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SUPERFISH: COMING SOON TO A LAKE NEAR YOU?
James S. Thornton
March 07, 1988
Walleye, chinook, bluegill—to anglers, these names conjure up images of fishing trips past. Game fishing in the 1990s may call to mind a more unusual image, like that of a 100-pound chinook that has been injected with cattle growth hormone genes. Spurred by global research in aquaculture, U.S. biologists are manipulating genes and chromosomes in hopes of creating "superfish" for the table and the den wall.
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March 07, 1988

Superfish: Coming Soon To A Lake Near You?

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Walleye, chinook, bluegill—to anglers, these names conjure up images of fishing trips past. Game fishing in the 1990s may call to mind a more unusual image, like that of a 100-pound chinook that has been injected with cattle growth hormone genes. Spurred by global research in aquaculture, U.S. biologists are manipulating genes and chromosomes in hopes of creating "superfish" for the table and the den wall.

"Genetic manipulation is one of the first ideas that come to mind when people want to increase the yield of some source of food," says Anne Kapuscinski, an assistant professor of fisheries at the University of Minnesota. "Some of this research is now spilling over into game-fish enhancement."

Kapuscinski, along with three Minnesota colleagues, molecular geneticists Kevin Guise, Perry Hackett and Anthony Faras, is working under the auspices of the Minnesota Sea Grant College Program to engineer a superwalleye by inserting an extra growth hormone gene into the egg. The researchers hope to produce some of these "transgenic" walleyes by the summer of 1989. They dream of economical "cradle-to-grave" nurseries supplying the nation with walleye, lake trout and other traditionally slow-growing game fish of the upper Midwest. The Minnesota legislature, the project's major funder, hopes the superfish will someday spark a tourist bonanza.

Before that can happen, the products of genetic tinkering must be safe to release into the environment. Says Guise, "We are looking closely at being able to control the growth hormone gene so that we can turn it on while it's in the hatchery and turn it off when it's released into the environment. That way the fish will grow and act like a normal fish in the wild, but the DNR [Department of Natural Resources] will still see an increase in its hatchery efficiency—getting more fish for the buck."

Variations on the "designer fish" concept are already common in sport fisheries. Experimental crossbreeds, from tiger trout (a female brown trout-male brook trout crossbreed) and splake (female lake trout and male brook trout) to the ultra-aggressive result of the cross of a bluegill and a sunfish, are already thriving in the wild. To create the next generation of chimeras, experts in cryo-preservation are trying to freeze fish sperm and eggs so species that spawn in the spring can be crossed with species that spawn in the fall.

Other researchers are focusing on the production of sterilized leviathans. The states of Michigan and Wisconsin, for example, are stocking Lake Michigan with potentially giant chinooks, which have been sterilized either by steroids or triploidy (the inducement of an extra set of chromosomes). Sterilized chinooks never receive the brain signals that tell normal chinooks to spawn and die. As a result, they channel into growth all the energy that otherwise would go into reproduction. While Guise doubts Great Lakes fishermen will ever "go harpooning" for chinooks, those that can elude capture long enough could grow to be huge. Indeed, one computer model at the University of Wisconsin projects a chinook of 100 pounds—four times its normal size.

Of all the brave-new-world fish research going on, none is more fascinating—and disturbing—than gene transfer. Scientists soon hope to splice into a fish's DNA code the ability to resist disease, to grow faster on less food and perhaps even to perform special functions. "There are genes, for instance, that have been isolated from bacteria that will degrade dioxin," says Guise. "It might be possible one day to create a vacuum-cleaner type offish. Take a bottom feeder and put in the right genes...I wouldn't want to eat that fish, but you may be able to engineer biological systems to clean up a damaged environment. We're looking at all sorts of things, but you have to be cautious."

The transgenic research at Minnesota parallels work being done in the People's Republic of China, where aquaculture is a 4,000-year-old tradition. Working with carp and loach, two valuable food species in Asia, Professor Zuo-Yan Zhu of the Institute of Hydrobiology in Wuhan Hubei Province has succeeded in transplanting growth genes that were then passed on naturally to successive generations. While many loach grew 1� times faster than normal loach, some with the extra gene grew two to 4� times faster. The Minnesota team hopes to achieve similar results with walleyes. That effort may get a boost when Zhu travels to Minnesota this spring on a four-month scientific exchange.

From mainland China to the labs of Purina Mills, a U.S.-based subsidiary of British Petroleum, researchers share Guise's exhilaration over ichthyological eugenics. But many of them stress his note of caution—especially when it comes to releasing genetically engineered fish into the wild. "As a scientist with a strong interest in conservation," says Kapuscinski, "I am disturbed that people think we can circumvent nature by just doing fantastic genetic manipulations. We don't really know that much yet about the performance of these kinds of animals in nature, and I think great caution has to be exercised."

Growth-gene implantation is not new to microbiologists, who have been using the technique on laboratory mice for years. With an extra growth gene, mice can grow to about twice their normal size, but no larger. Researchers hope for more dramatic results with fish, many species of which exhibit so-called indeterminate growth that is limited only by food supply, longevity and the amount of energy directed toward reproduction. Some of Zhu's engineered carp, for instance, grow at rates 4� times faster than normal.

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