have nociceptors, that’s true, but the reason I believe their experience of “pain” is nothing like the human experience is the difference of their brains.

The horror of pain in humans is the psychological effect of pain. The way the signal from the brain is interpreted or “understood” in the brain. In humans the very same signal from “pain” nerves can be interpreted as pleasurable by the brain. This can actually be changed in humans. This is probably also true to varying degrees in some other mammals etc, but I don’t believe a fish’s experience of pain is anything like the psychological effect that we relate to and project onto them. They simply don’t have sufficient development of the brain structures that do that in higher-order brains.

They can have reactions toward the detection of stimuli and they can even develop learned reactions or change behavior based on receptions from nociceptors. That’s an important evolutionary adaptation toward survival. But it doesn’t prove that their experience of pain is anything like ours.

I would be more willing to call what a fish experiences “panic” but even that is probably too strong a word. We trigger the sympathetic response, as they have it, and their instinct to “Flight” is set off by their nociceptors and limited brain response.

I’ve seen fish in heavily-fished C&R rivers (like the San Juan in New Mexico) develop a process that has largely moved past the panic response. They are used to it. They may even have a broken-off hook already left in their mouths but will go immediately back to feeding apparently comfortably. Will even move directly behind a fisherman whom they use as a current break. Will continue to feed as though nothing has happened.
I even once caught a 26 inch rainbow on 6x tippet (extremely small line) and a size 26 fly which shouldn’t have been possible except that I chose to loosen the line so it thought it had broken another angler off and immediately settled on the stream bed so I could sneak up behind it, tighten the line and lift it up to net it. It was just following a learned behavior and cared almost nothing about the hook still in its mouth.

Not torture. Not even pain as we understand it.

You don’t have to feel badly.