The Economy & Museum
Making money, dynamic prices, and preserving history.
Currencies
Bubble Coins (earned from fishing/selling. The everyday spending currency), Bubble Gems (a scarcer, premium currency from dailies, golden fish, treasure and certain enchants. Used for backpacks, eggs, and guild expansion), and Ancient Museum Coins (earned exclusively by donating to the Museum, spent exclusively in the Museum Shop and on Minions).
Dynamic Selling Prices
Sell prices aren't fixed. Every sale nudges that specific species' local price down by about 1.5%, so dumping the same fish over and over gets you steadily less per fish. Down to a floor of 40% of its base price. Prices drift back up about 1% every hour, and can rise as high as 250% of base if a species goes unsold for a while. Selling a wide variety, or spacing out big sell-offs, keeps your average price higher.
Selling
Sell your catch to the game with /sell at that species' current dynamic price. There's no player-to-player market yet. See the Player Trading article for details.
The Museum
Once you've caught a species, donate it with /museum donate for a one-time reward of Ancient Museum Coins. Better/rarer fish are worth more. Artifacts (found from treasure and lockboxes) can be donated too, for their own Ancient Coin value. Each species can only be donated once, so the Museum is really a long, finite dex-completion grind rather than a repeatable income source.
The Museum Shop
Spend Ancient Museum Coins at /museumshop (alias .mshop) on permanent upgrades: small stacking boosts to Luck, coin bonus from selling, and treasure-chest chance; one-time unlocks like extra equipped-pet slots; and, at the higher end, all three Minions. It's the primary long-term sink for Ancient Coins once you've grabbed the basics.