When you season canned or fresh fish with sugar, it helps mask any fishy flavors, enhances caramelization in the pan, and results in crispier skin without burning.
Since fish develops its golden brown crust at around 300 degrees Fahrenheit and sugar caramelizes at about 200 degrees Fahrenheit, adding sugar will jumpstart the browning process.
This gives your fish a crispy exterior while reducing the risk of overcooking. Additionally, the reduced exposure to heat will help your fish remain juicy and flavorful.
For canned fish, which is often packed in water, use half a teaspoon of sugar for every 5-ounce can. For fresh fish, add half a tablespoon of sugar to just one side of the filet.
Then, cook your sugar-seasoned, fresh fish in a pan with its sugar-coated side facing down. The direct heat will caramelize the sugar, giving you that perfectly crunchy crust.
Let the fish cook through in the pan without flipping it. Once done, transfer it to an oven at 425 degrees Fahrenheit and cook the rest of the way using gentler, indirect heat.