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Respiration and Acid-Base Physiology of the Spotted Gar, A Bimodal Breather

1982; The Company of Biologists; Volume: 96; Issue: 1 Linguagem: Inglês

10.1242/jeb.96.1.263

1477-9145

Neal J. Smatresk, James N. Cameron,

Cardiovascular and exercise physiology

ABSTRACT In normally aerated water, at 20 °C, gar accounted for 42 % of their MO2 from their lungs, while in hypoxic water (PO2≃ 12 torr) their entire MO2 was from the lung, and O2 was lost through the gills. CO2 excretion in both normoxia and hypoxia was primarily via the gills. Lung ventilation increased 1150%, accompanied by an elevation of pulmonary perfusion from 5·9 to 12·1 ml · kg−1 · min−1 in hypoxia, which accounts for the enhanced pulmonary MO2. Cardiac output increased from 31 to 40·5 ml · kg−1 · min−1 and systemic perfusion was maintained in hypoxia. The difference in acid-base status between pre-and post-branchial blood (PCO2, pH and total CO2), changed only slightly during hypoxia, but the oxygen difference reversed. Normal dorsal aortic (DA) PCO2 was 23·8 torr, ventral aortic (VA) 20·3; during aquatic hypoxia the mean values were 21·9 and 22·6, respectively. Blood pressure rose in both the VA and DA in hypoxia but the branchial vascular resistance did not change. The oxygen transfer factor did not change significantly between normoxia and hypoxia. Anatomical studies of the gill microvasculature revealed a reduced and channelized lamellar circulation. No respiratory shunt pathways were found around the lamellae. The physiological and anatomical data indicated that the gar did not change lamellar perfusion or use shunt pathways to avoid hypoxic O2 loss.