The Daughterless Gene

“The Plot to Kill the Carp” by Todd Woody, in Wired (Oct. 2002), 520 Third St., 3rd Fl., San Francisco, Calif. 94107–1815.

Eight years ago, Australian wildlife officials were alarmed to discover environmentally destructive European carp—which are already dominant in mainland Australia’s waterways—swimming among the rare native fish in Tasmania’s Lake Crescent. Carp, writes Woody, a Sydney-based journalist, are “the Borg of the fish world.” Uprooting aquatic vegetation, they turn clear-running water muddy, depriving native fish of food, light, and oxygen.

Authorities held the rapidly multiplying Lake Crescent invaders in check by lowering the lake’s water levels and denying them space to spawn. But Australian scientists now believe they have a better solution: “daughterless” genes.

“Biologists have long known that female fish develop when an enzyme called aromatase transforms androgen into estrogen,” notes Woody. If aromatase were chemically blocked, fish could be made to produce only males. Biologist Ron Thresher and his colleagues developed a gene to do exactly that. As carp injected with daughterless genes produce single-sex offspring, “the population of each targeted river or lake will eventually drive itself to extinction.”

That’s the idea, at least. The scientists have already proved they can develop a daughterless gene for the zebra fish, a two-inch cousin of the carp. Next comes the destructive, fast-breeding mosquito fish. If that effort is successful, work on the daughterless carp will begin.

Skeptics such as Bob Phelps, director of the Australian Gene Ethics Network, worry about the unknowable consequences of releasing “millions of genetically engineered fish into complex ecological systems.” Woody describes “the nightmare scenario: Daughterless carp somehow escape to other parts of the world and breed with dozens of closely related species. Or they evolve in unforeseen ways into superpests.” Thresher, however, says the daughterless carp would be introduced to a target population only gradually over many years, so there would be plenty of time to halt the process if something went awry.

With the continuing spread of destructive alien species around the world, defensive genetic technologies are also likely to spread, says Woody. Scientists and regulators who are dealing with the influx of alien species in North America’s Great Lakes, for example, are interested in the new technologies as a way of dealing with invaders such as the big head carp, a 50-pound monster from China.