I read a very interesting article from Hakai Magazine regarding how fish feel pain. The audio to the article is down below. Check it out!
Neurobiologists have confirmed a long time ago that fish have nervous systems that respond to pain but generally speaking this fact is still ignored. When you are using your hooks the reel in fish, please remember that fish have more than 20 pain receptors their mouths and heads.
If you want to read the article go here: https://www.hakaimagazine.com/features/fish-feel-pain-now-what/