The seafood market has changed substantially in recent decades, becoming increasingly globalized. This has led to introduction of new species and new sources of fish in most markets. We estimate a seafood demand system that, unlike models in previous studies, accounts for potential structural shifts caused by these market changes. We investigate the impact of tilapia as a new species and China as a new source on demand for imported whitefish in the United States. The results indicate that price flexibilities change substantially over time and that the structural shift takes place over a prolonged period.