In Abyss, certain quest items are far rarer and more confusing to obtain than standard fish, and Fish Bone is one of them. If you are progressing through Ancient Sands, you will eventually run into quests from both Marcus and Grumpy Hank that require this item. So, to help you, this complete guide explains exactly how to obtain Fish Bone, how the mini-game works, and where it is used so you can progress through the game easily.
Where to Find Fish Bone in Abyss

Fish Bone can only be obtained while fishing in Ancient Sands in Abyss. The process is identical to catching Geodes elsewhere in the game, with one important difference. When fishing in Ancient Sands, the Geode reward is sometimes replaced with a Fish Bone instead.
How Often Does Fish Bone Spawn?
While fishing, a Treasure Chest icon can appear on the mini-game bar alongside the standard fish progress bar, so there isn't any clear indicator whether you are going to get a Geode or a Fish Bone. This happens roughly once every five fishing attempts (20%). When the Treasure Chest icon appears, you need to fill its internal bar before finishing the main progress bar. If you complete the fishing mini-game without filling the Treasure Chest bar, you will not receive the additional reward.
To maximize your chances, first fill the main fishing bar to around 75% percent. Then shift your focus to the Treasure Chest bar until you see a check mark. Once that is done, return to the main bar and finish the mini-game. I suggest going for Cods or Pompanos, since their mini-game bar usually isn't erratic. This makes it easier to complete rather than having to scramble up and down (especially considering that the Chest icon always stays in one place).
Related: Roblox Abyss Artifacts Tier List
How to Use Fish Bone in Abyss

Fish Bone is primarily used as a quest item for NPCs Ancient Sands. Considering the more quests you complete, the more Fish Bones they will ask for, just make sure to always go for the Chests when you see them. As suggested above, if you want to farm Fish Bones in Abyss, try to catch Cods and Pompanos. There are always plenty of them near Crazy Jeff's Shop so this makes it evn easier.
Frequently Asked Questions (FAQs)
Fish Bone can only be obtained while fishing in the Ancient Sands region through the Treasure Chest mini-game.
No. The chest mini-game guarantees a special reward, but in Ancient Sands it can be either a Cactus Geode or a Fish Bone.
No. Fish Bone is a quest-specific item and cannot be sold, traded, or used outside NPC questlines at the moment.
Now that you know how to get Fish Bone in Abyss, check out All Fish in Spirit Roots or All Fish in Ancient Sands, here on Pro Game Guides.