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