While conservationists invest heavily in the restoration of fish populations, the underlying mechanisms regulating fish abundance are still poorly understood. For instance, density has been hypothesized to be a chief regulator of population size through a potential impact on individual growth and survival of young-of-the year fish. However, the extent to which density influences individual growth and survival is uncertain. Furthermore, variability of responses to density between distinct populations remains poorly understood. I designed a large-scale field experiment to study the impact of density on individual growth and survival and the interpopulation variability of responses to density. I will manipulate the density of landlocked young-of-the-year brook trout (Salvelinus fontinalis) in isolated sections of four small streams at Cape Race, Newfoundland, and record individual growth and survival in each section over 6 weeks. I anticipate that this research will give insight into the mechanisms regulating population abundance and thus provide tools critical to the management of fisheries. More specifically, it will help assessing natural variations of population abundance as well as predicting the outcome of conservation efforts.