Are GMO Fish Safe for the Environment?

The U.S. Food and Drug Administration (FDA) recently approved the first genetically engineered animal for food consumption, AquAdvantage Salmon, a salmon strain developed 25 years ago by AquaBounty Technologies. The FDA determined that this salmon strain is as safe to eat and as nutritious as other wild-caught or farm-raised Atlantic salmon and they have provided strict guidelines as to where and how these fish can be farmed (authorizing only two specific facilities, one in Canada and one in Panama, to breed and raise them). These fish will likely soon be in our grocery stores and restaurants, despite the resistance of many environmental and food-safety groups as well as skeptical grocery chains and citizens. What exactly are these animals and do they pose a threat to our environment?

Genetically engineered (GE) organisms, also called genetically modified organisms (GMOs), are living plants and animals whose genetic material was artificially altered in a laboratory. Transgenic organisms are a type of GMO in which selected genes of one type of organism are inserted into the genetic makeup of another, distantly related organism. While on the surface this may sound like the work of a mad scientist in a scary science fiction story, the end result may not be that different from plants and animals that have been domesticated and selectively bred to be more adapted to farm environments than to wild environments. In fact, transgenic crops are now commonplace in many parts of the world. However, transgenic animals are not so common... but there are more of them than you are probably aware of.

Today there are more than 35 species of genetically modified fish. Many of these fish species have had their genes altered in such a way that they create an excess of growth hormone, causing them to develop faster and/or grow larger, with the aims of generating more meat in less time with less cost. The growth hormone they are producing is not itself unnatural, but when and how much of this hormone they produce are new to the altered species. The AquAdvantage Salmon is an Atlantic salmon in which researchers added a gene from a Pacific Chinook salmon that regulates growth hormone and a promoter (a DNA sequence that turns on other genes) from an ocean pout that promotes a natural antifreeze protein. This genetic combination results in a higher year-round concentration of growth hormone in the blood of the AquAdvantage Salmon, causing them to reach maturity in two-thirds the time of wild or farmed Atlantic salmon.

The fast growth of these GMO fish concerns environmentalists, but the potential environmental effects of the commercialization of such species are far from clear. On one hand, the reduction in cost of farming these fish may reduce commercial fishing pressures on wild fish populations. The fact that these fish can be harvested sooner could also be good for natural fish populations that are harvested as fish food. But the possibility of escape exists, as farmed fish often escape into nature. How do we best assess and avoid the environmental impacts if GMO fish do escape?

It is difficult to know exactly what the impacts of GMO fish escaping into the environment would be without actually releasing GMO fish into the environment. We can't do that, for obvious reasons, so researchers instead have to rely on inferences based on: 1) experiments on GMO fish in artificial environments (like tanks), 2) experiments on GMO fish in artificial environments that have been made to more closely resemble nature, 3) experiments on non-GMO fish that share many of the same traits as the GMO fish, and 4) computer models that use the data from the previous methods to make predictions about different scenarios. Although not ideal, we can combine information from these various approaches to get a pretty good idea of what might happen if GMO fish were in our natural ecosystems.

The mere presence of GMO fish in an ecosystem is not necessarily harmful, but environmentalists are concerned that these fish may interact with the natural ecosystems in harmful ways. They are primarily concerned about the ability of transgenic fish to compete, persist and reproduce in a natural environment, essentially becoming an invasive species. There are many reasons to think that high levels of growth hormone may influence these abilities, but it is not yet clear how.

The principal effect of high growth hormone levels is an accelerated growth rate. The fact that accelerated growth rates have not naturally evolved in wild fish suggests that they would be disadvantageous in a natural setting. For one thing, fish with excessive growth hormone sometimes have abnormal skull shapes or organ sizes that can reduce their ability to compete and survive in harsh natural conditions. Another critical effect of excess growth hormone is that fish that grow faster also have higher metabolisms and need to eat more. Their high feeding drive means that, if they were to escape, they could potentially outcompete native fish for food. However, their feeding drive is often so high that they spend more time at the water surface, which exposes them to more predators, which may remove them from natural environments sooner. In fact, research suggests that many GMO fish with excess growth hormone only have faster growth rates in highly controlled tanks with lots of food; if food is not abundant and predators are present, some GMO fish actually grow slower than their wild counterparts.

Unlike mammals that mature at specific ages, many fish species mature at specific sizes. A faster growth rate could mean faster maturation and a shorter life span. On one hand, the shorter life span could remove any escaped GMO fish from the ecosystem faster. On the other hand, animals that breed younger have the potential to create more offspring and more generations in a shorter timespan, so the environmental impact over multiple generations could be higher. However, these high growth hormone fish often develop at a rate that is not as matched to the seasonal rhythms as wild fish are. They emerge from their nests earlier than their wild counterparts, which allows them to start feeding on resources sooner, but also exposes them to more predators. In the case of farm-raised salmon, they also have not learned the complicated spawning behavior of wild salmon, which significantly reduces their abilities to successfully find and attract a mate, find an appropriate breeding ground and breed. As an additional precaution, many genetic engineering companies, such as AquaBounty Technologies, have also modified their fish to be reproductively sterile. One of the most common methods of sterilizing these fish is to add an extra chromosome, which prevents the development of functional gametes (sperm and eggs) with a success rate of 98-99.8%.

The general scientific consensus on these fish that have been genetically altered to produce more growth hormone is that they may provide more benefit to the environment than harm, but we don't yet have enough information to be completely confident. We can't ethically study the actual GMO fish in completely natural ecosystems and their traits seem to depend heavily on their specific environmental conditions, so all of our data on these relationships are indirect. However, if the fish are contained in controlled and regulated enclosures, then there is a very small chance of their escape. If they have anatomy that reduces their ability to compete and behaviors that increase their chances of being preyed upon, then in the very small chance that they do escape, they will not likely persist for long. If they are also sterilized and have behaviors that decrease their chances of spawning, then in the miniscule chance that they escape and persist, they will have almost no chance of successfully reproducing and passing on their modified genes in nature. All indications are that these GMO fish are probably safe for the environment. Probably.

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Further reading:

Devlin, R.H., Sunderstrom, F. and Leggatt, R.A. Assessing ecological and evolutionary consequences of growth-accelerated genetically engineered fishes, BioScience, (June 2015). DOI: 10.1093/biosci/biv068.

Image Credits:

Salmo salar-Atlantic Salmon-Atlanterhavsparken Norway (cropped).jpg by Hans-Petter Fjeld at Wikimedia Commons, licensed under the Creative Commons Attribution ShareAlike 3.0 License.

Figure 1 from Devlin et al., 2015 shows examples of GE for high growth hormone production in GE fishes.

Figure 5 from Devlin et al., 2015 shows how the growth hormone transgene can have different effects depending on the environment in which the fish is raised.