A population of the invasive Prussian carp (Carassius gibelio) was examined over a three-year period in a mesotrophic reservoir to find out interannual variations of fecundity and egg size and the influence of maternal condition (total length, TL, and age class) and environmental factors (water temperature and fish density) on these variables. Prussian carp reproduction was synchronous, with only a single batch, and fecundity ranged from 1,250 to 62,400 eggs per female. Relative fecundities and egg size showed no significant between-year differences. Fecundity increased with age, whereas egg diameter remained unchanged with age and TL. Fecundity was affected positively by TL and negatively by fish density, whereas temperature had no significant effect. Egg size was not affected by fish density or temperature.