| Abstrakt: |
Factors that make fish particularly vulnerable to the effects of environmental acidification during their first year of life are examined. This perspective is based largely on the results of research carried on concurrently in the field (the Little Rock Lake, Wisconsin, acidification study, 1984-1990) and in the laboratory using water tailored to mimic that of Little Rock Lake. We discuss ways in which seasonal changes influence both the environmental challenges encountered by fishes and their ability to deal with those challenges. The vulnerability of a species may be based as much on its life history (e.g., synchrony of sensitive or resistant life stages with maximum pH challenges) as on its anatomy and physiology. The ordering of acid sensitivity of species or of life stages is based on a dynamic balancing of energy and ion uptake, storage, and loss. These processes, in turn, are linked to the length of the growing season (net uptake phase) and the winter fasting period (net loss phase). Each species and each life stage varies in its capacity to achieve this life-sustaining balance of energy and ion flux. The season and environment have an influence both on the acid challenges present and the ability of each species and life stage to cope with those challenges. One consequence of seasonality is that, in northern latitudes, the embryo-larval stage (generally considered to be the most acid sensitive) may not be the stage most susceptible to the effects of low pH. Rather, the first-year overwintering juvenile stage may be the most vulnerable, often as a result of chronic ionoregulatory failure involving damage to gill chloride cells. Anthropogenic factors are bringing about environmental changes at rates that exceed the capacity of many organisms to adjust to them, especially early life history stages. Our results support the view that aquatic toxicological studies would often benefit from increased attention to interactions involving the season, the water chemistry, and the life history stage that is present. [ABSTRACT FROM AUTHOR] |
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