Here is the full list of all 27 Aquaria achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Find all the recipes in the game.
Find all the Ancient Turtles.
Travel to all the areas of Aquaria.
Learn all the songs in Aquaria.
Rescue all the lost souls.
Discover two peculiar-looking fish...
Kill the Coward.
Ride Ekkrit for a minute.
Defeat Mom and Dad.
Find all the health eggs.
Enter the belly of the Whale.
Reach the Frozen Veil.
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Defeat the King Jelly.
Beat the Arnassi race in less than a minute.
Defeat the Rock Crab.
Defeat the Mantis Shrimp.
Defeat Octomun.
Dive into the water from a certain high location...
Fling a Monkey.
Devour a Parrot.
Reach the Veil.
Defeat Mergog
Defeat the Priests.
Devour 6 creatues in a row.
Reach the Sprite Cave.
Reach Open Waters.