Here is the full list of all 21 Pacifish achievements. It takes around 80-100 hours to unlock all of the achievements on Windows.
Find all five shells
Use 1000 bait
Reach Swimmer level 10
Find the Black Orb
Acquire Sam's journal
Complete 50 thousand catches
Earn 500 million coins
Earn 50 million pixels
Eat 10 million fish
Hatch 10 million fish
Reach Fisher level 100
Defeat 50 thousand enemies
Reach fight area 100
Defeat all bosses
Reach Market level 50
Spin reels 50 thousand times
Get 1000 matches
Unlock Dam and Sky fishing
Own all fishing poles
Own all tackle
Craft 20 fishing pole mods