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

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Abstract
When exposed to gradually lowered PwO2 [external O2 tension] values, the brackish water shrimp P. 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 hemolymph has in normoxic condition a Cl- value of 408 mM .cntdot. l-1 (medium 250-275 mM .cntdot. l-1). The cbloride of the hemolymph decreased when PwO2 was lowered below circa 100 mm Hg. At PwO2 80 mm Hg (circa Pcr) the hemolymph Cl- begins to show a steady decrease to a new, lower and stable value. At still lower tensions hemolymph 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 hemolymph chlorinity.