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.
Beat the Arnassi race in less than a minute.
Travel to all the areas of Aquaria.
Find all the Ancient Turtles.
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.
Defeat Mergog
Enter the belly of the Whale.
Reach the Frozen Veil.
Defeat the Rock Crab.
Defeat the Mantis Shrimp.
Defeat Octomun.
Dive into the water from a certain high location...
Devour a Parrot.
???
Fling a Monkey.
Reach the Veil.
Defeat the Priests.
Devour 6 creatues in a row.
Ride Ekkrit for a minute.
Reach the Sprite Cave.
Kill the Coward.
Reach Open Waters.