Oxygen consumption and apnoea in the shortfin eel,Anguilla australis schmidtii

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Abstract
Patterns of ventilation, oxygen consumption (VO2), blood gas tensions (PaO2 and PaCO2) and pH were determined in shortfin eels (Anguilla australis schmidtii (Phillips)). At rest, shortfin eels (average weight 646.5 ± 64.5 g) had a VO2 of 20.4 ± 1.2 ml. kg‐1.h‐1 (n = 13) at 17.5 ± 0.2°c, with smaller fish having the highest metabolic rates. The frequency of ventilation was inversely proportional to body weight in both A. australis schmidtii and A. dieffenbachii. In air‐saturated water 10 eels exhibited periodic apnoea (mean duration 3.59 min); periods of ventilation were more variable in duration (mean 4.92 min). After 2.62 min of apnoea, the PaO2 of dorsal aortic blood had fallen from 9.12 to 1.91 kPa. Thus, although the blood has a high affinity for oxygen and the haemoglobins are 30% oxygen‐saturated at this low PaO2, the eel allows its blood to be significantly depleted in oxygen during apnoeic pauses at rest. When ventilating its gills at rest, PaO2 does not approach the PO2 of the inspired water. It is suggested that these features of respiration in eels result in a saving of metabolic costs involved in ventilation. The results are discussed in terms of the eel's ability to withstand hypoxic conditions.