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