You cook it for too long
Cooking fish too long will dry it out and cause it to lose its natural flavours. A good rule of thumb: Measure the fish at its thickest point and cook for 10 minutes per inch, flipping halfway through. The flesh should feel firm and turn from translucent to opaque or white, but still be slightly translucent in the middle. “Take it off when there’s just that little bit of translucency left in the middle,” says Randy Hartnell, former Alaskan fisherman and founder of Vital Choice, a website that sells fresh seafood. “You can apply this tip to almost any type of fish. If it’s almost done, it’s done.” For salmon, look for white lines to stand out. “When salmon is almost done, some of the proteins—which are a white colour—will begin to leak out of the fish because they’ve coagulated,” says Tentori.