Oxygen Uptake in A Spontaneously Ventilating, Blood-Perfused Trout Preparation

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Abstract
A spontaneously ventilating, blood-perfused trout preparation was used to examine gas exchange across the gills. The blood flow rate and input oxygen content to the branchial circulation were manipulated to assess the contributions of perfusion and diffusion limitations to oxygen transfer. Increases in the flow rate (Q), or the haematocrit (Hct) were positively correlated with increases in the oxygen uptake across the gills (Mg, Og, O2). Manipulation of pulse pressure or frequency of the pump, with no changes to Q had no effect on Mg, Og, O2. Addition of adrenaline (1 × 10−6 M) to the blood also did not effect Mg, Og, O2. Calculations of cardiac output from the Fick principle always yielded values which were overestimates of the actual cardiac output (Q) set by the mechanical pump. The difference between the measured oxygen uptake by the fish from the water (Vg1, O1, O2) and the amount of oxygen transferred to the blood across the gills (Vg1, O1, O2) was a reflection of gill tissue metabolism. It is concluded that trout gills, like mammalian lungs, are primarily perfusion limited for oxygen uptake under resting normoxic conditions, but decreases in diffusion limitations come into play under stress conditions, such as environmental hypoxia or exercise. Note: