ACTIVITY AND VENTILATION-INDUCED VARIATIONS OF POSTBRANCHIAL OXYGEN-TENSIONS IN THE ISOPOD SADURIA-ENTOMON

Variations in postbranchial oxygen tensions were studied in vivo in th e 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 ox ygen tensions, while a sudden burst of activity caused an immediate re duction in oxygen tension. Periods of no ventilation caused anoxic hae molymph in less than 3 to 4 min. Haemolymph oxygen tension responds ra pidly, within seconds to minutes, to changes in isopod activity. Oxyge n uptake rates calculated from oxygen tension difference, gill area an d 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 upta ke 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 in-trinsic diffusive conductance was estimated.