Unless the fish or seafood you’ve bought is literally the catch of the day, chances are it will smell and taste at least a little fishy, thanks to a compound found in nearly all seafood called trimethylamine oxide, or TMAO. This compound is odorless when fish and shellfish are alive, but once they’re killed, TMAO slowly transforms into TMA (trimethylamine), which has a fishy odor. Here’s a tip for how to remove the fishy smell from seafood.