Those of you familiar with the actual genetics of genetically modified foods would probably laugh in the face of those in opposition to the latest spat with transgenic salmon. What they did was change the promoter sequence for one of the regulated growth hormones for one that is always expressed. In order to do that, they took the growth hormone from Oncorhynchus tshawytscha and used the promoter for an antifreeze gene found in Zoarces americanus and fused the two. This was then integrated into the genomes of Salmo salar to produce breeding stock. After generating a breeding population of homozygous fish, females were then exposed to a hormone which causes the fish to generate male gonads. So you’re left with genetically female but physiologically male fish capable of fertilizing wild-type eggs to produce a homogeneous brood of heterozygous females. Since most people don’t really care about the environmental health, and are only concerned about their own tiny worlds, I have decided to only glance over the ecological dangers (which do exist, and are fairly well dealt, although not to the extent I would like) and focus instead on what health risks such modifications carry.
Growth hormone levels are typically regulated by a myriad of factors ranging from time (time of day, day of year, and years of age) to food intake to environmental cues (such as dietary changes or, as in the case with Salmon, re-exposure to fresh water). The change here is in the sensitivity of the promoter, keeping the “time of day/day of the year” parts of the promoter sequence in the “on” position while diet and food intake still influence total growth hormone levels. The only real change here is that the gene is on for longer, but not in higher levels. This means that consumed genetically modified salmon have no instantaneous higher levels of these hormones than do wild salmon, they just have the highest levels seen in wild salmon more frequently (although, in simulated wild conditions, the fish isn’t much larger; 3-5%). The difference is seen in saturation diets where this fish is fed at maximum rates. These conditions (as would be present in fish farms) produce markedly larger fish (30-50%). This means more food, at lower cost per unit weight, than would be attainable by wild-type salmon.
As for the ecological issues, as previously mentioned, the very slight size difference under wild conditions, in conjunction with >97% sterility, enclosed facilities, and the high predation rate of salmon means the risk of genetic contamination is fairly low (although I still think a synthesis gene for an easily supplemented nutrient of some kind should be employed) for wild stock.
Part 2 of this will examine what foods are genetically modified…