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