The effects of egg size on early development and growth of steelheadOncorhynchus mykisswere recorded for more than 200 days following hatching. Fish from smaller eggs hatched sooner and at a smaller size than fish from larger eggs, but fish from smaller eggs showed consistently higher growth rates than fish from larger eggs. Since many life‐history attributes appear to be determined by size or growth rate at age during the first year, egg size could be a significant predictor of important changes in the life history of individuals.