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