Branchial ion uptake in arctic grayling: resting values and effects of acid-base disturbance

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Abstract
Techniques for the measurement of unidirectional flux rates in fish which require no anaesthesia or surgery are described. Resting values for Cl− uptake at 10 and 17 °C were 8·03 ± 1·11 and 13·52±0·95μ-equiv. 200 g−1 h−1 (±S.E.), respectively; and for Na+ the rates were 15·49±0·40 and 26·30±0·36, respectively. Hypercapnic acidosis caused an increase in Na+ uptake, presumably through Na+/H+ (or ⁠) exchange. It is suggested that this is a com-pensation mechanism leading to the increase in blood buffering observed in response to hypercapnia. Alkalosis was observed following acute temperature increase and was accompanied by an increase in the rate of exchange and also by an increase in Na+/H+ exchange. The role of these branchial ion exchange mechanisms in overall acid-base regulation is discussed.