Studies on price trends of seafood products in the medium run remain scarce. In this paper, we investigate changes in first-sale prices of fish sold in France over the last 25 years. Drawing on the index number literature, we construct monthly chained fish price indices which are free from seasonal fluctuations. Our empirical analysis relies on a dataset including 126 million transactions completed in all French fish markets from 1994 to 2020. We show that first-sale prices of seafood products have substantially increased in the medium run, more than the inflation rate, except during the economic crisis from 2007 to 2009 and recently in 2020 due to the Covid pandemic. However, those higher prices have not always led to an increase in sales revenue of fishermen because of the continuous decrease in fish catches. In particular, the economic situation of fisheries has substantially worsen since 2017.