Is it with poles or with baits?
#How to get better fish? (bronze, silver, etc.)
foggy hemlock
astral spindle
Clean up the ocean. They tied quality with diving so the more orbs you activate the more chance you have of getting better quality of fish.
I’m not sure if they tied it to poles too. I have noticed that I’m getting more gold and purple fish since I got the master pole, but that could be coincidence. I’ve gone as far as I can in diving and I’m level 6 in fishing.