"This fish makes its home in cold water, giving it extra layers of fat. It temporarily increases your maximum hearts when used in cooking."
The Hearty Salmon (051 in the Hyrule Compendium) is a fish found in Breath of the Wild. This creature can be eaten to recover 4 hearts, and can be sold to shop-vendors all over Hyrule for 10 Rupees each. They are rarely found in bodies of water, the most common areas being the Tabantha Frontier and Hebra Mountains. Hearty Salmon can be used in many Recipes and will temporarily increase the maximum numbers of hearts when cooked in a recipe. If cooked on an open flame by itself, Link will receive a Roasted Hearty Salmon, which will restore 4½ hearts.