06/18/1991

Dunham Exploring Genetic Options in Catfish

AUBURN, Ala.—Rex Dunham, a fish geneticist working in the Alabama Agricultural Experiment Station at Auburn University, has spent the past 13 years trying to build a better catfish. The result has been a foray into the world of genetic engineering that has yielded success and international attention.

Dunham, who received the CFA Distinguished Service Award recently, earned his B.S. degree in ecology, ethology and evolution from the University of Illinois and his M.S. and Ph.D. degrees in fisheries and allied aquacultures from Auburn. He joined the Auburn faculty in the Department of Fisheries and Allied Aquaculture in 1981 where he has focused on improving the growth and production of food fish, particularly catfish.

"Our overall program is to improve several traits in the catfish," said Dunham, an associate professor in the Department. "These include growth rate, feed conversion efficiency, disease resistance, harvestability, tolerance to low oxygen, decreased fat and changing the body shape to get more meat and less waste."

When he first came to Auburn, Dunham joined a team of scientists that had been working on a crossbred catfish project for many years. By 1988 he had helped produce the "super catfish," a hybrid catfish developed by crossing female channel catfish with male blue catfish.

The "super catfish" grows faster, has higher survival rates, needs less oxygen, has more edible meat and is easier to catch than the traditional catfish varieties used by commercial producers. All these characteristics mean higher profitability for the producer.

But hybridization is not the only area of genetics Dunham has investigated. His work with transgenic fish, fish which have been implanted with genes of other animals, has garnered attention, and some controversy, from throughout the world.

Working with scientists at John Hopkins University, the University of Maryland, and the University of Alabama at Birmingham, Dunham successfully implanted growth hormone genes into both carp and catfish. The genes, from rainbow trout and humans, were implanted by injecting the foreign gene into the one-cell stage of fish embryo using a tiny micro-needle.

Analysis of the fish as they have hatched and matured has shown that the implantation process works. The next step is to determine if the gene can be transferred to the offspring of the host fish. Though other phases of research have been accomplished in the lab, this step requires that the fish be placed in ponds.

When Dunham applied for federal permission to place the transgenic fish in a pond in 1986, a complicated process was set into motion which ended recently with approval for the release.

The carp have already shown signs of more rapid growth in the laboratory and Dunham is hopeful that the process will eventually lead to superior catfish that can reach market size faster, be more disease resistance, and have other beneficial characteristics for production aquaculture. But, Dunham notes, this is only the beginning of a long and complex research program. "We're talking years of research, still," he said.

Dunham was reared on a small farm in Illinois which had a farm pond. His exposure to catfish in this pond, and the publicity that catfish farming was receiving in 1976, led him to Auburn and into catfish genetic research.

"Auburn has a multifaceted approach to improving catfish and uses evaluation, selection, crossbreeding of channel catfish and hybridization between species of catfish, and genetic engineering to improve their commercial qualities," said Dunham. "Likely, the best fish will eventually be produced using a combination of these breeding programs."

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By:
Katie Smith