The Ventilation, Extraction and Uptake of Oxygen in Undisturbed Flounders, Platichthys Flesus: Responses to Hypoxia Acclimation

Gill ventilation , extraction of O2 from the ventilatory current and O2-uptake were measured in three groups of undisturbed flounders naturally buried in sand. Two groups were acclimated to normoxic water . One was studied in normoxic water, the other during acute exposure to hypoxic water (P1, O2 = 30 mmHg). A third group was acclimated to and studied in hypoxic water. Gill ventilation was measured directly using an electromagnetic flowmeter. The flowprobe, fitted to a plastic funnel, was placed over the fish’s mouth without making physical contact with the fish. Exhaled water for calculation of O2-extraction was siphoned from another plastic funnel placed over the upper operculum of the flounder. Acute hypoxia exposure of normoxic fish caused nearly a doubling in ventilation volume. In flounders acclimated to chronic hypoxia and studied in hypoxic water the ventilation volume reached a value approximately 3-5 times that of normoxic fish. O2-extraction averaged 76% in normoxic flounders. During acute hypoxia the value declined to 52%, the same O2-extraction was obtained in the chronically hypoxic fish. for the normoxia acclimated fish in normoxic water was 0 · 45 ml O2 · kg −1 .min − 1 declining to 0-12ml O2.kg − 1.min − 1 during acute exposure to hypoxia. of hypoxia acclimated fish in hypoxic water was 0 · 24 ml O2. kg − 1. min − 1. When compared in hypoxic water, the hypoxia acclimated fish show an unchanged O2-extraction of 52% in spite of a nearly two-fold increase in ventilation relative to that of the normoxia acclimated fish. Possible causes for this may be a left shift of the O2-Hb dissociation curves and an increase in the transfer factor for O2 over the gills in the hypoxia acclimated fish.