Do fish feel pain?
According to scientific studies, fish have pain receptors and the stimuli are transmitted to the brain. A potential pain stimulus activates areas in the brain of the fish that most likely perform the same task for the fish’s perception as the areas of conscious pain perception in more highly developed vertebrates. In addition, behavioral patterns and decisions of fish – for example, the learned avoidance of situations associated with injury – indicate a conscious perception of pain.
More information (available in German only) can be found here: https://www.aquakulturinfo.de/schmerzempfindung-bei-fischen