The detectable odor of ammonia, also known as the "fishy smell," is usually a sign of protein degradation in seafood, but not always. If the shrimp haven't reached their expiration date and you smell an ammonia-like odor, you may be smelling purge -- harmless, liquified amino acids that seafoods release in the package, similar to the pink liquid in a steak package.
Checking for Freshness
Check for sliminess on the shrimp, a telltale sign of protein degradation that usually appears in tandem with an ammonia-like odor. If the shrimp have a slippery film and an odor, toss them. You can usually keep fresh shrimp two days past their sell-by date.
Prepping the Shrimp
Rinse the shrimp under cold running water for several minutes and smell them. If they still smell like ammonia, you know the odor comes from the flesh, not any purge from the packaging, and you should toss them. If they smell fresh, you can proceed with any preparation in your repertoire.