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