Here is the full list of all 21 The Aquatic Adventure of the Last Human achievements worth 1,000 gamerscore.
First boss eliminated. Instantly mastered the uses of the harpoon.
You fully extinguished the human race...
Kill the Seahorses.
Kill the Zombie fish.
Kill the Tranquil
Kill the Anglerfish.
Kill the Hammerheads.
Kill the Parasite.
Kill the Lobster.
Kill the Bloodray.
Kill the Flower.
Complete the game.
Kill the Guardian
Read all holotapes.
Find all the upgrades.
Unlock hardcore mode.
Incapacitate the Tranquil.
Complete the Boss-rush Mode.
Complete the game without any upgrade crates.
Complete Hardcore mode.
Kill 100 Fish in one game.