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