Physiological Responses of the Crayfish Pacifastacus Leniusculus to Environmental Hyperoxia: I. Extracellular Acid-Base and Electrolyte Status and Transbranchial Exchange Available to Purchase

Extracellular acid-base and ionic status, and transbranchial exchange of acidic equivalents and electrolytes, were monitored in freshwater crayfish (Pacifastacus leniusculus’) during control normoxia (⁠ = 148 mmHg; 1 mmHg = 133·3 Pa), 72 h of hyperoxia (⁠ and 24 h of recovery. An initial (3 h) respiratory acidosis of 0·2 pH units was completely compensated within 48 h by a 50% increase in metabolic [HCO₃⁻+CO₃²⁻] accompanied by a significant reduction in circulating [Cl⁻]. In addition, the original increase in was partially accommo dated. The time course of transbranchial acidic equivalent exchange paralleled the change in extracellular metabolic base load with a significant branchial output of H⁺ during the first 48 h of hyperoxia. This was associated with net branchial effluxes of Cl⁻ and Mg²⁺. Unidirectional flux analysis revealed parallel reductions in Na⁺ influx and efflux during initial hyperoxic exposure, reflecting an alteration in exchange diffusion. The net Cl⁻ efflux was due to an initial increase in efflux followed by a reduction in influx. The reverse sequence of events occurred more rapidly when normoxia was reinstated: metabolic base was removed from the haemolymph and control haemolymph acid-base and ion levels were re-established within 24 h. Transbranchial fluxes of acidic equivalents similarly recovered within 24 h although net Na⁺ output and Cl⁻ uptake persisted.

The study attempted to identify relationships between branchial net H⁺ exchange and components of Na⁺ and Cl⁻ exchange and quantitatively to correlate changes in the acidic equivalent and electrolyte concentrations in the extracellular fluid compartment with those in the external water.