Respiratory and cardiac function during exercise in squid

Abstract

We investigated the cardiorespiratory performance of the squid Loligo opalescens at rest and during jet locomotion while tethered in an aquarium or while swimming in a Brett respirometer at speeds ranging from 0.05 to 0.6 m∙s−1. Simultaneous records of systemic heart rate and ventilatory frequency at each swimming speed were used with data for oxygen consumption to calculate the cardiac output and stroke volume. For a squid of mean weight 0.03 kg and length 0.18 m the resting heart rate averaged 60/min, the ventilatory rate was 26/min, and the calculated stroke volume was 0.05 mL (0.9 mL∙g heart−1) at 12 °C. During exercise the increased oxygen demand was accommodated by increases in both heart rate and stroke volume of almost 100% at the critical swimming speed of about 0.34 m∙s−1. Concomitant increases in the ventilation rate (350%) and ventilatory volume (500%) due to the requirements of jet locomotion were much greater than needed to deliver oxygen to the gills. At rest the oxygen extraction from the respiratory stream was 11%, and this declined to 5% at the critical swimming speed. The possibility that mechanical coupling of the circulatory and respiratory pumps may occur during jet swimming is examined.