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Muscling in on Meatier Trout

Rainbow trout's tender, delicately flavored meat is made of muscle. Some trout are better and faster than others at converting their feed into this tasty flesh.

Rainbow trout breeders may soon be able to more easily single out fish that have the genetic makeup to develop less fat and more muscle. That's thanks to new investigations by Agricultural Research Service fish geneticist Kenneth E. Overturf.

Overturf developed an RT-PCR assay, short for "real-time polymerase chain reaction," that correlates the presence of a telltale protein, myosin, to a trout's muscle growth. Test results should help breeders and researchers pinpoint fish that are best-suited to serve as brood stock, the parents of new generations of farm-raised trout.

Researchers have known of the correlation between myosin and muscle growth for decades. But Overturf and co-investigators are the first to use the connection for a fast, reliable lab test of trout muscle growth.

Overturf developed the test at the University of Idaho's Hagerman Fish Culture Experiment Station, about 90 miles southeast of Boise. A member of the ARS Small Grains and Potato Germplasm Research Unit, Overturf uses the RT-PCR test to learn more about the genetic makeup of fast-growing trout that muscle-up rapidly on environmentally friendly, grain-based feeds.

The experimental feeds that Overturf is scrutinizing are made in part from oats or barley. Faster-growing fish with a hearty appetite for grain could help fish ranchers meet the growing demand for farm-raised fish. Experts expect that U.S. aquaculture production will have to expand by 500 percent during the next 25 years to satisfy this demand.

Raising fish with a hearty appetite for grain also should lessen the risk of overfishing oceanic species, such as jack mackerel or menhaden. Today, these fish are among those used in fishmeal that feeds their on-farm cousins.

Overturf's research is profiled in the June 2003 issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research agency.