Superb TroutIt's a Matter of Muscle
After egg collection, geneticist
Ken Overturf returns a female
brood trout into a raceway at
the University of Idaho's
Hagerman Fish Culture Experiment
Station. Overturf and colleagues
hope to breed fish that grow
faster on grain-based feeds.
Some fans of rainbow trout have dubbed their favorite
fish "nature's fast food." That's because it takes only a
few minutes to pan-fry, grill, or microwave this tasty fish.
Trout's tender, delicately flavored meat is, of course,
muscle. Farm-raised trout put on muscle as they swim against the gentle,
steady current that runs through the tanks, ponds, or channel-like raceways
they grow up in.
New studies should help researchers and rainbow trout
breeders more easily single out fish that have the genetic makeup to
develop more muscle more quickly. Agricultural
Research Service fish geneticist Kenneth E. Overturf is doing this
work with ARS and University of Idaho colleagues.
Of particular interest: trout that muscle up rapidly on environmentally friendly, grain-based feeds, made from oats or barley, for instance.
Geneticist Ken Overturf collects
immature trout, or fingerlings,
in the wet lab for weight and
other measurements to determine
how the fish use different feeds.
Why the need for faster-growing fish with a hearty appetite
First, to meet tomorrow's demand for farm-raised fish.
Projections indicate that U.S. aquaculture production will have to increase
by 500 percent over the next 25 years to satisfy America's needs. Second,
to lessen the need to harvest ocean fish, such as menhaden or jack mackerel.
Today, these species are key ingredients in feeds for their on-farm
Overturf, who is with ARS' Idaho-based Small Grains and
Potato Research Unit, has developed a high-tech test that sizes up a
key aspect of a trout's growth. The test correlates the presence of
a telltale proteinmyosinto muscle growth. Results give users
a valuable new way to pinpoint trout that have, in their genetic makeup,
a superior ability to convert feed into muscle.
He did the studies with rainbow trout at the University of Idaho's Hagerman Fish Culture Experiment Station, about 90 miles southeast of Boise.
Before taking measurements,
geneticist Ken Overturf (left)
and technician Dan Bullock
use a tag reader to identify
a female brood trout.
Overturf's test provides reliable results very quicklyand
doesn't harm the fish. It can be performed at a research laboratory
or at any commercial lab equipped to run leading-edge tests known as
real-time polymerase chain reaction (PCR) assays.
The test could identify the best-performing rainbow trout
as prospective super-parents, or brood-stock, of new generations. The
assay is based on a key fact that researchers have known for years:
myosin, the protein that's the basis of Overturf's new assay, is an
important part of muscle in fish and other animals.
Explains Overturf, "Trout that are active users of
energy from their feed and are vigorous producers of myosin develop
more muscle and grow more quickly. These fish also have less fat. That"s
because they're converting a large proportion of their feed into muscle,
instead of storing it as fat."
But why not simply eyeball trout, using fish size as a
potential indicator of continued fast growth? Because the biggest fish
aren't necessarily the best. "You can't tell, from their size,
which fish are the fastest at converting feed into muscle," says
Overturf. But his myosin assay gives users an inside look at this aspect
of a trout's genetic make-up. "Superior ability to produce myosin,"
he says, "is likely a gene-controlled trait."
Overturf's test is the first to use newly emerging real-time
PCR technology to assess how actively a rainbow trout's myosin gene
is working. Real-time PCR is named for the fact that it accomplishes
the many separate, time-consuming steps of conventional PCR all at once,
or in what is essentially "real time."
In related work, Overturf has created real-time PCR assays
for analyzing nearly two dozen other gene-derived natural compounds
in troutin addition to myosin. He's done some of that work with
his university colleagues.
These assays find, for example, key proteins in trout
that indicate a strong immune system, necessary to protect the fish
from viruses or bacteria.
The real-time PCR assays are a spin-off of efforts by
ARS researchers at Leetown, West Virginiaand by scientists elsewhere
in the United States and abroadto locate and decipher the functions
of all the genes in rainbow trout, called the trout genome. (See article
above.) Discoveries about the makeup of the trout myosin gene, for instance,
provided information Overturf needed to develop the myosin assay.
All the new assays from the Hagerman laboratory are "an
immediate, practical application of the rainbow trout genome investigations,"
says Lewis W. Smith, ARS National Program Leader for Aquaculture Research.
The myosin assay was also based, in part, on earlier studies
by Overturf and colleague Ronald W. Hardy, director of the Hagerman
station. The work yielded new details about the relation of myosin to
rainbow trout's prowess in converting feed to muscle. Overturf and Hardy
published their findings in Aquaculture Research, a British scientific
Wood, Agricultural Research Service Information Staff.
This research is part of Aquaculture, an ARS National
Program (#106) described on the World Wide Web at www.nps.ars.usda.gov.
Kenneth E. Overturf
is in the USDA-ARS Small
Grains and Potato Research Unit, c/o Hagerman Fish Culture Experiment
Station, 3059F National Fish Hatchery Rd., Hagerman, ID 83332; phone
(208) 837-9096, fax (208) 837-6047.
"Superb TroutIt's a Matter of Muscle" was published in the June 2003 issue of Agricultural Research magazine.