Pike-perch or zander. It is a river fish with delicate flavour. They can be differentiated from the perch by the relatively large space between their dorsal fins and their elongate, fusiform body, which is never so steeply arched behind the head as it is in the Perch. The flesh is firm and white with a stronger flavour than cod. It was introduced into the United Kingdom in the 70's and is in danger of wiping out native species of fish.