The presentation analyses a case involving a change of scale in local food systems, namely, a "mega fish-box scheme" set up among five fishing vessels and about 1500 households in the area of Nantes, in France. Fishermen are located in an island (Yeu, in Vendée) and are involved in sustainable fishing methods. They are small size businesses with boats ranging from 12 to 20 m and crews not exceeding 5 persons including the skipper. The authors describe the people and devices that made possible and shaped this mega scheme. They specify the points on which the market mediations that were established generated alternativeness and the points on which they are sources of more conventional ways of operating. They have collected data which allow them to compute the value added and the way it is shared along the value chain. It is shown that the scheme is based on the coexistence of three rationales. Price formation at the upstream stage of the value chain results from supply and demand confrontation at the auction market. At the retail level, price is based on fair trade principles which imply that it is agreed in advance and enables fair payments to producers. Finally, the way margin is shared among the members of the crew is not driven by a capitalistic exploitation idea but by social considerations which lead to an egalitarian distribution. The analysis sheds in light that, far from generating conflicts of interest, the interaction between these three seemingly contradictory rationales, illustrates the willingness of the stakeholders to reach a compromise that is acceptable to all.