I think it arises from the genetic traits in all fish. The genetic traits are hard wired for control/prominence differently at different times. One of those is the stress indicator chemical noted above . At different times , reproduction comes first , at other times feeding , the flight (safety) response at other times, aggressiveness , caution , and on. When conditions are right for feeding (low stress) and all of the sudden one fish is hooked ,dragged around , lifted out of the water and put back in ,during that process it releases a stress indicator (warning signal) the others pick up on. They react when the signal is strong enough and it overrides the feeding signal and they stop feeding for a while. Same for spawning priority overriding the stress chemical during the BG spawn. Spawning ranks higher at that time and you can catch a bunch off the beds. But if you let them see you then the flight response is greater and they will move off the nests for protection. Because of genetic variation between different species and between different individual fish in a population of one specie you get different levels of traits and thus different results.