Effects of Harvesting Waters and Storage Conditions on Yeast Populations in Shellfish

The yeast population in freshly harvested oysters. Crassostrea virginica , and clams, Mercenaria campechiensis , was limited to a small number of species. The yeast most commonly occurring was Rhodotorula rubra and the second was a Trichosporon sp. Concentrations of R. rubra increased in oysters stored as both shellstock and shucked at 7, 14 and 21 d at 2, 8 and 20°C. Oysters processed using a method similar to that used by most Florida processing houses and stored were found to contain higher levels of R. rubra than shellstock or shucked unprocessed oysters. Levels of R. rubra also increased in clams stored as shellstock. Correlation analysis of concentrations of R. rubra and selected physical/chemical parameters of the waters from which the shellfish were harvested showed a significant interaction between R. rubra and salinity. Fresh oysters harvested from high saline waters contained significantly higher levels of R. rubra than oysters harvested from low saline waters. Oysters collected from waters whose salinities were above 20‰ and stored as shellstock developed significantly higher levels of R. rubra than oysters from lower salinity waters. Processed oysters showed a similar response. The results suggest that R. rubra is part of the "normal biota" of Florida oysters and that the major factors influencing the development of this yeast in oysters are time and temperature of storage and the salinity of the waters which the oysters are harvested.