Here is the full list of all 27 Aquaria achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Kill the Coward.
Beat the Arnassi race in less than a minute.
Find all the recipes in the game.
Travel to all the areas of Aquaria.
Discover two peculiar-looking fish...
Find all the Ancient Turtles.
Learn all the songs in Aquaria.
Rescue all the lost souls.
Find all the health eggs.
Reach the Frozen Veil.
Defeat the King Jelly.
Enter the belly of the Whale.
Defeat Octomun.
Fling a Monkey.
Devour a Parrot.
Dive into the water from a certain high location...
Defeat the Priests.
Defeat Mom and Dad.
Defeat Mergog
Reach the Sprite Cave.
???
Reach the Veil.
Defeat the Rock Crab.
Defeat the Mantis Shrimp.
Ride Ekkrit for a minute.
Devour 6 creatues in a row.
Reach Open Waters.