From: Martin Hugh-Jones email@example.com
From: Chan Yow Cheong, PhD firstname.lastname@example.org
ProMED-mail Regional Moderator for Asia
-->Date: Fri, 10 Dec 1999 From: Marjorie P. Pollack email@example.comSource: Associated Press 30 Nov 1999 [edited]
Hamburger gill disease, catfish - USA
A Georgia researcher has discovered a common minnow can help protect farm-raised catfish from hamburger gill disease, which costs the industry between $50 million and $100 million a year.
Farm-raised catfish have become the fifth most popular food fish in the United States. The industry supplied only 6 million pounds in 1970, but now produces more than 525 million pounds worth about $592 million each year.
Gary Burtle, an aquaculture specialist at the University of Georgia's Coastal Plain Experiment Station in Tifton, has demonstrated that flathead minnows, a common, inexpensive fish bait, offer protection from the hamburger gill disease.
"From the reports I get, it works, but it's not 100 percent,'' Burtle said. "We haven't totally solved this problem, but we have reduced the severity of the infection.''
Hamburger gill disease can kill an entire pond of catfish in as little as 3 days. It damages the gills, making it tough for the fish to get enough oxygen. They eventually suffocate. It is the fourth most common fatal catfish disease.
During his tests, Burtle discovered an almost invisible worm, about a half-inch long and thin as a human hair, harbors the parasite causing hamburger gill disease.
"If you build a pond, you probably will have these worms,'' he said, noting the worm population seems to be higher in freshly dug ponds, or ponds having been emptied and refilled.
The worm, known as _Dero digitata_, is found all over the world. It is a host for a protozoan releasing spores. The spores get trapped in the catfish's gills, leaving them looking like hamburger meat.
"We tried to find chemicals to combat the parasite, but we decided chemicals that would kill the worms would kill the catfish,'' Burtle said. "We looked for a fish that would be very effective at seeking these worms out in the mud. The carp was best, but it grows large and would compete with the catfish for feed.''
Then he decided to try the flathead minnow, which is in the carp family. The 2 1/2- to 3-inch (8-9cm) minnow is olive drab on top and white on the bottom.
"We place them in beakers with the worms and they eat them in seconds,'' Burtle said.
Fish farmers are already using the minnows in Georgia, South Carolina, Arkansas, Alabama and Florida, Burtle said. He recommends about 10 pounds for each acre of pond.
Burtle said fish farmers could conduct monitoring programs to detect the worms, but they would be considerably more expensive and time consuming.
"We're suggesting they stock the minnows,'' he said. "They take about a month to reduce the population to a non-threatening level.''
[We have the scientific name of the worm vector but not of the actual parasite that does the damage. Could it be _Trichophyra_? Can anyone help? - Mod.JW]