U.S. doctors have used ultrasound for years to keep track of an
unborn baby’s size and
development. More recently they use it to identify organs and
diagnose diseases. Now
farmers use it on fish.

“We use ultrasound technology to determine the sex of channel
and blue catfish,” said
Dr. Gary Burtle, an aquaculturist at the University of Georgia
Coastal Plain
Experiment Station in Tifton, Ga. “That allows more efficient
reproduction and more
fish getting to the markets.”

In 1996, Georgia farmers sent about $20 million worth of catfish
to processors.
Nationwide, the farm catfish crop was worth more than $364
million.

Until now, the only effective way to know if a fish was male or
female was by
dissection — cutting open the fish to see the reproductive
organs. But that’s not very
efficient.

So why do catfish farmers need to know if they have males or
females in their ponds?

Burtle said new hybrids result in larger fish that can be more
disease-resistant. When a
male blue catfish is bred to a female channel catfish, a new
hybrid results: a blue
channel. This hybrid can grow 15 percent to 30 percent faster
than the parent species.

In the past, catfish farmers had to wait five years for the blue
catfish to mature sexually
to know if they had males or females. And by that time, the
farmer had paid to raise
fish he might not need.

When the two fish species are about a year old, Burtle said,
farmers can use ultrasound
equipment to separate the fish by gender into pens. Then they
can sell the female blue
catfish and the male channel catfish.

It costs about $1.25 per year to raise a catfish to maturity.

“This technique allows the farmers to market their fish earlier,
saving about $5 per fish
in carrying costs,” Burtle said. They can keep the fish they
need to breed
faster-growing hybrids and sell the others while they’re
young.

Those young fish hook diners, too. Most catfish lovers prefer
their catfish small,
especially their fried catfish. Some claim the milder meat
tastes sweeter. So the young
fish may reel in premium prices for the producer.

Extension experts say catfish is a fairly low-fat meat. It has
about the same fat content
as skinless white chicken meat.

“Fat content varies greatly with the cooking method, though,”
said extension foods
specialist Judy Harrison. “If you just can’t resist the crunchy
skin of fried chicken,
broiled or baked catfish removes the temptation.”