I'm new to fishing, but pretty much got the jist of how things work. Basically, things can be a little confusing because unlike BTN/MIN gathering, you don't see the efficiency and HQ rates of the fish you target. However they are still there.

Your gathering rate will depend on your level and the level of the fish. Some fish have a minimum gathering requirement and if you don't meet it, not only will you not get HQ, you won't even get a chance at a bite.

HQ works off of perception. The higher it is, the more the percentage goes up. Since we can't see the number, it's safe to assume that a fish around your level will be low even with Max stats for your level, so it's all about the generosity of RNGesus. You have to patient with fishing or you just won't cut it.

Speaking of patience, you do get abilities 50+ that help with HQ catches and they cost GP to use. So plan on having plenty of cordials on hand if you continue to go after HQ fishies!