Phenotypic variation of walleye, Sander vitreus, in Canadian Shield lakes: New insights on percid polymorphism

Abstract

Literature on colour dimorphism in walleye has concerned only the blue form, Sander vitreus glaucum (formerly Stizostedion vitreum glaucum), historically found in lakes Erie and Ontario and considered to be extinct from the fish fauna since the 1960s. In this paper, we report unusual observations of a blue form of walleye living in sympatry with the yellow form, Sander vitreus (formerly Stizostedion vitreum), in five lakes of the Canadian Shield, northern Quebec. We compared head morphology, diet, and growth of the two forms to determine if there are any variations in characteristics other than colour and to examine the potential adaptive value of the two phenotypes. The blue form has a significantly longer head than the yellow form but does not differ in diet; the blue form also exhibits slower growth. The existence of a blue form of walleye in lakes of the Canadian Shield provides new insights into percid polymorphism and gives important information about their occurrence outside the Great Lakes area.