Of all the animals that can be found in Breath of the Wild, the Stealthfin Trout might live up to its namesake the most, being a fairly difficult to find fish that only spawns in a handful of locations. Despite how difficult Stealthfin Trout are to find, they are one of the more useful food items in the game and are well worth tracking down whenever the player gets the chance.
Like most other varieties of fish in Breath of the Wild, Stealthfin Trout are only found in a select few locations in Hyrule, which can become a problem if the player needs to obtain a large quantity of them, although, thankfully, the areas that do hold fish tend to respawn them fairly quickly and aren't tied to Blood Moons like weapons and enemies are.
Where To Find Stealthfin
In order to find Stealthfin Trout, the play will need to have reached the Korok Forest, though they don't necessarily need to have navigated the Lost Woods. The easiest place to find Stealthfin Trout is in Lake Mekar, north and on the outskirts of Korok Forest, just south of Typhlo Ruins and the Ketoh Wawai Shrine. However, fast traveling to this location can take even longer to get to Lake Mekar than going around the long way, as the player will have to not only navigate the dark of the Typhlo Ruins, but also the swamp that encompasses it. With this in mind, it may be faster to travel to the Woodland Tower instead and walk around the outside, making sure to keep away from the Korok Forest edge as this will result in Link becoming "lost."
The second location to find Stealthfin Trout is inside the Lost Woods itself. Specifically, they can be found in Lake Saria surrounding the Kuhn Sidajj Shrine where players can also find Might Carp. This is the easiest place to look for Steathfin Trout, though there are only a handful present in this lake and the player will need to respawn them in order to get a decent number. This can be done by becoming lost in the Lost Woods, as, for some reason, this causes the fish in Lake Saria to respawn.
Stealthfin Trout are quite hard to see in the water under normal circumstances, as, especially in Lake Saria, they tend to blend into their surroundings quite well. However, like Sneaky Snails, they also glow in the dark when it is nighttime, so hunting for Stealthfin Trout at night is the best way to get the most out of fishing.
Consumable Effects
When consumed, Stealthfin Trout will heal Link for a measly one Heart Container, making it no better than any other uncooked fish in Breath of the Wild. While this alone would make it better to not consume if Link needs extra health on the fly, the fact that it can be very hard to find and gets a much better use out of cooking means that players shouldn't waste them on just any recipe and should stick to what they know works.
Stealthfin Recipes
The most obvious recipe for fish is Fish Skewers, which can be made by simply mixing any number of fish together in a cooking pot. When it comes to Stealthfin Trout, however, adding at least one to the recipe will also grant Link a stealth bonus, with this bonus increasing in potency the more Stealthfins are added to the recipe. While this can be a very handy food item to consume, it also doesn't make Link's stealth abilities any better than him simply wearing the Sheikah Armor, which the Steathfin Trout can also be used to upgrade.
Armor Upgrades
Cooking Fish Skewers may grant a fair few hearts when consumed, but Stealthfin Trout shouldn't be used for cooking. Instead, they are needed for the fourth and final upgrade to the Sheikah Armor set, which can be bought in Kakariko Village and can make performing sneak attacks much easier. On top of that, the Sheikah Armor also has a very useful movement speed increase during the evening and night that makes it the perfect armor to wear when exploring Hyrule after dark. While also needing Blue Nightshade, Sunset Firefly, Silent Shroom, and Sneaky Snail, the fourth upgrade for the Sheikah Armor requires a whopping 30 Stealthfin Trout and 15 Silent Princess, meaning any Stealthfin Trout that are found should be held onto until this upgrade has been taken.