The Transition Between Branchial Pumping and Ram Ventilation in Fishes: Energetic Consequences and Dependence on Water Oxygen Tension

Abstract

Ram ventilation has been demonstrated in rainbow trout, Salmo gairdneri. The swimming speed eliciting the transition in mode of ventila-tion increased with declining ambient water oxygen tension . The mode of ventilation of fish swimming at a constant speed could be altered by controlled variations in . Oxygen consumption decreased by 10·2% when rainbow trout, swimming at a constant speed, shifted from active to ram ventilation. This difference can be ascribed to a lowering of the energetic cost of active ventilation as well as improved drag characteristics. Water velocity required for the transition from active to ram ventila-tion in the resting sharksucker, Echeneis naucrates, increased with decreas-ing . The results show that water oxygen tension is an important stimulus for setting the ventilatory mode in rainbow trout and sharksucker.