a1 Joint Nature Conservation Committee, Monkstone House, City Road, Peterborough, PE1 1JY
The capacity for oxygen uptake of a respiratory organ can be estimated using morpho-metric techniques, the two essential measurements being respiratory surface-area and thickness of the tissue barrier across which oxygen diffuses. In cephalopods, the gills are the main site of respiratory exchange and this study was designed to estimate oxygen uptake capacity of the gills of four different genera of cephalopods. A preliminary study was required to determine the form and structure of the gills. Light microscopy showed the surface of the gills to be highly folded, particularly in Octopus. A level of microscopy was chosen at which the outline of the smallest folds of the epithelium and the blood vessels of the gills could be easily resolved. Stereological techniques were then employed to obtain values for the respiratory surface-area related to body weight (cm2 g-1), tissue barrier thickness (μm) and oxygen-diffusing capacity (ml O2 min1 Torr·1 kg1). Values for these three variables obtained for the different species were as follows: Octopus vulgaris 2·9 cm2 g-1, 10 μm, 0·05 ml O2 min-1 Torr-1 kg1; Alloteuthis subulata 10·6 cm2 g1,6 μm, 0·27 ml O2 min-1 Torr-1 kg-1; Nautilus sp. 4·9 cm2 g-1,15 μm, 0·05 ml O2 min-1 Torr1 kg-1; Sepia hatchlings 13·3 cm2 g-1, 4 μm, 0·52 ml O2 min-1 Torr-1 kg-1.