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