Salmon is a popular protein choice for those following a healthy diet. We typically cook salmon to 125 degrees for the ideal balance of firm yet silky flesh. But when it comes to wild salmon, we recommend cooking to 120 degrees instead. Why? Wild salmon has more collagen (and thus more connective tissue) and, more important, a significantly greater number of chemical cross-links between collagen molecules. When the wild varieties are cooked to just 120 degrees, the muscle fibers contract less and therefore retain more moisture. The leanest wild salmon also contains less fat, about half as much as farmed salmon, so there is less fat to provide lubrication and the perception of juiciness when cooked.
Source: America's Test Kitchen