Total distance travelled by worms in relation to sediment composition. Groups size n=6. Sediment composition varies between groups from 0, 25, 50, 75 and 100% of fish feed . Control group corresponds to an absence of sediment. Average distances represented by bold horizontal lines: means were: for group 100% sand: 18mm;  14mm for groups 100, 75, 50, 25% and 8.67mm for the control group.