From Florensipedia

Players fish mainly to sell or use the Dissolution Pearls they catch. While the other Junk items can be sold to accumulate some Gelt, fishing can be done right next to water. A popular spot is Roxbury E5. You can fish "AFK" for however long you want, but you will stop fishing if you move, use a skill, if your inventory is full, or if you run out of bait. "AFK Fishing" is fishing when you are not at the keyboard. It is done by buying a lot of bait (usually 500) and using the fishing action once; your character should constantly cast your line back and forth. You just have to press the skill once for your character to automatically re-fish.

To begin fishing, you need to buy the Skill book from Common skills from a Skill Trainer. Then use a Skill point on the Fishing Skill. You should have Level 1 Fishing. Go to the Grocery Merchant and buy a Rod and Level 1 Bait (bread). Then go to your designated fishing spot, and press C, click Actions, then look for "fishing" and right click on it. You can fish near the Dock; you'll see many people fishing!

The higher your fishing level is, the better bait you need. When fishing, you can obtain Dissolution Pearls, herbs, dust, butterfly fish, junk items, armors, weapons, and accessories.

Note: Fishing can only be done in towns such as Roxbury. It is not yet possible to fish in other islands like Ron or the Sea of Bones dungeon.

Your fishing level can be upgraded at certain Land levels. It is upgraded just like any other skill, the required level is reached (every 7 levels; e.g. 8, 15 etc.) and then a skill point can be added to upgrade it. The next level of bait is then usable, so don't forget to buy it. The higher your fishing skill, the easier it is to catch fish, and the more likely it is that you will catch the butterfly fish as well.

[edit] Dissolution Pearls by Fishing Level

• Fishing / Bait level 1 - Grade 4, 5 Seal Break Pearls
• Fishing / Bait level 2 - Grade 3, 4, 5 Seal Break Pearls
• Fishing / Bait level 3 - Grade 2, 3, 4, 5 Seal Break Pearls
• Fishing / Bait level 4 - Grade 1, 2, 3, 4, 5 Seal Break Pearls
• Fishing / Bait level 5 - Grade 1, 2, 3, 4, 5 Seal Break Pearls