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Dreissena polymorpha (Pallas), zebra mussels, are recent invaders of North American freshwater systems. They have a high reproductive rate and settle in high densities which can clog water intake valves and pipes. Many studies investigating the use of heat as a control measure have examined the effects of high temperatures on zebra mussel mortality. Much less is known about the effect of temperature on the actual growth rate and development of zebra mussels. This study examined the growth rates of zebra mussels at 10°C, 20°C, and 25°C over two four-week periods in the laboratory. Mussels were placed in culture dishes (five similarly sized mussels per dish) and fed 100 ml of the algae Chlorella pyrenoidosa (Chick) daily at a concentration of 4.13 * 105 cells/mI. Shell length and shell height measurements were taken three times during the experiment. Although shell length is the measurement typically used in growth studies, it has not been documented whether increases in shell length are accurate indicators of increases in tissue weight. This study compared both shell length and shell height with tissue weight. Since the correlation between shell length and tissue weight (r^2 = 0.811) was slightly higher than that between shell height and tissue weight (r^2 = 0.723), shell length was used as the growth indicator in this study. Growth was significantly greater at 25°C than at either 10°C or 20°C during one two-week period (Scheffe's, p < O.O5). Mortality was also significantly greater at 25°C than at 10°C. The results from this study are important because factors which reduce growth should decrease the long-term success of the zebra mussels and therefore should be useful as possible control methods. Also, scientists working with zebra mussels in the laboratory will find the results of this study useful in determining the best conditions in which to raise zebra mussels.



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