Would you believe a transgenic Pacific salmon that was 37 timesheavier than its native sibling fish?When molecular ichthyologist Robert Devlin and his team at theCanadian Department of Fisheries and Oceans inserted hyperactivepiscine growth-hormone genes into the fertilized eggs of coho salmon(Oncorhynchus kisutch), their purpose was "growth enhancement as astrategy to shorten long production cycles, and improving feed-conversion efficiencies," not "producing whale-sized salmon." Fish,unlike mammals, continue to put on weight and size throughout theirentire lifetime.A one-page communication titled "Extraordinary salmon growth," inthe current Nature (Sept. 15), describes how Devlin et al. "developed agene construct where all genetic elements were derived from sockeyesalmon" (Oncorhynchus nerka). This all-salmon expression vector wasmotivated by "public concern over the use of DNA from non-homologous sources."Indeed, when a local Vancouver newspaper last Friday asked 67 of itsreaders, "Would you eat genetically engineered salmon?" only 30percent said they would; 70 percent answered "No way." One typicalresponse: "No. I wouldn't eat that kind of salmon. It kind of scares meto think what people will be doing next."This is why research associate and lab factotum Timothy Yesaki toldBioWorld Today, "Our lab is strictly research. We don't see such fish-farm transgenic salmon becoming available on the market before 20 or30 years. Because of public opinion, this is going to take getting usedto. So we've got a ways to go yet."Transgenic Frequency In Mouse BallparkMeanwhile, no one has sampled the meat of the transgenics. "Thesefish are worth quite a bit of money," Devlin told the newspaper, "so wedon't want to chop them up and throw them on the barbecue quite yet."At their research laboratory in West Vancouver, B.C., the teammicroinjected their linear DNA construct into more than 3,000 eggs.After one year, they found that 6.2 percent of surviving fish retainedthe gene in their fin tissue. This frequency compares with 5 percentobserved in transgenic mice, Devlin told the 5th World Congress onGenetics Applied to Livestock Production, last August in Guelph,Ontario.About 20 to 30 of the parental-generation, genetically engineeredsalmon parr (yearlings) are alive and well in the lab's aquarium. Onaverage, they are 11-fold heavier than controls. The 37-fold specimen,now 14 months old, weighs about 428 grams at one year, Yesaki said."Hopefully," he added, these founder transgenic fish "will be maturingthis fall or next spring. We will then try to produce second-generationoffspring, and cross them with normal salmon, hoping the gene willpass to the second generation." He added, "Our transgenic fish willmature after two years; normal fish in about four."Devlin told the Guelph meeting that "In one of our studies, fivetransgenic male coho salmon sexually matured precociously at twoyears of age, rather than the normal three years for this species."Salmon parr, he explained, undergo a process called smoltification,during which they clothe themselves in silvery scales, in preparationfor migrating in the spring from fresh water to the salt sea. "They hatchout of the rivers and make their way down to salt water, which is a bigsink of proteins for them to feed off of. There the smolts feed on otherfish and protein. They can really grow in the salt water."Maximum Escape-Proof ContainmentGrowth hormone levels, normally very low in fresh water, rise in thespringtime along with the smolts' departure for the marineenvironment.Tall tales of "the one that got away" are not likely in the group'sresearch environment. "We are under strict rules and guidelines toprevent our transgenic fish from escaping," Yesaki said. "Inside ourbuilding we have an indoor aquarium, in which our fish are housed.Inside the aquarium there's floor-to-ceiling chain-link fencing, infraredbeams, motion detectors and triple-screen traps to prevent them frombeing killed or stolen, or escaping to the wild."Co-author Penny Swanson of the U.S. National Marine FisheriesService in Seattle, analyzed levels of growth hormone from plasmasamples. Woon-Khlong Chan of Singapore's National University cameto Vancouver to take part in constructing the growth-hormone cloningvehicle.This expression vector, the Nature paper noted, "consists of themetallothionein-B promoter fused to a full-length growth-hormonegene." Its concept, it said, is identical to the construct first used todouble the size of mice.Lab director Devlin was not available this week to speak withBioWorld Today. "He's off fishing in the interior of the province,"Yesaki reported; "He's gone after rainbow trout." n
-- David N. Leff Science Editor
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