a b s t r a c tFish markets can be expanded by two means, first by attracting newcomers in a local trading room and secondly by allowing remote bidders to participate. In both cases, electronic systems have played a key role in French primary fish markets. The computerisation of trading rooms started in the mid 1980s while connection through Intranet or Internet systems first started in the mid-1990s and then has spread more actively in France since 2007. However, the socioeconomic impact (on prices for example) of expanding markets by electronic means is far from being clearly predictable. First based on an econometric analysis, this article presents evidence of increases in price level and variability after the implementation of local electronic auction systems. Secondly, a comprehensive survey of the 40 fish auction markets in France brings additional information about the effects of electronic remote bidding on fish prices. The analysis of these two empirical outcomes uses the cross-fertilization of the positivist auction theory in economics with the constructionist approach of Actor-Network Theory (ANT) in sociology to enrich the potential hypotheses lying behind the study of the structural impact of electronic systems on market prices.