Stardew Valley: Fishing
How to Play the Fishing Mini-Game
Fishing is probably the single hardest aspect of Stardew Valley, because it's not immediately obvious how it works. Worse, players may get discouraged because a hard-to-catch fish appears on their line, and they were never meant to be capable of catching it so early in the game. This tutorial explains the basics of the fishing minigame so that you can actually catch fish.
How to Catch Fish
Cast a Line
Head to the ocean or a river with your pole equipped. Press the action button and a meter will pop up. The fuller the bar when you hit the button a second time, the further your line will be cast. The bobber will attract different fish based upon where it lands. Further out from land is better and usually has better catch rates. That's a good rule of thumb, and finding spots where you can cast far from land will serve you well. An example of this is the left side of the docks on the beach.
Wait for a Hit
Now you'll usually have a hit within 10 seconds. Wait for the sound and visual indication (an alarm of sorts) and press the button once more. You'll begin the fishing minigame if you've got an actual fish on the hook. Sometimes, you'll just reel in some seaweed.
Fishing Mini-Game Objective: Keep the Bar Behind the Fish
The fish will go up and down on the bar, and you've got this green box you can control by pressing the action button. Your goal is to keep the fish inside the green box. While it's in these boundaries, the main meter will fill up indicating you're catching the fish. Should the fish leave, the meter will begin to drain, you'll hear a sound and the box will dim until it's behind the fish again. When the fishing meter is full, you've caught the fish.
Here's the main problem though - the fish is going to move, meaning you have to apply the right amount of virtual 'pressure' to the line. It may move up or down and maybe even trick you by bouncing around rapidly and erratically. These movements will come to indicate different types of fish. This is why newcomers shouldn't get too discouraged when a fish seemed impossible to catch - it may have been a legendary fish, and you're a newbie fisherman!
Moving the Green Box
Moving the bar upward means pressing left-click on the mouse or hitting the action button on the Xbox controller. Holding the button will make it rise rapidly, and letting go will cause it to fall. So how do we keep it in one spot? We click or press the button repeatedly in a rhythm so that the bar is neither rising nor falling. Click a little faster, it'll go up. Click a little slower, it'll go down. So hold to get it to rise a bit, then begin clicking to keep it in the correct spot and adjust accordingly!
If the fish goes down, you let up on the clicking a bit. If the fish goes up, hold and click. You'll learn to control the rhythm of the green area. It has a bit of momentum to it. If the fish goes all the way to the bottom, it can actually be hard at first because the box will 'bounce' when it hits the bottom. Applying a little pressure just before it hits the bottom will make it bounce less. When fish and box are both at the bottom it's very easy to reel it in - it happens automatically, and the fish can only go up, so you can wait on that and react accordingly.
Hopefully this helps you catch some fish in Stardew Valley. Each level of fishing will increase the size of the green area, so it makes it a bit easier to catch the average fish. You'll have access to tackle that helps immensely once you're in the levels 6-8 and have an Iridium Fishing Pole. Eventually you'll get good enough to catch Legendary fish.
Your character will gain fishing skill experience with each successful catch. At level 2, you can start crafting/buying bait to put on the fiberglass fishing pole you can buy from the man in the shop by the docks. This increases the rate of bites, so you can catch much more fish in a day. It consequently makes fishing less boring, as there's less wait time between attempts. Have a look at the How to Use Bait page for more information on bait and the tackle you'll unlock at level 6.