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