Swimming Energetics of Striped Bass (Morone Saxatilis) and Bluefish (Pomatomus Saltatrix): Hydrodynamic Correlates of Locomotion and Gill Ventilation

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Abstract
Swimming patterns of striped bass and bluefish were monitored using a miniature accelerometer to record instantaneous acceleration and instantaneous deceleration during tail-thrusts over a wide range of swimming speeds. In addition, ventilatory excurrent flow patterns were visualized in swimming striped bass by injecting milk via a buccal catheter. Both species accomplish steady swimming with both symmetric and asymmetric thrusts; other transient swimming patterns were observed as well. Over the transition range from active branchial to ram gill ventilation, no measurable change in forward acceleration amplitude occurred with adoption of ram gill flow in both species; this can only occur if drag does not change over the ventilatory transition. From metabolic measurements and from implications about swimming drag deduced from acceleration amplitude, the cost of active ventilation just prior to adoption of ram gill ventilation was estimated to be 8-i % and 8-4% of total metabolism for striped bass and bluefish respectively. Ventilatory effluent flow patterns during cyclic ventilation in swimming striped bass induce substantial turbulence and probably boundary layer separation. Flow patterns during ram ventilation result in streamlined flow over most of the length of the fish. The results show that transfer from active to branchial to ram gill ventilation provides important hydrodynamic advantages to these fishes at cruising velocities.

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