Elimination of the gill worm Urastoma cyprinae (Graff) from the eastern oyster Crassostrea virginica (Gmelin) using different salinity–temperature combinations

Abstract

Urastoma cyprinae (Class: Turbellaria) is a facultative parasite of the eastern oyster Crassostrea virginica. Because the worms are clearly visible when present in oysters, they could conceivably have a negative impact on the lucrative half-shell oyster market. Our work examines the salinity and temperature tolerances of U. cyprinae to help formulate ways of eliminating the parasite from oysters prior to marketing. Isolated worms were exposed to salinities of 0‰ to 55‰ at temperatures of 5°C, 15°C and 20°C, and in infected oysters at salinities of 8‰, 28‰ and 55‰ at temperatures of 10°C, 15°C and 20°C. Findings reveal that the salinity tolerance of isolated U. cyprinae ranges between 12‰ and 40‰. In the case of infected oysters, two scenarios for the destruction of worms emanated: firstly, to depurate oysters for 2 days at a salinity and temperature of 55‰ and 10°C, respectively, or, alternatively, to expose oysters to a salinity–temperature regime of 8‰ and 20°C for 4 days. However, to eliminate all traces of dead worms from oysters, the optimal salinity–temperature combination was found to be 8‰ at 20°C for 8 days.