Fishing to level 20. My Experience.

[Terran]

Just add perks and level ups and stuff. A stat screen or something.

Fishing Speed
Catch Rarity
Casting Rate
Special Chance
Lure Extender

blah blah. Then have cool perks. Do it like Stardew Valley. I.E:

1%/2%/3%/4%/PERK1+5%/6%/7%/8%/9%/PERK2+10%

perks like, 1 in x chance to double a fishes' weight, 1 in x chance to not use a lure up, auto type the first letter or two, etc.