Sand elimination by the asiatic hard clam Meretrix meretrix (L.): Influences of temperature, salinity and season

Abstract

Clams, being filter-feeders that burrow into sand, tend to accumulate sand in their body tissues. Depuration reduces the clams' gut contents and eliminates sand from different body fractions, providing some cleansing and ensuring that they are safe for human consumption. The Asiatic hard clam Meretrix meretrix (Bivalvia: Veneridae) is a commercially important species inhabiting sand flats of Hong Kong and Southeast Asia. In this laboratory study, the effects of temperature and salinity on the rate and profile of sand elimination in M. meretrix were studied during winter and summer using a 2 x 2 factorial design (i.e., two temperatures 20°C and 30°C, and two salinities 15‰ and 30‰). Sand removal rate was measured in terms of a decrease in inorganic content (i.e., ash) over a 72-h period. In general, sand was removed from the gut and body tissues and transferred to the external body fluid for subsequent discharge to the ambient water. Meretrix meretrix exhibited significantly lower sand removal rates in summer than in winter across all treatments, whereas the highest sand removal rate was observed at 20°C and 15‰ in both seasons. The sand removal rate of M. meretrix is, therefore, not only affected by temperature and salinity, but also strongly associated with natural, seasonal, effects. These findings have important implications for optimizing conditions for sand elimination of this species for the shellfish industry in Asia.