Sorting Out The Myth And Reality Of Transgenic Fish

salmon fillets i i

hide captionIt may look like a salmon and taste like a salmon, but consumers aren't so sure about genetically engineered salmon.

AquaBounty Technologies
salmon fillets

It may look like a salmon and taste like a salmon, but consumers aren't so sure about genetically engineered salmon.

AquaBounty Technologies

It was only hours after I’d become intrigued by Marcelo’s blog on genetically modified salmon, and had started reading up on them to write a follow-up blog, that I became aware of two earlier NPR postings on the topic here and here. So I’ve by now also taken in hundreds of comments from the NPR community in response to this technology, most highly negative.

Is there anything left to say? I think so.

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hide captionWenonah Hauter of Food and Water Watch, carries a box containing public comments opposing the Food and Drug Administration (FDA) approval of genetically engineered salmon she is submitting to the committee before she spoke at an FDA veterinary medicine advisory committee hearing on modified salmon in Rockville, Md., Monday, Sept. 20, 2010.

Associated Press
3_Modified_Salmon.sff.jpg

Wenonah Hauter of Food and Water Watch, carries a box containing public comments opposing the Food and Drug Administration (FDA) approval of genetically engineered salmon she is submitting to the committee before she spoke at an FDA veterinary medicine advisory committee hearing on modified salmon in Rockville, Md., Monday, Sept. 20, 2010.

Associated Press

First, I was reminded yet again that many persons are pretty uninformed about basic features of the natural world, which is to the shame of our educational systems. One commenter, for example, expressed concern about what ingesting modified genes will do to humans and human children, apparently unaware that there’s DNA in all our foodstuffs and it’s fully digested in the gut. That some NPR commenters are as yet unfamiliar with such core understandings is an indication of the educational challenge before us.

I was also reminded yet again of the confusion in the minds of many between technology – which this clearly is – and the science behind it, enabling the expression of deep anti-science sentiments (a phenomenon I’ve analyzed here and here).

But my focus this afternoon will be on the fact that when I started trying to find out what, exactly, had been done to generate this fish in the first place, the project proved to be pretty daunting, and once I was finally able to track down some information, it became clear that the fleeting bits of information presented in the “mainstream media” were often inaccurate if not flat-out wrong. Hence hundreds of commenters were angry about something that they were unlikely to have understood even if they’d been inclined to do so.  A lone informed voice in this wilderness was P L (pembi), who lifted up many facts that I was able to confirm. But his comments were usually ignored in the uproar.

So here’s what I came to learn in reading peer-reviewed research articles on the topic where, given that this isn’t my field, I’ll welcome corrections.

A gene encoding the fish growth hormone (GH) protein was isolated from the genome of the Pacific salmon and introduced into the genome of the closely related Atlantic salmon. The two genes are virtually identical  — the Pacific gene was used only because this allowed scientists to distinguish its expression from expression of the endogenous Atlantic gene. The fish GH has no influence on the growth of humans; indeed non-primate mammalian GH’s are not recognized as growth-stimulating by human GH receptors, let alone fish GH.

All genes are provisioned with “switching elements,” aka promoters, that govern in which tissues, and under what conditions, the gene is expressed — for example, your hemoglobin-encoding genes are provisioned with promoters that restrict expression of hemoglobin to the precursors of your red blood cells. The native GH promoter in fish restricts expression of GH to those seasons when the fish are feeding; hence the fish fail to grow during cold seasons. This is obviously a smart adaptation for fish living in the wild, but when they are farmed, the fact that they are being fed but not growing is a waste of resources.

So, the Pacific gene was modified: its native promoter was excised and replaced by a promoter, derived from the ocean pout fish, that normally regulates expression of what’s called anti-freeze protein (AFP) that protects the pout fish from cold temperatures.  Importantly, the AFP gene itself was not introduced — just the promoter — a feature garbled in several accounts. Since the AFP promoter drives gene expression in cold seasons, the modified salmon produce transgenic GH in cold seasons, and hence grow all year long, meaning that they reach market size (4-6 kg) in 18 months rather than the typical 36. It’s not like they get huge — they’re not hyped-up Barry-Bonds/Mark McGwire equivalents, where the image accompanying Marcelo’s and others’ blogs can give that erroneous impression.

A recent study1 makes a particularly interesting point. When an engineered GH-transgene was introduced into wild-caught salmon, growth rates were enhanced as expected, but when it was introduced into a domesticated salmon, bred since the mid-1980s (~ 12 generations) in a commercial fish farm selecting for rapid growth, there was little enhancement. Moreover, when the transgenic wild fish and the domesticated fish were compared, their physiological parameters were similarly to one another.

In other words, the standard human practice of domestication – breeding wild organisms and selecting desired traits – that has been ongoing for thousands of years has, in this case, generated much the same outcome as the modern practice of transgenics: both act to modify similar genetic pathways. Indeed, the authors note that most domesticated species selected for size, like beef cattle, are quite unresponsive to mammalian GH-transgenes. Genetically, they’re already as bulky as they’re going to get.

So – if one is “against GMO’s,” then one should, to be consistent, be “against domesticated animals and plants” as well, restricting food intake to wild organisms (some grasses are still OK, but no wheat or rye; no chicken eggs; etc.). While fish are currently among the few animal-based foods still extant in the wild, they are being rapidly driven to extinction by overfishing  — if present trends continue, most fisheries are predicted to be depleted by 2050 — so this position raises important ecomoral issues.

And then, there’s a larger point. Evolution occurs as the result of natural selection for adaptive traits. In some cases the selective agents are non-living (wind, cold, fire, meteors, etc.) and in the remaining cases they are. Birds select for the camouflage of moths; plants and birds fine-tune the shapes of flowers and beaks; lions select for speedy zebras. We living humans are the same, albeit we use these things called minds that work at very different time scales from most evolutionary agents. As Marcelo put it in a comment: “We can’t neglect the fact that we humans are a changing force in our world. May it be used wisely as opposed to blindly.” To my mind, the transgenic salmon is a wise, indeed elegant, contribution to our blind pillaging of our waters.

1Delvin et al, Proc. Natl. Acad. Sci. 106: 3047, 2009

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