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Black Gill

Additional Information

Black Gill in Georgia booklet
(Georgia Sea Grant and UGA Marine Extension Service, November 2013)

Monitoring the Health and Abundance of Georgia’s Shrimp
(GA DNR's Coastal Resources Division, November 2013)

"Black Gill in Georgia Shrimp," July 2015 (Produced by the Skidaway Institute of Oceanography in collaboration with UGA Marine Extension, UGA Public Service and Outreach, Georgia Sea Grant and the Georgia Department of Natural Resources.)

Affecting Shrimp in Georgia and South Carolina

Georgia Sea Grant and the University of Georgia are leading efforts to investigate the causes and impacts of black gill, a parasitic infection affecting many shrimp in Georgia waters. With funding from Georgia Sea Grant, UGA Skidaway Institute of Oceanography is collaborating with UGA Marine Extension Service, Georgia Department of Natural Resources' Coastal Resources Division (DNR) and several other organizations to conduct research on this condition. 

In 2013, Georgia shrimpers were catching far fewer shrimp, and many of those that were caught exhibited a strange darkening of their gills, a condition called black gill. Shrimpers contacted the DNR, UGA Marine Extension experts and coastal scientists for help in determining if black gill played a role in the decline in the number of shrimp caught. 

Black Gill: Another Challenge for Georgia's Shrimping Industry

Although evidence supports that the increase in incidence of black gill contributed to the disappointing 2013 shrimping season, unusually large amounts of summer rainfall in the region were also a significant factor. Heavy rainfall disrupted the movement of post-larval shrimp returning to their estuary nursery grounds, which is important for their development. The complex interaction between black gill transmission and other environmental factors, such as rainfall levels, complicates the research effort to determine the impacts of black gill on shrimp populations.

While black gill is clearly concerning to shrimpers, several other factors have been identified in the overall decline of shrimping on Georgia’s coast. The decrease in shrimp landings, while severe in 2013, is part of a long-term trend. In 2004, Georgia fisheries were worth a collective $10 million. By 2014, this value had dropped to $5.5 million.

What are some of the factors in the decline?

  • Decrease in the number of trawling licenses
  • Competition from foreign seafood imports
  • Increased operating costs for shrimpers
  • Maintenance costs of aging vessels
  • Higher incidence of black gill in shrimp

Industry value has dropped primarily due to a reduction in the number of trawling licenses issued and trips by shrimpers. In 1979, there were 1,471 commercial trawling licenses in Georgia. By 2014, this number dropped to only 253. Other economic factors have also contributed to the reduction in trawling effort in Georgia coastal waters, including aging vessels and fuel and labor costs. The average age of Georgia’s shrimp trawling fleet is over 50 years, requiring much maintenance to remain operational. However, the shrimping industry remains the most valuable commercial fishery in Georgia and provides a livelihood for many in Georgia's coastal communities.

Research Questions

Black gill had been observed in Georgia shrimp before the 2013 season. Shrimpers have been seeing blackened gills for years with increasing frequency. Black gill was first detected by DNR off the coast of Cumberland Island in 1996, but there has been much variability in black gill prevalence since then. From 2002 to 2014, the DNR has reported annual black gill prevalence ranging from 6.8% (2010) to 25.79% (2014), with no clear trend emerging. The monthly infection rate varies greatly with first reports typically occurring in August, peaking in September and October at over 40%, and declining to near zero with colder water temperature by December. The exact cause of the increase in black gill observations in recent years is complex and still not completely understood by scientists.

Read below for information on current questions that the black gill research team is answering.


The list of cooperating academic units and agencies in this initiative includes:

UGA Skidaway Institute of Oceanography
Georgia Sea Grant
UGA Marine Extension Service
Georgia Department of Natural Resources – Coastal Resources Division
Mercer University
Georgia Shrimp Association
Southern Shrimp Alliance
South Carolina Department of Natural Resources
Florida Fish and Wildlife Conservation Commission
North Carolina Division of Marine Fisheries
Southern Shrimp Alliance


For more info on black gill research in Georgia, contact Jill Gambill.