Environmental Reservoirs and Mortality Associated with Shrimp Black Gill

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Price, Ashleigh Rene
Frischer, Marc E.
Department of Marine Sciences
Black Gill
Commerical Penaeid Shrimp
Georgia Shrimp Fishery
Marine Infectious Diseases
Issue Date
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The Georgia commercial penaeid shrimp fishery has experienced a significant decline in landings since 2000. The cause of the decline is unknown, but coincided with the emergence of a new ciliate infection that causes tissue melanization, called Black Gill (BG). Shrimp Black Gill (sBG) occurs primarily from August through November and is absent during February and March. The absence of shrimp Black Gill during the winter indicates that the sBG ciliate is likely reintroduced annually through a reservoir. The effects of sBG on the shrimp host are unknown; though it has been hypothesized that sBG causes mortality in shrimp. The first focus of this study was to investigate the hypothesis that the sBG ciliate uses a reservoir(s) or second host when sBG is not observed in shrimp. The second focus of this study was to determine if BG causes mortality in shrimp during the months when BG prevalence is generally highest. A survey of crustaceans, water, and sediment was conducted to identify potential reservoirs. Samples were analyzed using a molecular diagnostic assay, followed by phylogenetic analysis of the 18S rRNA gene to determine ciliate identities. Five species of crustaceans were identified as potential reservoirs of the sBG ciliate. Water and sediment were not found to harbor the sBG ciliate. Laboratory experiments were conducted to determine if sBG causes mortality in shrimp by measuring BG prevalence, mortality, growth rate, and molting frequency. A significant mortality event occurred when over 80% of shrimp died. This study provides the first evidence that the sBG ciliate uses multiple species of crustaceans as reservoirs and that sBG causes direct mortality in shrimp. While many questions remain, this research indicates that sBG has contributed to the decline of Georgia’s shrimp fishery and informs future management decisions about the fishery.