Perch is an extremely common freshwater fish. It has six to eight dark vertical stripes and two separate dorsal fins, the front one having hard spines. One finds fewer perch in ditches and small waters than in the IJsselmeer and other large waters and rivers. The average length of perch is between 20-35 centimeters. When the fish is small, it lives in schools and eats zooplankton. Fish between 10 and 15 centimeters eat invertebrates such as opossum shrimp and gammarids. Larger fish switch over to hunting their own kind or smelt. They avoid ruffe and roach as prey. Older perch live alone in deep water.