As already mentioned there are a few buffs, consumables, baits, tackles and so on.
With the mastery points it is no problem to maintain fishing power over 500 and possibly up to 900+.
I reccommend this guide as it was quite a work to get the information and is the best overview i saw.
https://www.reddit.com/r/Guildwars2/comments/t7qc8h/end_of_dragons_fishing_sheet_kinda_spoilers/