Preventing escape of GMO salmon

posted in: Science | 50

It’s been a long time coming. The FDA has finally released their decision about fast-growing, genetically engineered salmon. They state: “After an exhaustive and rigorous scientific review, FDA has arrived at the decision that AquAdvantage salmon is as safe to eat as any non-genetically engineered (GE) Atlantic salmon, and also as nutritious.” It may be safe to eat, but the remaining question is whether wild fish could be at risk from GMO salmon. Back in 2010, I combed through the FDA documents and scientific literature to find out. This post is a summary of the containment measures used for AquAdvantage salmon. See Risk assessment and mitigation of AquAdvantage salmon for the full details.

"Salmoneggskils" by en:User:Kils - en:Image:Salmoneggskils.jpg. Licensed under CC BY-SA 3.0 via Commons.
Atlantic salmon eggs by Hoenny via Wikipedia. AquAdvantage eggs will be prevented from entering the environment by a series of screens and filters.

When Aqua Bounty Technologies, Inc. applied to the FDA for approval of their AquAdvantage salmon, they were very specific about how and where the fish would be raised. The request was for one specific egg production facility in Canada and one specific fish production facility in Panama. The FDA’s approval is for these locations only, and a new approval would be needed for any new locations. Aqua Bounty selected these locations to have many overlapping ways to prevent release of GMO salmon into the environment. Aqua Bounty explains these containment methods in the environmental assessment that they submitted to the FDA. The containment methods are biological, physical, and environmental.

Biological containment

The most important way to prevent AquAdvantage salmon from breeding with wild salmon is to use only fish that can not breed (sterile fish). Most animals in nature have two copies of each chromosome. Fish eggs with three copies of each chromosome (called triploid) can be created by treating fertilized fish eggs with pressure, high temperatures, or certain chemicals. Resulting female fish are not able to produce eggs, so can not reproduce. Triploid fish are used all over the world as a way to prevent farmed or stocked fish from breeding. The pressure treatment used by Aqua Bounty results in at least 98% triploid fish (see page 57). Still, that’s up to 2% of fish that might be fertile, so they must be contained with other measures. To make matters a little more complex, some triploid males can still produce sperm. Aqua Bounty has reduced the risk of fertile fish escaping by using only female fish.

Jumping salmon by Walter Baxter.
Jumping salmon by Walter Baxter. AquAdvantage salmon will not be raised in an environment where they can exhibit this behavior.

Physical containment

Because a small percentage of AquAdvantage salmon could be capable of reproduction, additional containment methods are necessary. At both egg and fish production facilities, multiple layers of security will reduce risk of human sabotage. These include on-facility living quarters for security personnel, security cameras, and 8’ chain link fencing around each property, among other measures. Both facilities use numerous layers of nets, screens, and filters. At the egg production facility, chlorine is used in the drainage area to kill any eggs that escape filters. These containment methods mean less than 1% of fish could escape (see page 55), and keep in mind that 98% of fish are sterile so very few escapees have the potential to lay eggs. Still, it’s possible that the physical containment could fail (such as if a facility wasn’t maintained and all the nets and filters and screens failed) and release additional fish.

Environmental containment

In the highly unlikely case that a fertile AquAdvantage salmon escaped, Aqua Bounty has taken additional steps to further reduce the risk that any escaped fish could breed with sexually compatible male fish nearby.

The egg production facility is located in Prince Edward Island, Canada. The physical containment measures mean very few eggs could make it to nearby bodies of water. Any eggs that did make it past the filters and chlorine would need to find a hospitable place to grow into adult fish. In the past, Atlantic salmon lived in this area, but over fishing, barriers to migration, and acid rain have made them locally extinct so any escaped eggs that managed to grow into adult female fish would not find a male to mate with. In the winter, temperatures in bodies of water near the facility are too low for salmon. Barriers to migration would prevent any escaped fish from moving out to sea during the summer. The eggs are raised in fresh water, and the relatively high salinity in the nearby river would further reduce likelihood of survival.

The fish production facility is located at a high altitude in Panama near a river that drains to the Pacific ocean. Much of the river water (up to 100% in the 4 to 5 month dry season) is used for power generation, and the canals that control water flow to power generation facilities are not suitable for salmon (see page 50). Dams provide a physical barrier to movement downstream. If any fish escaped and they managed to get past the barriers, they could survive in the river closest to the facility. If they try to move out to sea, though, the high temperatures in the lower lower parts of the river would kill salmon (see page 52). While escaped salmon might live in the upper river for a short time, they would not find any males to mate with, and escape to the Pacific ocean is very unlikely.

Worst case scenario

The multiple levels of containment makes it very unlikely that any AquAdvantage salmon could escape into the wild. However, despite all containment efforts, less than 1% of AquAdvantage salmon could escape from the rearing facility and, on average, 2% of the salmon will be diploids. Worst case scenario, that means 0.0002% of all fish reared (2 fish in every 10,000) could be fertile females that escape. These fish then face additional barriers to reproduction and spread of the gene that makes them grow faster than wild fish.

Atlantic salmon reach reproductive age between 1 and 4 years. Farmed salmon tend to reproduce earlier than wild fish, but even if an escaped fertilized egg could hatch, the young fish is unlikely to survive to reproductive age given that the environment near the egg production facility does not sustain salmon. Still, if escape were to happen and the escapee reached reproductive age, what would the result be?

The Atlantic salmon reproductive process requires fresh running water over a gravel bed. Salmon have complex mating and nesting behavior, and a male must be present when the female spawns. In the waters near the egg and fish rearing facilities, there are no males or gravel beds are available. If a female did manage to spawn, the lack of males means the eggs would not be fertilized. In addition, spawning takes so much energy that 60% or more female salmon die after spawning.

Past attempts have failed to reintroduce salmon to rivers near the egg facility and rainbow trout in the rivers near the fish facility. What if those rivers were suddenly able to sustain fish, perhaps due to climate change? Some trout and salmon species can interbreed, but generally produce sterile offspring, so there’s still very low likelihood of risk near the fish rearing facility.  The waters near the egg rearing facility present a little more likelihood of sustaining a sexually compatible salmon male. What would happen if a fertile AquAdvantage female made it to adulthood, was able to spawn, and those eggs were fertilized? More studies are needed on survival rates of fast growing vs wild type and on mixed populations, but research so far indicates low risk of harm.

All AquAvantage salmon carry only one copy of the gene sequence for fast growth, so if an escaped fertile AquAvantage salmon reached reproductive age and found a suitable mate, only one half of her offspring would carry the gene sequence. Those that carried the gene would, according to available research, be at a disadvantage to their siblings that did not.

Fast growing salmon are only able to grow fast if they have an easy food supply. Without extra food, they grow only slightly larger than wild fish. Salmon over expressing growth hormone under wild conditions have decreased swimming speed. Their reduced ability to swim away from predators or catch fish to eat means a higher death rate for fast growing salmon living in a natural environment. Any advantage that fast growing fish might have over wild type fish will likely be cancelled out by negative effects. The gene for fast growth will either be eliminated from the wild population by natural selection or remain at a very low gene frequency, having minimal effect on the population. You may have seen studies that claim a gene for fast growth would spread through a wild population (the so-called Trojan fish theory). From what I’ve seen, those studies assume that the gene does not have negative effects – a very important factor when we’re talking about natural selection.

So even in the worst case scenario where every 2 in 10,000 raised fish escape and are fertile, they will quickly die in the nearby environment, and even if they manage to live to reproductive age they could not find a mate or a place to lay eggs, and even if they did manage to have offspring, those offspring would be at a disadvantage to wild fish, so the AquAdvantage gene would not spread.

Other risks

The FDA has found these salmon to be safe and nutritious. I’ve shown here that there is very little risk to wild salmon populations from AquAdvantage salmon escapes. What about other risks – particularly economic ones?

Additional salmon on the market will affect the wild salmon fishing industry, the farmed salmon industry, and the tax revenues to the states that support those industries. Representatives of the wild salmon fishing industry have expressed concern about escape of farmed salmon, but that concern doesn’t apply to AquAdvantage salmon which are raised in a very controlled environment. Escapes from other fish farms may pose a risk, but that is not a reason to block AquAdvantage. In fact, if AquAdvantage outcompetes other fish farming (such as sea pens) then AquAdvantage might help reduce those other methods – so you can see why the farmed salmon industry might be concerned.

If fearmongering about AquAdvantage salmon continues, people might turn away from farmed fish entirely. This could have a negative effect on the farmed fish industry, and could also have a negative impact on wild fisheries if more wild fish are harvested, and could have a negative impact by removing healthy farmed fish from people’s diets. Of course, these are risks of fearmongering, not risks of AquAdvantage salmon.

Follow Anastasia Bodnar:

Anastasia is Policy Director of Biology Fortified, Inc. and the Co-Executive Editor of the Biofortified Blog. She has a PhD in genetics with a minor in sustainable agriculture from Iowa State University. Her favorite produce is artichokes! Disclaimer: Anastasia's words are her own and views expressed do not necessarily represent the views of her employer. She is not paid to blog or conduct any social media activities. Mention of a company or product does not indicate endorsement.

Latest posts from