The influence of hypoxia on the blood regulation of the brackish water shrimp Palaemonetes varians Leach

During periods of hypoxia in hypotonic media, Palaemonetes varians Leach showed an unimpaired regulation of blood chloride until some minutes before death. Heart rate showed no clear dependence on the water oxygen tension (P wO 2) and postbranchial haemolymph oxygen tensions slowly decreased during progressive hypopoxia from a normoxic level of ≈ 30 mm Hg until the animals turned opaque some minutes before they died. Blood pH increased in hypoxia, from 7.6 in normoxia to > 8 in P wO 2 10 mm Hg. Taken together, these data have been taken to indicate that the oxygen consumption rate at the critical point (MO 2 P cr) of this species is very low (P wO 2 = < 10 mm Hg) compared with other brackish water natantians studied. The ecological significance of this to the species is considered.