Maskinonge from three regions were studied: the Lake of the Woods district in Ontario (calledWestern); the Kawartha Lakes and Georgian Bay district in Ontario (Central) and the St. Lawrence River district in Quebec (Eastern). Examination of 202 stomachs, 81 containing food, showed the maskinonge to be a general carnivore, preying mainly on fish over 150 mm. in length. The families Percidae, Catostomidae, Ameiuridae, Centrarchidae, Hiodontidae, Esocidae and Cyprinidae were represented, along with at least oneCambarus. The yellow perch,Perca flavescens, was the species eaten most frequently in all three regions. A common white sucker (Catostomus commersonnii) was found in a stomach of the hybridE.masquinongy×E.lucius. Examination of the teeth of each specimen showed that they were being continuously replaced throughout the summer season.Rate of growth varied with sex and locality. Females had a significantly faster rate of growth, both in length and in weight, than did males. Maskinonge from the Western Region were shorter and weighed less than fish of the same age from the other two regions. Maskinonge of the Eastern and Central Regions reached the legal size of 30 inches fork length during their fifth summer, but in the Western Region they did not attain this size until their seventh summer. The length-weight relationship appears to be the same in the Eastern and Central Regions, whereas maskinonge from the Western Region tended to be heavier than those of comparable lengths from the other two regions. In all regions the length-weight relationship was a straight line when plotted logarithmically, its slope being estimated as 3.26 in the Eastern Region. Sexual maturity occurs first between the ages of three and six years, or about 575 to 800 mm. fork length. Specimens of aE.masquinongy×E.luciushybrid appeared to be infertile. They did not differ from the maskinonge specimens in their length-weight relationships but made faster growth than did the maskinonge from the same region.