Make money? I did monkfish.
But if you want to skip out on the money making and just grind until 90 (Rocktails are huge profit mine aswell)
Just power fly fish.
theres no fast way AND make money, best off fly fishing at barb village, dropping the fish, it's about 50-60k xp/hr, fastest xp to level up tbh, if you wanna make money, i'd say fish lobsters.
The fastest is C2 dung fishing which can get up to 120k/hr. The next fastest is low-alching barbarian rod fish which is around 85k xp/hr. The third fastest is mouse key dropping while fly fishing in Shilo or Barb at 75k/hr. Howeve, none of these profit at all. With profit you would be best to do monkfish, with about 45k xp/hr.
Alot of people didnt read the question and responded with just the FASTEST xp.. which is indeed fly fishing. He ASKED how could he also make money at it i suggest lobs at your level as they are pretty quick close to bank at FG. Monks are better for money but slower xp. GL getting to 90