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Life-history reactions of a pumpkinseed Lepomis gibbosus population in north-eastern France exposed to heated waters were studied. The study was conducted from 2001 to 2003 in an artificial reservoir, adjacent to a nuclear power plant, in which water temperatures are cool in winter (8Á2-12Á4°C) and rise early in spring (April: 14Á7°C) nearly 5°C and 3°C over the temperature of its tributary, respectively. Fast growth among young-of-the-year, precocious maturity and short life span were observed, in contrast to related studies. The short life span appeared to be the price paid for early maturity in breeding fish, which suffered high mortality rates just after their first reproduction.

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Zebra mussels, Dreissena polymorpha, were collected monthly from a copper‐contaminated reservoir over a period of nearly 3 years. Copper concentrations in the organisms showed marked fluctuations reflecting changes in the water contamination. Bioconcentration patterns were influenced by the specific capacity of this sentinel organism to biologically integrate the continuously evolving water pollution; the sampling pattern, which inevitably introduced a certain subjectivity into monitoring results; and weight changes in the animals within the yearly cycle. Consequently, the successive monthly indications obtained with the zebra mussels provided a current biological assessment of a complex dynamic contamination situation. In a second experiment, caged mussels from three different populations were transferred for 3 months into the reservoir and sampled on six occasions. Mortality rates, attachment capacity, and a condition index revealed no substantial fitness disturbances in the transplanted organisms. Differences in dry weight throughout the experiment were attributable to the initial characteristics of each population. The influence of body mass on monitoring results was eliminated by replacing copper concentrations (μg/g dry weight) with copper burdens (μg/specimen). In terms of copper burdens, the three transplanted populations exhibited very similar metal patterns. Moderate quantitative differences between introduced and indigenous populations were interpreted as the result of physiological adaptation of the indigenous mussels to their contaminated environment. This study showed that the transfer technique with D. polymorpha is a useful tool for active biomonitoring programs.