We studied changes in the respiration rate in five species of freshwater bivalves as a function of animal age and size. The species-specific lifespan was calculated on the basis of the obtained data: Rubner's constant (Ru) and lifespan at standard temperature 20 degrees C (T20). The longest and shortest lifespan among the studied mollusks was specific for the pearl mussel Margaritifera margaritifera (Ru = 37 kJ and T20 = 36 years) and the freshwater mussel Anodonta anatina (Ru = 8 kJ and T20 = 8 years), respectively.