Respiratory and cardiac function during exercise in squid

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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.

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