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.
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."
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.
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
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.
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
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.