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