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Reactional behaviour of two species of young crayfishes to different concentrations in chlorures (Zn, Cu, Pb and Cr) in option with breeding water is analysed. Discrimination capacity is more feeble with O. limosus. Physiological differences are confirmed by the raising of temperature or the presence of sediments. One interpretation of the ecological repartition of the two species A. pallipes and O. limosus is proposed on this basis.

The effects on the crab's respiration of the sublethal metallic concentrations are analysed upon in toto organic structures and upon their very sensitive organs in the best and stressing conditions of temperature and of salinity. There is a connection between the metallic concentrations causing respiration deteriorations and the bearable metallic concentrations (starting lethal thresholds). In the same way there is a good correlation between the level of bioaccumulation and the metabolic depletion of the tissues. It's well proved by this research that a lethal metallic concentration in the best conditions of temperature and of salinity can greatly reduce the ability of the population to survive in the natural conditions of thermic and salin stress.