Oxygen consumption and ventilation in declining oxygen tension and posthypoxic recovery in epigean and hypogean crustaceans

Respiratory and ventilatory responses to declining O-2 tension and posthypoxic recovery were investigated in 3 hypogean and in 2 epigean aquatic crustaceans. The aims of this study were to determine how these species reacted to declining O-2 tension, to investigate their changes in ventilation and metabolic rate during progressive hypoxia, and to extend our knowledge on the fate of anaerobic end products during subsequent recovery. Hypogean organisms had normoxic O-2 consumption rates 1.7-3.5 times lower than the epigean species. All 5 crustaceans were able to main tain their O-2 consumption rates (1) at relatively constant levels and (2) independent of Po-2 between normoxia and the critical Po-2. Hypogean species also possessed lower critical Po-2 than epigean ones, which may indicate that these organisms are better adapted to low O-2 content and are better equipped to stay aerobic under hypoxia. For all species, posthypoxic recovery resulted in a high O-2 debt. The payment of this debt was smaller in hypogean than in epigean species. The main explanations of the lower O-2 debt shown by hypogean organisms are the lower energetic expenditures noticed during hypoxia, partly due to a decrease in locomotory and ventilatory activities.