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