Size variation among individuals born at the same time in a common environment is a common phenomenon observed in natural populations. The development of broad size distributions are suggested to result from mechanisms producing positive correlations over time in the change of size, i.e. growth depensation. For organisms living in seasonal environments variation in size may be especially important, due to size-dependent capacity to withstand winter starvation. Depending on the mean size reached in autumn, variability in life history among individuals can be crucial for whether a total recruitment failure will take place or whether some larger individuals can survive. To study mechanisms behind growth depensation we first investigated the influence of maternal effects and density on the development of size variation in YOY (young-of-the-year) perch (Perca fluviatilis). To study this we used large-scale mesocosms stocked with different densities of newly hatched YOY perch of different maternal origin. During the following larval phase initial size differences increased more at high than at low density. This was mainly a result of that small individuals grew substantially less under high densities while large individuals performed equally well independent of density. In contrast, when stocking pond enclosures with different densities of post-larval perch, their size distributions broadened more at low than at high density if allowed only to feed on zooplankton. However, when given the opportunity to also include a second resource (macroinvertebrates) initial size differences again increased more at high density. Mechanisms behind these experimentally observed patterns are suggested to include size- and density dependent responses to resource heterogeneity and differential timing of diet shifts mediated via feedbacks on shared resources.