By John McQuaid, "How to Make a Salmon,"March/April 2011
To make the AquAdvantage transgenic salmon, scientists select two sequences of DNA—one from a Pacific chinook salmon, the other from an eel-like fish called the ocean pout, which has antifreeze proteins in its blood that help it live in near-freezing waters. The genes are chemically knit together and injected into fertilized Atlantic salmon eggs, some of which incorporate them into their genetic makeup. But that’s only the beginning: in additional steps, eggs from those transgenic fish are isolated and biochemically “tricked” into developing without fertilization, a procedure known as “gynogenesis.” The resulting all-female fish—still carrying the new genes—are then treated with a hormone that turns them into males, and their sperm is used to fertilize ordinary salmon eggs. It’s these offspring that are intended for the dinner plate.
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In an elegant feat of genetic engineering, the foreign DNA strands reprogram the salmon’s metabolism: the chinook gene signals the manufacture of extra growth hormones, while the ocean pout gene (which normally signals the production of antifreeze proteins when the temperature drops) keeps that internal hormone factory switched to “on” during the winter months, when ordinary salmon stop growing. As the embryos mature, the foreign genes accelerate their growth: a tiny fry grows to a 13-pound adult in two years—twice as fast as an ordinary farm-raised fish. Thus the fish can be farmed year-round, in any climate, and more production cycles squeezed into less time.