We tested if within-lake differences in individual growth in an Arctic charr population before and after nutrient enrichment was due to a population bottleneck, for example as a result of strong selection for growth in a limited part of the population. The positive change in growth pattern after treatment was not coincident with a reduction in microsatellite variability, and various genetic estimators of demographic change did not indicate changes in population size. This suggests that the change in growth was not a result of only a limited part of the population responding, but an overall response.