Respiratory and Cardiac Performance in Lolliguncula Brevis (Cephalopoda, Myopsida): The Effects of Activity, Temperature and Hypoxia

Lolliguncula brevis Blainville is a small euryhaline squid found at temperatures between 11 and 31 °C. Changes in V_O2, heartbeat and ventilation frequencies were observed throughout this temperature range and under a variety of conditions, including acute hypoxia and swimming by jet propulsion in a tunnel respirometer. Resting V_O2 showed a Q₁₀ of 1.47, and heart rate and ventilation rate Q₁₀ values of 1.92 and 1.73, respectively; oxygen uptake could exceed 1.01kg⁻¹h⁻¹ at 30°C even at rest. The squids regulated their oxygen uptake at all temperatures. Oxygen extraction rates were in the region of 5–10% in saturated water, increasing to 15–20% in hypoxic water or after exercise. One effect of this variability is that ventilation stroke volume can remain constant throughout the range of temperatures and oxygen concentrations that the animal is likely to encounter, a necessary condition since the ventilation stream is also the principal mode of locomotion by jet propulsion. Blood oxygen-carrying capacity (from the copper concentration) was 4.6 ± 1.8vols%. Cardiac output and stroke volume were estimated from the observed V_O2 values and heartbeat frequencies. Resting at 25°C, the output was close to 11.51kg⁻¹ body mass h⁻¹. The systemic heart of Lolliguncula weighed only 2.06 ± 0.62 g kg⁻¹. In exercise the cardiac output must exceed 14×10³ 1kg⁻1 heart mass h⁻¹, pumping more than the heart's own mass of blood at each stroke.