While fishing is an everyday activity in, catching all four Legendary Fish is easier said than done. Each fish corresponds to a different season, so you'll have to play the game for at least one full in-game year before you're able to even have the chance to catch them all. On top of this,you can't catch them until you're Fishing rank 30, so you'll have plenty of practice by the time you find them.
In order to get started, you'll first need to get a Fishing Rod. You can buy a Worn Fishing Rod at the Tackle Shop, but it'll set you back a pretty penny at 500 Tessarae. Instead, wait a bit until you can craft your own Fishing Rod. Once your Town Rank increases to Stone, you'll unlock the Mines and be able to mine Copper, which can be crafted into a Copper Fishing Rod. Get your Fishing Rod however you'd like, and then you can begin your fishing journey.
Void Salmon are an elusive reddish-purple fish in Stardew Valley found in only one location in the entire map, but they are hard to access initially.
You'll need to be Level 30 in Fishing before you'll even be able to catch the Legendary Fish, so make sure you spend some time early on getting this rank up. Fishing is a pretty slow skill to level, so unless you're a big fan of grinding, this is a bit easier to do over time rather than all at once. Thankfully, there is no mini-game associated with fishing, so each catch is a guarantee as long as you hit the button on time.
Once you've reached Level 30, there's one more thing you'll need to do. Head to Caldarus' Statue on your farm and interact with it to unlock the «Legendary» perk. This makes it so that the Legendary Fish will spawn.
Now that you're able to catch the Legendary Fish, it's time to head out. Rather than going on a hunt and mindlessly fishing until you catch what you're looking for,keep an eye out for in-game notifications alerting you that a Legendary Fish is nearby. Once you see that notification, head out with whichever rod you've got and start fishing.
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