Respiration of four freshwater species of the amphipod crustacean Cammarus: G.fossarum, G. lacusrris (river and lake), C.pulex and G. roeseli were measured in a closed, stirred respirometric chamber with a micro-electrode. Oxygen consumption, expressed as weight-specific oxygen uptake (R,) in relation to decreasing oxygen concentration, varied at air saturation from 0.86 ( C . lacusrris, lake) to 2.06 pl 0, mg-' AFDW h-' (G. pulex). R, also differed intra-specifically among the two populations of G. lacustris.
G. lucustris (river), C . pulex and G. roeseli expressed moderate ability to regulate their oxygen consumption at decreasing oxygen concentrations, whereas the regulation ability was higher in G. lacusrris (lake) and in C.fossarum, which maintain high oxygen uptake at oxygen levels > 2 mg O2 I-'.
All four Gammarus species are partial regulators in response to variations in oxygen concentration. The differences between species are considered too. small to account for their natural distributions. It appears that the tolerances of Gammarus species to organic pollution depend only in part on oxygen conditions.