowledge about the use of genetically modified (GM) plant ingredients in fish feed. The review focuses on fish performance and health, and the fate of DNA fragments from GM plants in the fish.

The researchers are from the National Institute of Seafood and Nutrition Research (NIFES), the Aquaculture Protein Centre’s (APC), the Norwegian School of Veterinary Science (NVH), and the National Veterinary Institute (VI). The researchers base much of the review on experiments they have performed themselves.

Why worry?
DNA is present in all cells, so we eat it every day. Is there a reason to worry if we eat DNA from a GM plant?

“When a plant is genetically modified, it is quite random where in the plant’s own genome the new DNA, or transgene, settles. Therefore, some of the host plant’s own genes might be affected and give so-called unintended effects, such as changing the level of nutrients or toxicants in the GM organism”, says scientist Anne Marie Bakke from APC and NVH. “The GM plant as a feed ingredient might therefore have characteristics that we do not know of. It’s also a concern that the new protein itself, produced by the plant from the transgenic DNA, can affect the animal eating it”. These concerns were considered in the review:

Resistance to insects and herbicides
There are two traits that commercially available GM plants are modified for – tolerance to certain herbicides or resistance to insect attacks. Only a few differences were observed between herbicide resistant GM plants and conventional plants of the same species, such as certain soy, cotton and canola plants.

Data on insect resistant plants are scarcer but some relatively pronounced differences between GM-maize and conventional maize have been observed. The researchers recommend that the effect of some insect resistant plants should be followed up, particularly in respect to growth and health parameters of the fish.

In trials reviewed, there was little consistency from trial to trial for a specific GM plant, so drawing any general conclusions on the safety of using GM plants in fish feed is difficult to do. “This may reflect genetic differences between each batch of GM plants, possibly due to random insertion of the transgene into the plant genome, or that there were variations due to differing environmental conditions that each batch of GM plant tested were grown under”, says Bakke.

This is at least how the researchers can account for the variable results observed in the feeding trials with Atlantic salmon done by the APC with NIFES and VI since 2001 in two projects funded by the Research Council of Norway.

“However, we did not see any dramatic effects on fish performance and health”, says Bakke.

What about DNA fragments?
DNA fragments in the diet, whether its transgenic DNA or DNA from a conventional plant, withstand feed processing and intestinal digestion. They can also be absorbed by the intestine and further distributed to tissues in the fish.

However, researchers don’t find any reason to worry about DNA fragments based on what they have studied. Transgenic DNA fragments don’t seem to be taken up more frequently in the intestine compared to the plants’ own DNA, and they don’t seem to cause any negative effects in the fish.

Still, there are several gaps in the knowledge, such as the mechanisms and possible function of dietary DNA uptake, types of cells involved and potential consequences of the uptake.

Distribution
Genetically modified plants were first grown commercially more than 20 years ago. Since then, the proportion of GM crops has increased rapidly. Estimates say that about three quarter of all soy produced globally is genetically modified. It’s becoming increasingly difficult to attain non-GM plant ingredients for fish feed.

The Norwegian scientists recommend more research on the effect of each GM ingredient before using the particular ingredient in fish feed.

The researchers behind the review article are Nini Hedberg Sissener, Monica Sanden and Gro-Ingunn Hemre from NIFES, Åshild Krogdahl and Anne Marie Bakke from APC’s Gut and Health group at NVH, and Lene Elisabeth Johannessen from VI.

Ref: Sissener et al. (2011). Genetically modified plants as fish feed ingredients. Canadian Journal of Fisheries and Aquatic Sciences (Can. J. Fish. Aquat. Sci.) 68, 563-574, doi:10.1139/F10-154.

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