The Gulf of Alaska and Bering Sea pollock fisheries in the U.S. were certified by the Marine Stewardship Council (MSC) in February 2005, yet to date little other than anecdotal evidence exists to suggest whether products from these fisheries have gained market benefits relative to uncertified pollock from, for example, Russian fisheries. This paper tests the hypothesis of structural change to determine if certification improved market shares for certified frozen pollock products at the expense of non-certified and reduced price substitutability between certified and uncertified products. We use a linear first-differenced inverse almost ideal demand system, where the possible dynamic effect of certification is captured using a logistic function of a gradual shift in market share over time post certification. The analysis is applied to German imports of frozen pollock from the U.S., Russia and China, since Germany is one of the more important markets for pollock in Europe. Results indicate that a statistically significant structural change did occur coincident with certification, with half of the adjustment by early 2006. In addition, results show that Russian pollock became less substitutable with US pollock after certification.