Respiratory Metabolism and Swimming Performance of the Squid, Loligo opalescens

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Abstract
Maximum sustainable and burst speed, standard and active metabolic rates, and metabolic scope at temperatures from 7.5 to 17.5 °C were determined for the squid, Loligo opalescens, with a Brett tunnel respirometer. A comparison with sockeye salmon (Oncorhynchus nerka) of similar size at 15 °C indicates that squid have higher standard and active rates (254 and 862 mL O2∙kg−1∙h−1), but have sustainable speeds half those of salmon (0.36 m∙s−1). This confirms the low efficiency of jet-propelled swimming, and the resultant high cost of transport (12.5 J∙kg−1∙m−1; nearly 5 times that of salmon) raises interesting questions about how and why squid make large-scale vertical and horizontal migrations and the tactics they use to compete with fish that are both their predators and prey. Burst speeds after several maximal jets do not appear to be significantly greater than the peak speed after a single jet suggesting squid must depend primarily on maneuverability and high acceleration rather than high speed. A low capacity for accumulating an oxygen debt (73 mL O2∙kg−1) confirms predictions based on biochemical evidence. This debt is approximately equal to the energy needed to rephosphorylate muscle phosphagens.Key words: squid, swimming, oxygen consumption, oxygen debt, Loligo opalescens, metabolic rate, salmon, Oncorhynchus nerka