Abstract
The subject of the study was four populations of signal crayfish from Naryjska Struga River and lakes Pobłędzie, Mauda, and Staw Płociczno. The morphometric differentiation of female and male signal crayfish was studied with discriminant analysis. It was confirmed that both females and males from the Naryjska Struga River differ from the crayfish from the three lakes. The characters that best discriminated females were those associated with the cephalothorax and cheliped width, while in males they were those associated with the chelipeds and the abdomen.