A Visit to the National Center for Cool and Cold Water Aquaculture

by Claire Stuart

With all of the emphasis on healthy eating in recent years, fish has become an important part of the diets of millions of people. Research that will help to bring healthy, productive fish to the table is going on right here in Jefferson County at the National Center for Cool and Cold Water Aquaculture (CCWA) in Leetown.

CCWA is part of the U.S. Department of Agriculture’s Agricultural Research Service. “We are a recent addition to USDA,” said Rexroad of the lab that opened in 2001 across the road from U.S. Geological Survey’s Fish Health Laboratory. “We share the same water supply,” said Rexroad—about 500 gallons of water enter the facility every minute. “The place runs on more like 1,500 gallons per minute,” said Rexroad, but because water is re-used for multiple purposes the intake is only a third of that.

“What we do here is research and technology transfer,” said Center Director and Research Leader Dr. Caird Rexroad III.

CCWA’s work involves fish health, physiology and genetics, and genomics. In genomics, organisms are studied in terms of their genomes—the total of all of their genes as they work together. The center operates with a staff of 10 scientists, 15 technicians, and 10 facility and clerical support people (including a crew of seven working in the “wet labs”), along with occasional post-doctoral researchers.

Rexroad was the first bench scientist hired at the lab, and he became director in April 2008. His family was originally from the small central West Virginia town of Lumberport, but he grew up in Laurel, Maryland, where his father was a researcher at the huge Agriculture Research Facility in Beltsville. “I’m second generation in the USDA-ARS,” he said.

The center’s research includes selective breeding of rainbow trout for disease resistance, growth and stress tolerance. They have sequenced the DNA of rainbow trout, and are working to create a genetic map for important traits and understanding the biochemical processes of how fish grow. They have also sequenced the genomes of bacterial pathogens and lowered incidence of fish diseases by selecting resistant fish.

Anyone entering the “wet labs” where fish are raised must don sterile boots and walk through disinfectant to prevent introduction of any organisms that could affect the fish. In the labs, fish are raised in huge tanks and fed by a computer-controlled, robotic feeding system. The system weighs the total biomass of fish in the tank and feeds a certain percent of body weight daily. Young fish are fed by hand. Water is filtered and recirculated, and pipes to the tanks can heat, chill or add oxygen to the water.

Fish are implanted with electronic tags similar to the identification tags implanted into pets. The tags can be read by a computer, so that researchers can get the facts about any individual fish over time. Experimental conditions mimic production stresses such as temperature fluctuation, salinity, crowding and handling, to examine fish response.

In one fish room, large numbers of female trout are held for two years to study reproductive physiology. Information about how certain hormones react to certain stimuli will help to control reproduction so that there will be a good balance of growth with reproductive efficiency. The goal is to get good eggs to grow into healthy fish.

The genetics room houses large numbers of fish families from cross-breeding experiments. Over 300 crosses are done each year. Fish from each cross are kept separate until they are big enough to be tagged.

Interestingly, the fish used are all-female lines because females grow more consistently than males. A number of fish from each cross are fed hormones to masculinize them. This results in fish that are genetically female but physiologically male. This is not a new process; it has been used in fish breeding for many years.

Milt (sperm-containing fluid) is harvested from the “male” fish and frozen until it can be matched with eggs from “real female” fish because eggs can’t be frozen.

Rexroad emphasized that hormones are eliminated from the water before it leaves the facility. All the water they use is strictly managed and monitored. It is filtered and treated with UV, going to a settling pond before it is returned to the environment. “It goes back to the stream as good as the ground water we started with,” he said.

In the fish disease room, some of the fish from crosses are exposed to disease bacteria to determine resistance. That laboratory is strictly quarantined and access is limited.

Information about the lab’s research is disseminated through scientific publications and meetings with stakeholders that include the U.S. rainbow trout industry, with many large and small producers. “We’re a national center for the benefit of all,” he said. “Every five years, there is a program-planning workshop. We design the research for the next five years to fit what’s needed.”

The role of the lab, Rexroad said, is to conduct research that the industry can’t do—to complement the industry’s work, not overlap or duplicate it. Citing genetic research, for example, he said, “What are the traits in fish that are important to industry that are too difficult or expensive for the private sector to do?”

On the subject of consumer apprehension about genetic modifications and transgenic organisms, Rexroad said, “Our crosses are done the normal way. There is no gene manipulation or gene transfer.”

Rexroad reported that their scientists are all reviewed on the impact of their research on both science and industry. “We can transfer technology to industry,” he said. “Our goal is to give the fish to the people.”