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.
Collect 150 coins.
Reach 300 points.
Buy all fishes in the game store
Buy whale
Collect 75 coins.
Buy Imperator fish
Reach 200 points.
Collect 25 coins.
Fall on a flying bird.
Buy Goldy fish
Obtain a coin and die a second later.
Get into the mouth of a shark.
Reach 100 points.