Despite popular belief that they don’t feel pain, fish still have nociceptors, which detect pain and physical contact, but it’s not been proven that they sense it the same way we do, through pain, as they lack the organs and organelles that interpret feeling into pain, they do however, respond to pain like we would expect from an animal that can feel pain, with muscle contractions and by pulling away in general, we’ve not tested every part of a fish nervous system that’s different to our own either, meaning that some part of it that is foreign to us could exist to interpret feeling into pain, it makes sense from an evolutionary stand point that they can feel pain too, however, there is a lack of evidence on both sides and much of the evidence contradicts other evidence, so only time will tell if we’ve been unnecessarily torturing fish for years.