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