The role of body surfaces and ventilation in gas exchange of the abalone, Haliotis iris.

The archaeogastropod Haliotis iris possesses paired bipectinate gills and normally four to six shell holes. In still water, endogenous water flow entered the branchial chamber anteriorly to the left of the head and was exhaled primarily from the three most posterior holes. The first or second anterior aperture was occasionally weakly inhalant. Cardiac interaction superimposed an oscillatory component upon ciliary ventilation but did not augment mean flow. At normal endogenous flow rates 49% of oxygen was extracted from the branchial flow, increasing to 71% at lower flows. In still water, normoxic M(O(2)) was 0.47 micromol g(-1) h(-1). Oxyregulation occurred down to P(O(2)) approximately 80 Torr, with partial oxyregulation down to 45 Torr (P (crit)), and oxyconformity below this. The oxyregulatory plateau was absent in artificially ventilated animals but normoxic M(O(2)) was higher (0.65 micromol g(-1) h(-1)). Endogenous ventilation was unaffected by hypoxia to 15 Torr. Heart rate decreased by approximately 20% at 26 Torr before falling more steeply. Oxygen uptake from the branchial ventilation stream fully accounted for normoxic M(O(2)). In hypoxia (<30 Torr), no uptake occurred from the head or foot despite extensive eversion of the epipodium. Blood oxygen measurements excluded the right mantle as a significant gas exchange organ. Changes in oxygen uptake caused by changes in the velocity of external water currents support the concept of induced ventilation and suggest that in still water aerobic respiration was ventilation-limited. Although ciliary ventilation appears adequate to support resting aerobic metabolism, induced ventilation may provide increased aerobic scope for activity and repayment of oxygen debt.