Chapter 4 - Feeding and Metabolism

Abstract

Pearl oysters are typical bivalve molluscs in the general morphology and functioning of their feeding, ingestion, digestion, defecation, and excretion. Like most other bivalve molluscs, pearl oysters are filter or suspension feeders throughout the free-living stages of their lifecycle. They filter fine suspended particles, seston, from the water around them. There are often significant amounts of dissolved organic matter (DOM) in seawater and this is another potential source of nutrients for pearl oysters. There are several factors that affect their ability to capture these particles and the nutritional value of the particles, that is, whether they are organic or inorganic, their abundance, size, shape, surface characteristics, density, digestibility, and biochemical composition. The energy-yielding oxidative processes of metabolism are usually aerobic in pearl oysters, although anaerobic metabolism may occur in some circumstances. Oxygen for aerobic metabolism is extracted from the water fl owing through the mantle cavity and CO2 is discharged. The gill filaments contain hollow tubes through which hemolymph flows and deoxygenated hemolymph thereby comes into close proximity with the seawater flowing over the filaments. There is reciprocal exchange of O2 and CO2 as they diffuse passively across the fine filament membranes according to the gradients between seawater and hemolymph.