Alimentation expérimentale de l'huître Crassostrea gigas à l'aide de navicules bleues Haslea ostrearia (Simonsen) de différentes tailles

The influence on the feeding physiology (clearance, filtration, ingestion, absorption) of the Japanese oyster Crassostrea gigas of low concentrations of suspended particulate matter (SPM ranging from 2 to 20 mg.l-l) and high food quality (mean organic fraction =54 %) was studied in the laboratory. Experimental diets were made up with three strains of the "blue diatom" Haslea ostrearia, which is responsible of the greening of oyster-ponds. The strains were characterized by different sizes (48, 65 and 98 µm respectively) but possessed the same density and biochemical composition. Clearance rate was found constant at 2.2 1.h(-l).g-l dry weight and therefore was not influenced by increasing seston load. Pseudofaeces production was observed for SPM concentration adjusted at 2.1 and 2.3 mg.l-l, which suggests a decrease of the threshold of pseudofaeces production for diets having a high food quality. The effect of particle size on particle selection during pseudofaeces production was not demonstrated. Digestibility fluctuated from 60 to 90 %, but no differences between the three sizes were recorded. Total ingestion rate, which was regulated by pseudofaeces production, levelled off at 6.51 mg.h(-l).g-1• Organic ingestion and organic faeces production models suggest that physiological processes in the Japanese oyster lead to a constant organic absorption estimated at 1.22 mg.h-l.g-l in this study.