Black gill disease threatens Georgia shrimp
by Mary Landers, The Savannah Morning News
October 31, 2013 08:30 AM | 528 views | 0 0 comments | 16 16 recommendations | email to a friend | print
SAVANNAH, Ga. (AP) — This year was looking like a windfall for Georgia shrimpers. The production of Asian farmed shrimp was down after a bacterial infection swept through Thailand's ponds. The resulting shortage of imports drove prices up.

"Everybody was looking forward to fall," said Herbert "Truck" McIver Jr., a McIntosh County shrimper who works on the Sundown. "That's almost a guarantee. It would've been an awesome year with the price. Prices are probably like $1 more (per pound) than last year."

That's not how it's panning out.

Instead of celebrating, Georgia shrimpers are finding so few shrimp they're planning to petition for disaster status. And they're looking for answers to what's devastating the catch from Charleston to Jacksonville, a shrimp disease called black gill.

The condition, in which shrimp develop black spots on their gills, first showed up in Georgia shrimp in the 1990s. Since then it's waxed and waned, but the last several years have been bad ones, shrimpers say. This year up to 90 percent of the shrimp in some trawls have been infected.

Research from pond-raised shrimp indicates black gill has many causes, including bacteria, fungus, lack of nutrients, an overdose of copper or too much sediment. None of those are implicated in Georgia wild shrimp. Instead, the culprit is a single-celled parasite called a ciliate.

Too small to detect with the naked eye, ciliates are about 100 times bigger than bacteria, making them easy to see with a microscope. When infected with ciliates, shrimp fight back by encrusting the parasites inside the gills.

"They're putting it in prison," said Marc Frischer professor at the University of Georgia Skidaway Institute of Oceanography. The dark tissue of that encrustation gives the disease its name.

Infected shrimp speed up their molting process in an attempt to shed the parasite, a process that "takes a huge amount of energy," Frischer said. And the parasite ups the ante, too, by progressing to its free swimming stage in response to molting. The parasite then feeds off a molted shell and swims to a new host.

All the while, the gill infection is making it harder for the shrimp to breathe. The result is stressed shrimp that are vulnerable to predation.

Few shrimp lovers see black gill because shrimpers often remove shrimp heads, which contain the gills. The disease is harmless to people even if an infected shrimp is consumed.

"I ate them," Frischer said. "They tasted delicious."

Frischer and colleague Dick Lee are on the hunt for exactly which species of ciliate is attacking Georgia shrimp. Knowing the species, or at least what it's closely related to, can help answer questions about its behavior and life cycle and lead to its control or eradication.

DNA analysis is Frischer's approach. Because he's been unable to grow the ciliates outside of the shrimp, Frischer has had to separate the parasite DNA from the host DNA. It's not a simple matter.

He first chemically extracted all the DNA from a piece of infected gill tissue. Most of that DNA, of course, came from the shrimp. To separate out the parasite's DNA, he compared known DNA sequences from a database of more than 2,000 ciliate species to those of white, brown and pink shrimp.

Whatever appears only in ciliates would become his "hook" to separate fragments that came from the ciliate. That hook, which he thinks he's found, will allow him to identify a bigger fragment of ciliate DNA.

"Once a bigger piece is sequenced, we can compare it to known ciliates and can tell what group of ciliates it's in," Frischer said. "That will tell us about its life cycle, what it needs and where it's found."

Researchers also want to determine how infectious the parasite is, what affects its spread and how deadly it is to shrimp.

Research on black gill is moving forward with expected funding from Georgia Sea Grant. Along with Skidaway Institute researchers, collaborators include researchers from Mercer University, the Georgia and South Carolina Department of Natural Resources and the Georgia Shrimp Association.

Their results can't come soon enough for Georgia shrimpers, whose numbers are down from about 2,000 in 1979 to about 165 boat licenses issued this year, said Richard Puterbaugh, president of the Georgia Shrimpers Association.

Puterbaugh, who shrimped for 37 years out of Brunswick, sold his boat in 2010.

"(Shrimping) provided me a good life for a long time," he said. "I'd like to see it continue."

The shrimpers who remain have added their own observations, questions and suggestions to the research effort.

Some have asked if popping the heads off shrimp triggers the parasite to become free-swimming, just as molting does. Others want to know if the practice of throwing parasite-infected shrimp heads overboard spreads the disease.

Pat Mathews, owner of Lazaretto Packing Co., said many shrimpers fear that Georgia's current black gill problem came from shrimp ponds in South Carolina.

"All the pond-raised shrimp have had problems with diseases and viruses," he said. "Therefore, we need federal legislation preventing discharging these ponds into the ecosystem to prevent the spread to wild shrimp in the future."

Mathews worries that a moratorium on shrimping in the sounds — a move meant to provide a nursery area to sustain the fishery — is instead protecting the parasite in the undisturbed sediment.

It's another issue for fisheries managers and researchers to look into, said Frischer, who noted no data has been collected.

The black gill seems to have run its course for this season in Georgia. It's left shrimpers with empty nets and a lot of uncertainty, Peterbaugh said.

"Right now we have a lot more questions than answers," he said.

___

Information from: Savannah Morning News, http://www.savannahnow.com



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