ABSTRACT
Alan Heath provides a discussion of the physiology of fish and their usefulness in studying the health of ecosystems. Pierre Mineau focuses on biochemical and physiological biomarkers; he discusses pesticides and songbirds, using cholinesterases, a favorite class of enzymes of mine, with the actions of fenitrothion as examples. Perhaps there are different acceptable definitions for health at each level of the hierarchy of life. Optimal biodiversity and existence of trophic levels could apply to an ecosystem or an individual habitat. The appropriate role of physiological and biochemical biomarkers in the study of multiple stressors and their importance in present and future environmental management decisions is discussed. Optimal reproduction and maintenance of a normal physiological state could be applied to the individual animal, plant, or protistan; the absence of overt pathology would be suitable for the organ and cellular levels, and the relative minimization of entropy production would be a characteristic of "health" on the thermodynamic level.
