UM gene-splicers say they see progress in 'redesigning' fish to grow faster, bigger

January 07, 1991|By Luther Young

Just a few blocks from the exotic fish at the National Aquarium, research is under way to "redesign" some of their less glamorous cousins, such as trout and catfish, for faster growth that could revolutionize the farming of fish worldwide.

Through the wonders of genetic engineering, Thomas Chen and his team at the University of Maryland's Center of Marine Biotechnology -- located at the Community College of Baltimore -- have increased the growth rate of certain fish species by as much as 40 percent.

"There's still a lot of work to be done, but this has enormous potential," said Dr. Chen, 48, a molecular biologist and native of Taiwan. "If we can get fish to grow faster, we can significantly increase the world's food supply and boost the aquaculture industry."

Along with a handful of colleagues from China, Japan, Canada and the United States, Dr. Chen has helped pioneer the development of "transgenic" fish, which have been treated as embryos with growth hormone genes from other fish, even from humans or other mammals.

Research worldwide ranges from projects to speed up the growth of fish and impart disease resistance to attempts to transfer into the Atlantic salmon the "antifreeze" gene that keeps the blood of winter flounder from freezing in frigid 28-degree waters.

Still, federal regulatory hurdles remain, and environmentalists' concerns must be addressed about the potential for "super fish" getting loose in lakes, rivers and oceans and wreaking havoc on the balance of nature.

Only one outdoor field test of transgenic fish has been approved in the United States, at Auburn University in Alabama, although at least a dozen fish species have been successfully altered in American laboratories. The fish were released into a pond isolated from other populations and from which they could not escape.

"This is the ongoing dilemma of genetic engineering, where the technology has gotten way out ahead of the regulatory framework," said biologist Eric Hallerman of Virginia Polytechnic Institute and State University. "We need to take the proper precautions."

Scientists learned in the 1970s to manipulate genes, the complex DNA molecules that dictate every characteristic of living organisms. They have "spliced" genes from other species into hundreds of microbes, plants and mammals, including cows, pigs and mice, seeking to improve on nature.

But it wasn't until the mid-1980s they looked at fish.

Research had proven that mammalian growth hormone genes injected into cell nuclei of developing embryos and returned to the female's uterus often resulted in animals that outgrew and outweighed their normal siblings.

Chinese researcher Zuoyan Zhu -- now working at COMB with Dr. Chen -- performed the first successful gene transfer in fish in 1984 by inserting a human growth hormone gene into fertilized goldfish eggs, then incubated naturally in water. Since fish embryos don't have to be returned to the womb, the process was far easier than gene transfer in mammals.

"Some people react strangely about human growth hormone in fish," said Dr. Chen, who added that some of Dr. Zhu's goldfish did grow two times larger than normal. "But that doesn't mean fish get human, or cow, or rat characteristics. It just doesn't work that way."

In 1986, Dr. Chen joined the newly formed COMB -- one of six research components of the Maryland Biotechnology Institute -- and joined forces with Dennis Powers, then at the Johns Hopkins University, and Rex Dunham of Auburn, to produce a breakthrough in transgenic fish research.

They isolated and cloned, or synthetically reproduced, a growth hormone gene from the pituitary gland of rainbow trout and injected it into carp embryos, producing in about one of 10 cases a carp with enhanced growth. The technique also has worked with catfish.

Some of those fish have successfully passed along the characteristic to their offspring, holding out hope for raising a breeding colony of the fast-growing fish.

The mechanism is not fully understood, but Dr. Chen points out that in normal animals, only the pituitary gland makes the growth hormone. When the fish embryo is injected with the foreign gene, its natural growth system is overridden and more hormone is produced.

It's a tedious process, and one tantalizing outgrowth of the research is that a rainbow trout injected under the skin or dipped with its own growth hormone -- not the gene, but the actual growth protein produced in the pituitary -- absorbs some of the material and grows faster and larger.

But that method requires a lot of hormone, and the amount used is extremely critical. Too much or too little can result in lessened growth or even death.

"We feel it's most economical at this point to let the fish make the growth hormone," Dr. Chen said. "We've only isolated the gene for rainbow trout so far, and we're still working on that for other fish species."

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