Various terms are used to characterize fishers’ knowledge. Here we use situated fishers’ knowledge to refer to knowledge about long-distance fish migrations held by ethnic Lao fishers living in the Mekong River Basin in northeastern Thailand, southern Laos, and northeastern Cambodia. We consider the mobility of knowledge, humans, and fish, and adopt a theoretical framework based on Actor Network Theory (ANT) and political ecology. Based on fisher interviews, we demonstrate why knowledge transfer related to fish migrations is important. Fishers have various ways of knowing when migratory fish pass certain locations, although those are changing due to borders and technological changes. The paper’s main contribution is to move beyond simply investigating human mobilities, and to instead consider the relationships between human, fish and knowledge mobilities, something that ANT is particularly well suited for, due to its focus on multispecies interactions, something that mobilities scholars would benefit from paying more attention to.