How sustainable is salmon aquaculture? The criteria for responding to this question are set by different organisations, since the concept of sustainable aquaculture is a social construction and there are no agreed criteria for establishing this sustainability condition and its evolution. Using an historical political ecology perspective, this paper unravels the evolution of this social construction over the past 50 years in order to establish how sustainability, responsibility, and sustainable development have been (re)constructed over time in response to changing demands. These constructions are traced through scientific publications, business reports, international organisation literature, and in terms of regulatory and consumer pressures. The documents provide evidence of the ways in which the sector evolved a particular conception of sustainability alongside the emerging global agenda set in motion by the Stockholm Conference of 1972, precisely at a time when the collapse of many capture fisheries became evident and aquaculture was presented as a more sustainable alternative. The conclusions point to the importance, for the sector, of restricting the sustainability concept to a narrow definition of business responsibility based on eco-efficiency, bio-security, and innovation, and separating this responsibility from the broader-based concept of sustainable development promoted by most UN agencies, governments, and NGOs.