The present study was addressed the following two
questions: 1. To which extent does the air-breathing
behavior of H. littorale may compensate the deleterious
effects of environmental hypoxia? The oxygen uptake
(V˙O2), the critical O2 tension (PcO2), the respiratory ( fR)
and air-breathing ( fRA) frequencies in response to graded
hypoxia were determined. 2. How is the fRA affected by a
combination of different sulfide concentrations and
hypoxia? The progressive exposures to increasing concentrations
(lethality) to sulfide concentrations under
normoxic and hypoxic conditions were determined along
with the fRA.