The performances of planted brook trout (Salvelinus fontinalis) and F1splake (Salvelinus namaycush x S. fontinalis) were studied in four Precambrian Shield lakes. Splake survived better than brook trout in three lakes; mean gill-net recoveries were 15.3, 13.2, and 8.5% of plantings of splake compared to 2.9, 1.2, and 7.2% for brook trout. The fourth lake showed a mean recovery rate of 28% for both splake and brook trout. Most brook trout were caught in the year of planting or the year following, whereas the splake recoveries were spread over 6–7 years. Each kilogram of planted yearling splake yielded 2.5–7.1 kg among lakes; each kilogram of yearling brook trout planted yielded 0.2–1.3 kg. Brook trout and splake planted in the same lake grew at approximately the same rate in the year following planting. There were, however, differences in growth rate of both brook trout and splake among lakes and for splake the differences were maintained for an additional 5–6 years. Diet of both species differed among the lakes but brook trout fed more on aquatic insects and fish while small splake utilized Entomostraca (chiefly Cladocera) and larger splake preyed heavily on Malacostraca (chiefly crayfish) and fish (chiefly yellow perch, Perca flavescens).