Starbound has you traversing through different planets in your journey through the universe. While on certain, aquatic planets, you might think to yourself, “How can I catch these fish?” The answer is the same as in real life: by fishing! Note that only certain species of fish can be caught with a fishing rod, and in order to see these fish swimming about, a fishing lure needs to be used on the water to attract them to you and your rod. You’ll also be closer to completing your fishing collection by catching each of these.
The fishing mini-game in Starbound works pretty much as you suspect it would. You’re going to drop the lure in the water and use the directional keys to control it. Move it left to go further out, down to descend, up to ascend, or right and you’ll reel it in. Make sure to use this when trying to attract a fish; moving the lure closer will guarantee they’ll bite. When they do, it’s time to start reeling while they’re not resisting. You’ll know they’re resisting because your fishing line will blink, it’s at this time that you’re going to want to not reel at all. Then rinse and repeat this process until the fish is caught!
Note that upgrading your fishing rod and getting different lures will change how difficult it is for you to catch fish, and the rarer they are, the harder they are to catch. Good luck out there as you try to catch the over 40 species of fish there are!