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Saturday, November 21, 2009 |
- MYTH 1: Transgenic salmon grow much larger than other salmon - so much so that they could gain a mating advantage or outcompete native salmon for food or space.
- FACT: Transgenic salmon grow faster than other salmon but they do not grow any larger by the time they reach maturity.
- FACT: Male salmon do not gain a mating advantage because of size. In fact, "precocious parr," only 6 inches in length, father about one-fifth of each new generation before they go to sea. Studies of escaped farmed salmon, which are almost always larger than wild fish, have found them to mate successfully only 3 percent as often as native salmon.
- FACT: Farmed salmon are trained to eat fish feed -- small, dry pellets that look exactly like the "dog chow" we feed our family pets. If they escape, they look for something similar. Most don't find it. More than 85 percent of the farm escapees caught off British Columbia and Alaska had no food in their bellies. In a 1999 study, the Washington State Department of Ecology found farm escapees to be eating tree bark in local rivers, because it apparently looked like fish feed. Transgenic salmon may forage even more poorly because they lack the critical swimming speed to pursue prey, deplete their energy reserves more quickly and expose themselves to predators more often in the search for food.
- MYTH 2: If transgenic salmon do breed successfully with native fish, their novel gene will escape into the wild gene pool and destroy native salmon populations. Researchers at Purdue University found that only 60 transgenic salmon could drive a wild population to extinction.
- FACT: The U.S. Food and Drug Administration will not approve the use of
transgenic salmon unless they can be demonstrated to be sterile. Aqua Bounty
Farms has stipulated that it will market only sterile, all female transgenic salmon.
There can be no gene flow to wild salmon because sterile fish cannot reproduce.
- FACT: Muir and Howard, the Purdue scientists who proposed the "Trojan Gene
Hypothesis," did not study transgenic salmon. They designed a mathematical model based on the behavior of Japanese medaka, a small, freshwater fish that matures in 56 days and breeds daily until it dies. Salmon take three, five and even ten years to mature and most breed only once in their lifetimes. Sterile salmon do not breed at all.
- MYTH 3: Sterilization is not 100 percent effective so we can't be sure that transgenic salmon will really be sterile.
- FACT: Triploidy produces complete, 100 percent sterilization in female salmon
because it prevents the development of the ovaries needed to produce eggs. The only uncertainties about the technique have been raised in the context of male salmon, grass carp and oysters. There is no scientific debate over the complete sterility of triploid female salmon.
- FACT: Scientists can test for triploidy by scanning blood or embryonic fluids in a flow cytometer. The sterility of every batch of transgenic salmon eggs can be verified before they ever leave the hatchery.
- MYTH 4: Transgenic salmon are voracious predators that will consume all the available food in an ecosystem and will prey on native juveniles.
- FACT: Transgenic salmon actually consume less food per pound of weight gained because they process their food 10 to 30 percent more efficiently.
- FACT: Transgenic salmon may be highly prone to starvation in the natural environment as they learn to identify and hunt for wild food. They maintain a higher metabolic level for a longer period of time in food deprivation studies, and deplete their energy reserves more quickly than do standard salmon.
- FACT: Any food competition would occur in the marine environment because sterile transgenic salmon cannot produce the juveniles that occupy freshwater habitat. In the marine life stages, transgenic salmon would compete with older native salmon of about the same size. Because food availability is not limiting in the marine environment, transgenic salmon would gain no advantage from their higher feeding motivation.
- FACT: Sterile female salmon do not engage in spawning behaviors and almost never return to freshwater habitat after they begin to feed at sea. Native juveniles are confined to freshwater habitat. Any predation risk would, therefore, be lower than now occurs in conventional salmon aquaculture. There is no evidence of predation by current farm escapees on native juveniles.
- MYTH 5: Transgenic salmon produce antifreeze proteins and excessive amounts of growth hormone.
- FACT: Transgenic salmon produce no antifreeze proteins. Only the molecular "switch" from the antifreeze gene is used.
- FACT: Transgenic salmon produce the same amount and kind of circulating growth hormone as wild-type salmon, but they produce it through the entire year.
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