We use a spatially explicit modeling strategy in order to describe the dynamics of a bullhead population living in a river network in the South of France. We propose a multipatch Leslie model, which integrates the spatial heterogeneity of demographic rates and takes into account dispersion processes. The model is based on very first data coming from a field study. First, we test different hypothesis on survival (age variability, spatial heterogeneity, and density-dependence) and on dispersion (density-dependent recruitment of young fish) in terms of fit between modeled and field population features (population growth rate, local density, and spatial distribution). There, we show how such a model constitutes a tool to precisely examine the biology of bullhead. Indeed, the modeling approach leads us to operate a feedback from outputs of the model to biological assumptions. Second, we analyze the weight of dispersion in the population dynamics, which appears to affect seriously the spatial distribution of fish. Finally, we discuss our results in the framework of impact assessment of potential climate changes for the bullhead population.