Whether and how animals perceive pain remains a subject of debate in scientific discourse. After all, we cannot simply ask the animals. However, anyone who has ever seen a fish fight for its life, whether while angling or in a documentary, may have concluded that this creature is at least reacting to the danger to which it is exposed. And that is precisely the biological function of pain: evolution has produced a mechanism that not only signals danger to sentient beings, but also involuntarily drives us to escape it. A survival strategy.
It took a long time for science to gather concrete evidence of this. Finally, in 2002, receptors responsible for the perception of pain were identified in fish. In addition, there are those that can suppress pain, for example when activated by adrenaline. We are familiar with this phenomenon ourselves: when we are in shock, pain is initially secondary until we are able to calm down. Thus, fish possess a nervous system complex enough to perceive and react to pain.
Yet, to this day, the claim that fish cannot feel pain persists. Perhaps it endures because it helps us accept that every year, millions of tonnes of fish worldwide end up in nets and die a slow death. After all, denial is also a viable survival strategy.
Source: L.U. Sneddon (2015): Pain in aquatic animals. The Journal of Experimental Biology. https://doi.org/10.1242/jeb.088823
