Sardines have natural variation and the fat content may range from 4-25%. Colder waters and recent feeding will result in a fattier sardine, while warmer waters and not having recently fed will result in a leaner sardine. If you open a can of sardines that seems messy and the skin is dislodged, this indicates very fatty sardines. Since the fat is just below the skin, the skin is dislodged as the fat liquefies during cooking. This fat is composed of long chain Omega‑3 fatty acids which are only available from fatty fish, shellfish, and marine algae. If you open a can to find beautiful, intact sardines, those are leaner and are higher in protein. The more sardines you eat, the more variations you will see!