Ventilatory behaviour and chloride regulation in relation to oxygen tension in the shrimpPalaemon adspersusRathke maintained in hypotonic medium

Abstract

Abstract When exposed to gradually lowered PwO2 values, the brackish water shrimp Palaemon adspersus Rathke responds with an increased ventilation rate with maximum around PwO2 70–80 mm Hg below which the rate is rapidly lowered. Heart rate shows a steady decline with oxygen tensions. When PwO2 levels are subsequently increased again, ventilation rate shows a linear increase, but with a clear overshoot effect at PwO2 over 100 mm Hg. P. adspersus haemolymph has in normoxic condition a Cl− value of 408 mM · 1−1 (medium 250–275 mM · 1−1). The chloride of the haemolymph decreased when PwO2 was lowered below ca. 100 mm Hg. At PwO2 80 mm Hg (ca. Pcr) the haemolymph Cl− begins to show a steady decrease to a new, lower and stable value. At still lower tensions haemolymph Cl− decreased more rapidly and after 1–1.5 h Cl− reached isochlorinity in PwO2 25 mm Hg and less. This phenomenon is considered a re-allocation of energy from ion transport to other vital processes with the consequence of a gradual decrease in haemolymph chlorinity.