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