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