Fish Bone is a rare quest item in Abyss that appears exclusively while fishing in the Ancient Sands region. You need nine total to complete Marcus the Archaeologist's full questline, which rewards money, oxygen upgrades, potions, keys, and geodes. The item cannot be sold or traded—it exists only for these specific quests.
Quick answer: Fish in Ancient Sands until a Treasure Chest icon appears on the fishing mini-game bar, fill the chest's internal bar to 100 percent before finishing the main progress bar, and you'll receive either a Cactus Geode or a Fish Bone.
Fishing for Fish Bone in Ancient Sands
Fish Bone drops from the same treasure-chest mechanic used to obtain Geodes elsewhere in Abyss. While fishing in Ancient Sands, a small Treasure Chest icon occasionally appears on the right side of your screen alongside the standard fish progress bar. This happens roughly once every five fishing attempts—a 20 percent spawn rate.
When the chest icon appears, you must fill its dedicated progress bar completely before you finish catching the fish. If you complete the main fishing bar without filling the chest bar, you forfeit the bonus reward. The chest bar fills as you keep your reticle aligned with the moving fish icon, just like the main bar.
Step 1: Cast your harpoon at any fish in Ancient Sands and wait for the Treasure Chest icon to appear on the mini-game bar. If it doesn't show up, finish the catch normally and try again.
Step 2: Fill the main fishing progress bar to around 75 percent, then shift your focus entirely to the Treasure Chest bar. Keep your reticle on the fish icon until a checkmark appears over the chest.
Step 3: Return to the main progress bar and finish the catch. The game will award either a Cactus Geode or a Fish Bone when the chest bar was completed.
The drop is not guaranteed—Ancient Sands chests can still yield Cactus Geodes instead of Fish Bone. You'll need to repeat the process multiple times to collect all nine pieces.
Marcus's Questline Requirements
Marcus the Archaeologist stands in Ancient Sands and offers three quests that require Fish Bone at different stages. Each quest unlocks after you complete the previous one, and the rewards scale up with each tier.
| Quest Name | Fish Bones Required | Rewards |
|---|---|---|
| Deeper Analysis | 1 | $1,600, Star Shards, Small Oxygen Pods |
| Shifting Evidence | 2 | $3,850, Speed Potion, Basic Oxygen Pods |
| Beyond My Reach | 6 | $7,800, XP Potion, Cactus Geodes, Burger |
The final quest, Beyond My Reach, requires six Fish Bones at once, so you'll want to stockpile them before turning in the earlier quests. Completing all three quests also grants you an Ancient Sands Key, which unlocks a Fish Shrine in the same region for additional loot.
Verifying Successful Chest Completion
You know the chest mechanic worked when a checkmark icon appears over the Treasure Chest symbol before you finish the main fishing bar. If you complete the catch and receive only a standard fish with no bonus item, the chest bar was not filled in time.
The game does not display a separate confirmation message for Fish Bone versus Cactus Geode drops—you'll see the item appear in your inventory immediately after the catch animation finishes. Check your hotbar or inventory screen to confirm which reward you received.
Common Chest Mechanic Failures
The most frequent mistake is finishing the main progress bar too quickly. If you fill the fish bar to 100 percent before the chest bar reaches full, the bonus reward is lost. Always prioritize the chest bar once it appears, even if it means letting the main bar sit at 75–80 percent for several seconds.
Another issue occurs when players lose track of the moving fish icon while focusing on the chest. The chest bar only fills when your reticle stays aligned with the fish, so you must maintain accuracy on both bars simultaneously. If the fish icon drifts too far from your reticle, both bars will pause or regress.
Finally, the Treasure Chest icon does not appear on every cast. If you fish five times in a row without seeing it, that's normal variance—the 20 percent spawn rate means streaks of bad luck are common. Keep fishing in Ancient Sands until the icon shows up.
