Swimming Ability of Juvenile Mactra chinensis by Pedal Flapping

Abstract

Swimming behaviour of juvenile Mactra chinensis was observed in the laboratory. Clams of 7–15 mm shell length swam by pedal flapping after launching from the bottom by leaping. The average swimming speed of 7–9 mm clams was 6.0 cm s^-1 and that of 9–15 mm clams was 7.8 cm s^-1. The average distance swum reached 17.4 cm. Larger individuals of 31–35 mm shell length class did not show swimming behaviour but they performed leaping. Swimming by pedal flapping extended the range of locomotive distance through the water column at least 4.1 times over that achieved by leaping. Therefore swimming is thought to be an adaptive behaviour to reduce the risk of predation and increase the chance to find a better place to burrow.