Literature on the analysis of the decline of fisheries only emphasizes one of its structural components, either in the description of biophysical or in its social characteristics. Thus, this article aims to address the issue with a holistic approach that makes it possible to advance in the knowledge of inland fisheries as socio-ecological systems. Through the social networks analysis this article delves into the role that social capital and informal institutions play in the changes of bocachico fisheries, those that occurred between 1960 and 2015 in the El Llanito flood plain, Middle Magdalena Basin, Colombia.