Here is the full list of all 13 Nimble Fish achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Get into the mouth of a shark.
Fall on a flying bird.
Obtain a coin and die a second later.
Reach 100 points.
Reach 200 points.
Reach 300 points.
Collect 25 coins.
Collect 75 coins.
Collect 150 coins.
Buy Goldy fish
Buy Imperator fish
Buy whale
Buy all fishes in the game store