Time spent by worms in the middle zone of the wells in relation to sediment composition (min; mean±SE; n=6). Sediment composition varies between groups from 0, 25, 50, 75 and 100% of fish feed. The middle zone was defined as the space between the first inner circle (4mm ø, around well center) and the most extern concentric circle (8th from the center, ø 36mm).