Energetic cost of active branchial ventilation in the sharksucker, Echeneis naucrates.

1. Sharksuckers use active branchial ventilation when swimming or at rest in stationary water. When attached to a moving object or when placed in a water current, they shift to ram gill ventilation as water velocity exceeds a certain threshold. 2. Water velocities required for the transition from active to ram gill ventilation were from 10-50 cm s-1, depending on the size of the fish. 3. Oxygen consumption increased between 3.7 and 5.7% when the fish shifted from ram gill ventilation to active branchial pumping. 4. When water velocity was increased beyond the threshold for ram gill ventilation, no further increase in oxygen consumption was observed. 5. It is concluded that the energetic cost of active ventilation in sharksuckers is lower than has previously been reported for fish in general.