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

Abstract

ABSTRACT Striped bass and bluefish use cyclic ventilatory movements to accomplish gas exchange at rest and slow swimming speeds, whereas at intermediate and high velocities, both species routinely shift to ram gill ventilation. Metabolic characteristics of the shift in respiratory behaviour indicate that as an animal adopts the ram mode, energy expenditure departs from an exponential relationship and increases at a shallow rate over the next 15 cm. s−1 range in speed. At higher, ram-supporting velocities, oxygen uptake increases once again at an exponential rate. Similar determinations of oxygen uptake at imposed swimming velocities in hatchery-raised rainbow trout reveal an exponential relationship over the entire swimming range. Trout actively ventilate their gills over this velocity range as well. In striped bass, the requisite trans-gill pressure for ram ventilation, as developed between the mouth and opercular door margins, is about 0·5 cm H2O. Critical swimming velocities for striped bass are 2·9–3·3 bl.s−1 while bluefish can maintain station at 4·0–4·6 bl.s−1. The adoption of ram gill ventilation is a velocity-dependent phenomenon over the size-range tested. Transfer of the work load of ventilation from the branchial to the swimming musculature results in substantial metabolic savings well within the cruising ranges of striped bass and bluefish. The savings probably accrue from cessation of rhythmic pumping by the branchial musculature and a change in overall body drag at ram-supporting swimming speeds.