STORY LEAD:
A Better Way to Measure Catfish Feed Intake, Growth
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ARS News Service
Agricultural Research Service, USDA
Tara Weaver-Missick, (301) 504-1619, tweaver@asrr.arsusda.gov
August 4, 1999
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Tiny glass beads mixed with catfish feed are helping Agricultural Research
Service scientists track how food intake affects catfish growth.
Research geneticist Jeffrey T. Silverstein, based at the ARS Catfish
Genetics Research Unit in Stoneville, Miss., developed this technique. Until
now, it's been difficult to measure how much food an individual fish eats
daily, because all fish are raised together in a pond and fed
simultaneously.
It's easier to measure feed intake with land animals, because feed can be
weighed before and after, and then calculated to determine what each animal
consumed, according to Silverstein.
Generally, catfish producers record feed intake based on simple observation,
but this method assumes that fish consumed all the feed delivered and that
they all ate the same amount.
Silverstein adapted an innovative technique from salmon feeding
studies--tiny glass beads in the feed--and customized it for channel
catfish.
The opaque glass beads are about 0.4 millimeters in diameter. They are mixed
into the feed in low concentrations of about 1 percent of the feed. After
feeding, catfish are anesthetized and x-rayed. This allows the beads to be
counted so that an accurate feed calculation consumed by each fish can be
taken. Fish with superior feed intake and conversion of feed into filet meat
can be identified, so this trait can be incorporated into breeding programs.
Silverstein has perfected the technique even more by automating the bead
counting process. This allows him to view 600 scanned x-ray images a day,
versus 200 images over a few weeks when done by hand. Automation is nearly
100 percent accurate.
In indoor tank studies ARS scientists found different catfish strains
consume feed at different rates. This information will help them to make
genetic improvements in channel catfish.
An article on the research also appears in the August issue of Agricultural
Research magazine. The story is also on the World Wide Web at:
http://www.ars.usda.gov/is/AR/archive/aug99/feed0899.htm
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Scientific contact: Jeffrey T. Silverstein, ARS Catfish Genetics Research
Unit, Stoneville, Miss., phone (601) 686-3591, fax (601) 686-3567,
jsilvers@ag.gov.
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