The tidal rhythm of extracellular digestion and the response to feeding in Ostrea edulis

Under natural conditions, on the shore, there is a tidal rhythm for changes in pH, length, and protein and amylase content of the crystalline style of Ostrea edulis L. When oysters were kept immersed and fed continuously for 2 weeks, in the laboratory, the rhythm of extracellular digestion was lost. Oysters were fed discontinuously for 2 weeks, in the laboratory, with a 6 h-on, 6 h-off feeding regime. During the feeding period, the changes in pH, size, and protein content of the style were similar to the changes observed in the field over the period of high tide. It is our hypothesis that the tidal rhythm of extracellular digestion in Ostrea is not endogenous, but is controlled by feeding activity.