Sublethal energetic responses by Pisidium amnicum (Bivalvia) exposed to pentachlorophenol at two temperatures

Sublethal effects of pentachlorophenol (PCP) were studied in the freshwater clam Pisidium amnicum by examining the cause-effect relationship between PCP body burden and the rate of the whole animal heat output. In addition, the modifying effects of temperature (7 and 15 degrees C) and trematode parasites as natural stress factors were assessed. Results showed that even a low PCP body burden was sufficient to increase the heat output during the periods of aerobic metabolism and the magnitude of responses increased linearly with increasing body burden. During a valve-closure period, however, PCP had no effect on anaerobic heat output. The rise of the maximum heat output in response to PCP was more pronounced at the higher temperature. The response in heat output was similar in both infected and uninfected clams, but the general level of heat output was lower in infected clams. The increasing PCP body burden also increased the duration of valve-closure time. The results of this study suggested that microcalorimetry could be a useful tool in assessing sublethal responses by the clam, which offers several calorimetrically measurable parameters such as aerobic and anaerobic heat output and behavior.