Abstract
Variations in postbranchial oxygen tensions were studied in vivo in the brackish water isopod Saduria entomon collected from the Baltic Sea in 1992. Haemolymph oxygen tensions were highly influenced by activity. Resting isopods showed small and regular variations in haemolymph oxygen tensions, while a sudden burst of activity caused an immediate reduction in oxygen tension. Periods of no ventilation caused anoxic haemolymph in less than 3 to 4 min. Haemolymph oxygen tension responds rapidly, within seconds to minutes, to changes in isopod activity. Oxygen uptake rates calculated from oxygen tension difference, gill area and membrane thickness were compared with measured values. Permeability studies showed that only 30% of the gill area was effective in oxygen transfer. The present study has confirmed earlier measured oxygen uptake rates and reevaluated the role of the gills as respiratory organs. Postbranchial oxygen tension was established as a function of external steady state oxygen tensions and the intrinsic diffusive conductance was estimated.
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