Fishing in Stardew Valley isn’t easy, but there is one little trick you can use when trying to make the fishing meter stay below the fish and bring it to the surface. This minigame is essentially a challenge of keeping the green indicator (float) just below the fish. The fish will move up and down the meter, but if you can keep your indicator (which will naturally sink, but rise quickly with the tap of the mouse) on the fish.
It’s tempting to use fast clicks to make the indicator stay with the fish, but short sharp mouse taps make the indicator rise too quickly and you will lose your fish. Instead try pressing the mouse button down for longer, which slows the rise of the indicator and makes it much easier to keep the float near the fish. There’s also a timed component to fishing, which means if you mess up the position of the float too many times, you lose the fish anyway.
Practicing with the length of time you hold the mouse button down will increase your rate of fishing success, but fishing is hard nevertheless. It’s a skill you’ll have to actually physically refine, which makes the game a real challenge with actual player skills to master. Or a rage quit inducing torture fest. It depends on your perspective.