This study aimed to model the food intake of P. margaritifera to examine the relationship between food level and reproductive activity. The effect of microalgae concentration on ingestion rate and assimilation efficiency was studied over a broad concentration range, using a mixture of Isochrysis galbana and Chaetoceros gracilis. Reproductive effort was assessed using three microalgae concentrations of 0.5, 7 and 18 cell lL À1 . Reproductive status was assessed by gonad development index (GDI)the ratio of the gonad surface to the visceral mass surfaceand histological analysis of the gonad based on the presence (continuous or discontinuous) or the absence of gonial cells (GC). Ingestion is a saturating function of seston concentration for bivalves modelled with an adapted Michaelis-Menten function. The maximum ingestion rate of P. margaritifera adults was 193.50 9 10 6 cell h À1 g À1 dw and the half saturation coefficient was 15 cell lL À1 . The concentration of 18 cell lL À1 , supplied for 45 days, induced a significantly higher GDI than the other treatments. GC decreased significantly and even stopped when pearl oysters were under-fed, suggesting that the mitotic process of the germinal stem cells was altered. Differentiation of germinal stem cells therefore appears to be controlled by food availability.

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