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