Strong sour, ammonia-like, or rotten smell
Slimy, sticky, or tacky texture
Dull, gray, or faded color
Flesh that looks dry, mushy, or discolored
Eyes that are cloudy, sunken, or dull
Gills that are brown, gray, or slimy
Package that is swollen, leaking, or damaged
Excessive liquid or milky fluid in the package
Flesh that falls apart easily or feels unusually soft
Sour or off taste after cooking
Past the expiration or use-by date
Left out at room temperature for more than 2 hours
Stored in the fridge for too long
Frozen fish with heavy freezer burn or strong off odor after thawing