ueled by a $2.5 million U.S. Department of Agriculture grant, Thomas Chen has recently launched a five-year research project to develop fast-growing, disease-resistant broodstocks of rainbow trout using transgenesis technology to support U.S.-based large-scale trout aquaculture.

Transgenesis is the technique of transferring DNA from one species of fish to another. Rainbow trout is an important aquaculture fish species, both for its commercial value as a food fish and for its recreational value to fishermen, notes Chen, director of UConn's Biotechnology Center. Yet large-scale culturing of the species has been limited, because rainbow trout have slow growth rates and are easily infected by bacterial, fungal, parasitic and viral pathogens.

"If by using genetic engineering we can develop rainbow trout resistant to pathogen infection and with faster growth rates, and thus reduce the costs of care, feeding and space requirements, the obstacles that limit profitability of trout aquaculture would be effectively removed," he says.

Chen is widely regarded as a world leader in the field of finfish biotechnology, and a pioneer in transgenesis. He hopes that results from this project can be applied to aquaculture practices with other species, to help meet the growing demand for seafood - a dietary staple for many people and cultures the world over.

Chen says studies conducted in his laboratory have shown that growth and development in rainbow trout and other fish species are regulated by growth hormone and insulin-like growth factors. Introduction of a trout growth hormone gene into common carp, catfish and tilapia (a staple in many parts of the world) by using gene transfer technology resulted in production of fast-growing transgenic fish, with a growth enhancement of between 60 and 600 percent.

"Those results suggest that the growth rate of finfish can be improved by manipulating the growth hormone gene by transgenesis," he says.

Other research has identified in animal species large numbers of low molecular weight peptides that kill microbial pathogens. One group of these peptides - cecropin, originally isolated from a silkworm - is effective in killing bacteria, fungi and other parasites but is not toxic to humans. To learn whether fish capable of producing cecropins would be more resistant to bacterial infections, Chen and his research team produced transgenic medaka fish that could produce cecropins.

"We observed that transgenic medaka expressing cecropin transgenes are resistant to infection by bacterial pathogens," Chen says. "Those results suggest that by applying the technology, we can breed rainbow trout broodfish with elevated levels of resistance to infection by pathogens also."

Chen's new research project will take more than five years to complete. During that time, he aims to:

• Develop prototype genes for gene transfer that will improve growth rates and resist infection by pathogens. To this genetic cocktail, Chen also wants to add a gene that produces high value carotenoids, that would enable rainbow trout producers to control the color of the fish meat through their feeding habits.
  
  
• Introduce the transgenes into rainbow trout sperm by a process known as electroporation. Fry hatched from the sperm will be reared to 10 cm in size and fin tissues will be collected for analysis of the presence of the transgenes.
  
  
• Establish transgenic founder lines by breeding the first transgenic trout with non-transgenic fish.
  
  
• Validate the new transgenic species. Detailed studies will be carried out to assess the performance of each transgenic line introduced into the rainbow trout, both in the laboratory and in aquaculture operation.
  
  

David Bauman