In its original habitat, the Ruffe has little prey, and resorts mostly to small insects or sometimes smaller ruffe. They seldom bother to eat eggs or any other species, making it a very small if not nonexistent predator in Europe and Asia. However, when put into the environment of the Great Lakes, the Eurasian Ruffe can become an overwhelming threat to other species. In rivers, the Ruffe prefers slower-moving water and in lakes it likes areas with soft bottoms and usually without vegetation. The Ruffe matures quickly, in 1-3 years, and therefore is ready to breed sooner. As soon as it has matured, the Ruffe breeds. The average female can produce up to 200,000 eggs her first round, which reduces to about 6000-5000 her second, third, and so on. However, it is still an astonishing number for one of these many fish to produce. The Ruffe also prey on salmon eggs. In 1989-1996, the Ruffe in the St. Louis River Estuary decreased the densities of several native fish.