05/23/1991

Transgenic Fish Stocked Into AU Research Ponds

AUBURN, Ala.—Researchers in Auburn University's Alabama Agricultural Experiment Station advanced genetic development of fish one step further today by stocking into research ponds common carp that contain growth hormone genes from rainbow trout. These "transgenic" fish will be evaluated periodically and compared to nontransgenic carp, which share their research ponds.

Release into research ponds built with detailed security measures to prevent escape or removal of the fish was approved by the U.S. Department of Agriculture. Stocking of the transgenic carp represents the next step in developing fish that grow more rapidly due to the inclusion of a single growth hormone-producing gene from another species. The gene donor is a rainbow trout, a fast growing, cold water fish.

"Putting these fish into an aquacultural environment is critical to learning what effect the extra gene will have on various production criteria such as growth rate, body composition and dressout percentage," according to Rex Dunham, an associate professor of fisheries and allied aquacultures at Auburn University. Dunham, who headed the research team that developed the transgenic carp in research supported with Hatch funds through USDA's Cooperative State Research Service, noted that the genetically altered fish grew 20-40 percent faster than nontransgenic carp in aquariums. The Auburn researcher believes the addition of an extra growth hormone-producing gene, in addition to the carp's own growth producing genes, is responsible for the accelerated rate of growth.

Dunham pointed out that testing in an outdoor pond setting is necessary to evaluate many environmental factors that could not be considered in an inside aquarium. Without testing in ponds, researchers could not know whether the more rapid growth of the transgenic carp in the aquarium environment would be the same as in a pond environment.

In inside aquariums, transgenic fish showed little production difference, other than growth rate, from nontransgenic common carp. Such characteristics as survivability, percentage of deformation, color, shape and other measurable production parameters were virtually the same. The transgenic fish only grew faster, which was expected since only a single gene for growth was added to their genetic makeup.

In their new pond home, the transgenic fish will be evaluated monthly and compared to nontransgenic common carp. The Auburn scientists will check such parameters as growth inheritance of the gene, survivability, tolerance to low oxygen levels and susceptibility to disease and predators.

"Putting the transgenic carp into outdoor ponds represents the fourth step in our research project," Dunham said. The first step was to get the gene into the fish, which was done by injecting egg masses with the growth hormone from rainbow trout genes. The second step was to determine if this extra gene was expressed in the genetic makeup of the carp, which was done by growth hormone assays by Dunham's collaborators at the University of Maryland. The third step was to determine if the extra gene was passed along to progeny of the original transgenic carp, which also was done by growth hormone assays, Dunham explained.

If the transgenic carp prove to have the same 20-40 percent rate of growth advantage as shown in inside aquariums and the same lack of other production differences, the first model for developing transgenic fish will be completed. Using this model, scientists conceivably could manipulate the genetic codes of food fish, such as channel catfish. The potential will exist through genetic manipulation for control of diseases and parasites, improved feed efficiency, tolerance of varying oxygen levels and other commercial fish production limitations.

The long term impact of faster growing, not necessarily larger, fish is dramatic. For example, in the United States the cost of importing fish is second only to oil products. So, increased production could help reduce the federal trade deficit. Worldwide the shortage of meat protein is increasing, which could be offset by the ability of fish farmers to produce three crops of transgenic fish in the same time it takes to produce two crops of nontransgenic fish. Not only could fish production be increased, but so could the production of more nutritious fish, because growth hormones tend to promote leaner, higher protein growth.

In the United States, catfish production has increased steadily for the past 25 years. The ability to produce a uniform crop of catfish in less time could help insure the continued growth of this industry. The benefits would be felt by both producers and consumers, because of the increased supply of fish.

"The potential benefits to man are great, but right now, we just want to develop the model by which all these potential changes can be produced. The evaluation in ponds of these carp, which we know possess one extra growth hormone gene, puts us one step closer to having that model," Dunham concluded.

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By:
Roy Roberson