UGA researchers take cruise to examine local shrimp, black gill parasite

Our Changing Climate

SAVANNAH, Ga. (WSAV) — Researchers working with the University of Georgia (UGA) Skidaway Institute of Oceanography set off on a stakeholders cruise aboard the R/V Savannah to continue studying the black gill parasite.

WSAV joined the research crew on a crisp Wednesday morning as they departed the Institute’s main dock for their fall 2019 shrimp/black gill cruise on a day-long journey around the local waterways.

The cruise gave researchers a chance to monitor the prevalence of the black gill parasite, which has impacted shrimp off coastal Georgia. 

The black gill parasite is a single-celled animal, called a ciliate, explained Marc Frischer, a marine biology professor with the UGA Skidaway Institute of Oceanography.

“The black gill part is actually the shrimp’s immune system trying to defend itself from that,” Frischer told News 3.

The ciliate gets into the shrimp, and the shrimp’s immune system responds by trying to kill the ciliate by encapsulating it inside what’s called a nodule, Frisher said. 

Toxins are then released that kill the ciliate, and in the process, the shrimp’s gill turns black, which destroys the gill.

“The gill is how they breathe,” Frischer said. “If they have a destroyed gill, then they can’t breathe, they have less energy, they’re less able to evade predators that want to eat them.”

As the large blue research vessel pushed away from shore, the team briefed crew members on safety protocol, andFrisher, along with Mike Kendrick of South Carolina’s Department of Natural Resources, gave research updates. 

The R/V Savannah headed toward the commercial fishing grounds just off of Wassaw Island. 

While offshore, researchers sampled water, plankton, sediments and conducted their first of four 15-minute trawls to be conducted through the morning into the early afternoon at Wassaw Sound and the Wilmington River. During the trawls, crew and media members wearing hard hats and safety vests went out to watch the team lower a green fishing net out the back of the vessel.

Once the net was brought back up, the team sorted through and made a record of their findings, an effort that was led by John “Crawfish” Crawford, a public service assistant with UGA’s Marine Extension and Georgia Sea Grant.

The shrimp were then sorted out from the rest of the fish in a room inside the boat; this process was led by UGA researcher Tina Walters.

“We’re determining the sex of the shrimp, male or female,” Walters said as she examined small piles of shrimp. “Then, we’re separating them [based on] whether or not they have some black gill infection visible or not.”

Marc Frisher holds up a jar of plankton collected from one of the trawl.

At the end of the cruise, 12 randomly selected shrimp were to be sampled for molecular and microscopic black gill diagnostics.

“We saw what was expected,” Frisher said near the conclusion of the trip.

“About half the shrimp had visible black gill, and I’m sure when we get back to the lab, we’ll find that number is actually quite a bit higher.”

Researchers also observed what has been previously reported by fishermen — this season is currently a bit slow for shrimping.

“Most of the shrimp that are usually out into the commercial grounds offshore by this time of year are found still in the sounds, which are off-limits for fishermen now,” Frisher said. 

“That’s exactly what we saw; We caught most of the shrimp in the sound, less offshore where the fishery is happening, and not many anymore up in the rivers and estuaries.”

Researchers make note of their findings.

Black gill and climate change

Researchers have also noticed over time that there might be a link between black gill and the changing climate.

“We think, from looking at the records of data since black gill was apparent in the mid-1990s and before, that what it correlates best with are these climate indices that capture the larger climate trends as opposed to just changes in weather,” Frisher told News 3.

This chart shows the relationship between the Pacific Decadal Oscillation (PDO) climate index and the prevalence of shrimp with visible black gill in Georgia and South Carolina. (Credit: Dr. Michael Kendrick, South Carolina Department of Natural Resources)

The prevalence of black gill in shrimp correlates fairly well with those indices, he said.

“What that means in terms of the fishery, we don’t really know, except that this condition does seem to be correlated with climate conditions,” Frisher added.

Tina Walters holds up a shrimp infected with the black gill parasite.

He noted that the cause of black gill in shrimp has no impact on humans whatsoever.

“There’s nothing harmful or risky in terms of humans,” he said. “It’s not a problem to eat shrimp with black gill.

“In fact, if you’ve had shrimp in Georgia in the past 20 years, you’ve probably eaten shrimp that had black gill.”

Of Wednesday’s cruise, Frisher told News 3 that the point of such trips is to allow everyone involved in the industry, including researchers, press, shrimpers and the public, to interact and examine together what’s been seen thus far in terms of black gill prevalence.

“We had a good opportunity to have a lot of conversations, we had updates on what the research is telling us, what we’ve been learning, what we still don’t know and would like to learn, and where we’re going,” Frisher said. “I hope those messages are absorbed by the community broadly.”

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