by Alexandra Simas
Fish are a fabulous source of many nutrients, including omega-3 fatty acids. Growing popular demand has strained the limits of commercial fishing. Farmed fish help meet the growing need, but this system still has a significant environmental impact. Working towards the goal of increasing aquaculture efficiency, Massachusetts-based AquaBounty has created the AquaAdvantage® salmon, the first genetically-modified (GM) animal approved by the FDA for sale and consumption.
What makes AquaAdvantage® salmon different?
These GM salmon grow rapidly and reach consumption size far faster than their non-GM Atlantic salmon counterparts. This increased growth is a result of inserting a modified Chinook salmon growth hormone gene, which produces a protein very similar to the Atlantic salmon’s orthologous protein, into the Atlantic salmon.
The key difference lies in the promotor, which controls timing and quantity of growth hormone production. The endogenous salmon promotor regulates growth in a seasonal manner i.e. the salmon grow more when the environment is conducive to growth. Conversely, the Chinook gene is inserted along with a promoter from an eel, the ocean pout. In the pout this promoter regulates the production of an antifreeze protein. Since this protein prevents the eel from freezing in its sub-zero natural habitat, it’s important to produce it at constant levels every day of the year. AquaBounty takes advantage of this perpetual green light to ensure their GM salmon are pumped full of growth hormone every day of the year.
The increased growth means AquaAdvantage® salmon are full-grown within 18 months rather than 2 years for conventional farmed salmon or 3 for wild, allowing greater food production and/or reducing environmental impact.
Next step, take over the world?
A common concern with genetically modified organisms is their interaction with the environment and native species. AquaBounty is confident its precautions will prevent their salmon from escaping to natural salmon habitats, by growing salmon in tanks on land (though this does not mean the tanks can’t be near rivers or lakes). In the case that their salmon do reach the ocean, all salmon raised will be both female and sterile.
The sterility is achieved by making the fish triploid. This means they possess two copies of each maternal chromosome and one copy of each paternal, for a total of three copies of each. Fish, like humans, are naturally diploid, possessing only one copy of each chromosome from each parent. Triploid animals do occur rarely in nature, but are usually sterile. Producing female, triploid fish populations via temperature shocks, high pressures, or chemical treatments is already an established practice (with 99% accuracy), employed by companies such as Troutlodge to supply “trophy trout” for sport fishing with minimal impact on native populations. A key point here is that a small population of diploid i.e. fertile salmon must always be raised to breed the next generation.
One concern about GM organisms is that they may be more fit than their conventional counterparts, giving them an unfair advantage if they escape containment. In a review published earlier this year, Robert H. Devlin, a research scientist with Fisheries and Oceans Canada, headed a team that sought to elucidate the potential environmental impact of escaped GM salmon. They did this by reviewing over eighty studies on fish genetically modified through the addition of growth hormone transgenes. They concluded that GM fish are usually created from strains closely related to their wild counterparts, and therefore are quite capable of interbreeding should fertile fish escape. However, the differences between GM and wild fish do not necessarily confer advantage. The increased growth comes at the cost of other functions, such as immune function and swimming ability.
On the other hand, Fredrik Sundström, an ecologist at Uppsala University in Sweden and another author on this study, contends that “it’s very difficult to predict any ecological consequences before these fish are actually in nature, when it’s kind of too late to do anything about it.” Will they dominate due to their size, or will their phenotypic tradeoffs ensure they die off without having much impact on the native ecosystem?
Like all livestock, farmed fish are more prone to disease and infection because of their close living quarters. Any farmed fish escapees spread pathogens among the wild population. If GM salmon escape and outcompete wild-type salmon due to their large size, they could spread the pathogens more widely. Furthermore, even if the escapees are sterile, the competition could effectively reduce the wild population by starving out the wild salmon.
Are GM salmon more likely to cause allergies?
Fish is a common allergenic food, and genetic modification can affect protein production. Could AquaAdvantage® salmon be more allergenic than other salmon? The FDA found that AquaAdvantage® triploid allergenicity was no different from non-GM, wild caught salmon. However, caveats include a sample size of just six fish per group, and that only wild caught salmon were used as controls, in contrast to many of the other tests performed, such as fatty acid profile, where farmed salmon were included. Since these salmon are farmed, farmed salmon are a better control. Returning to the breeding diploid population mentioned above, GM diploid salmon possessed higher allergenic potency in one test, while other tests performed were flawed and could not be used according to the FDA. They concluded that “insufficient data and information were available from which to draw a conclusion regarding possible additional allergenic risk posed by diploid [GM] salmon.”
How do I know if I’m eating GM salmon?
You wouldn’t unless the vendor volunteers that information, since there are no laws requiring labelling of GM foods. But what vendor is going to choose to tell you?
No matter how thorough testing of new products is, innovation is always accompanied by a certain amount of risk in the unknown. History is filled with novel policies or inventions, like DDT and Agent Orange, chlorofluorocarbons, or BPA, that seemed wonderful at the time, and based on the cutting edge scientific research of that day they were deemed safe. But as new scientific knowledge was discovered they were found to be extremely harmful. The thing is, we can only test and look for markers or effects we already know exist. Additionally, as time passes studies with longer time points can be performed by independent bodies.
Genetically modified products may prove to be completely harmless in the long run, but we don’t know what the future will hold. The FDA has determined that since the GM salmon are not materially different from their conventional counterparts (they may be bigger, but they have the same nutrient profile) they don’t require labelling. But what if tomorrow a researcher discovers a new marker that is biologically relevant to those consuming it and is substantially different between GM and conventional?
In the meantime, many groups are demanding mandatory labeling. Mandatory labelling would not prevent the sale or purchase of the GM products. While some consumers without strong opinions might gravitate towards a non-GM product if offered a choice between the two, thus reducing sales of GM products, the fact that a company would sell more product if they didn’t have to give consumers more information about it hardly seems a compelling reason to not require labelling. Mandatory labelling wouldn’t harm any consumers, and it would only help consumers make better decisions.
The bottom line:
Genetic modification has incredible potential to improve our lives, diets, and environment. However, we still have much to learn about the biological effects of both genetic modification and traditional breeding, and a lack of evidence against something is not necessarily equivalent to evidence in favor of something. In the case of AquaAdvantage® salmon, my primary desire is, as usual, to see more independent studies with longer-term outcomes (and sample sizes greater than six!). Beyond that, my major concerns at this point are more about the effects of farming on things like nutrient profile and pollutant levels than about their genetic modification, though due to their reduced immune function, I would be even more concerned about the rates of antibiotic usage on GM salmon than conventionally farmed salmon.
Alexandra Simas is a second-year PhD student in Biochemical and Molecular Nutrition.