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