Abstract

Crayfish are successful colonizers of most freshwater systems and of many transitional (i.e. amphibious, estuarine) environments. Since freshwater, especially lentic, habitats are extremely variable, these animals must frequently encounter marked fluctuations in ambient temperature, oxygen, salinity, etc. while some species readily survive periodic drought. Recently several studies have been undertaken so ascertain the basic physilogical mechanisms which allow crayfish to compensate for, or acclimate to these fluctuating conditions of their natural habitat. Although in crayfish as in other crustaceans environmental change is initially perceived by environmental sensor systems, most physiological interaction with the environment, as well as much physiological compensation occurs at the gills. In crayfish these are complex, beautifully designed, aquatic exchangers which are responsible not only for exchange of oxygen and carbon dioxide but also for regulation of osmotic, ionic, and acid-base status, and for nitrogenous excretion. Many recent studies have concentrated on responses of one or other of these systems to environmental change but in fact a single step change in any environmental variable causes complex, integrated changes in most or all regulatory processes and thus each process cannot be studied in isolation. The present paper attempts to illustrate these integrated physiological responses with reference to several recent studies on crayfish acclimating to a variety of environmental perturbations.

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