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