Are Fish Capable of Feeling Pain?

The simple answer is yes. Many scientific studies over many years have demonstrated that fish feel pain. To be precise, this doesn’t just mean that fish physically react to potentially injurious stimuli, but rather, that they actually experience a sensation of pain.

In a study conducted by the University of Liverpool, zebrafish were given a choice of two tanks: One was barren, while the other was enriched with pleasant views of other fish and foliage. Initially, the zebrafish chose to be in the enriched tank. However, some of the fish were then injected with acid, while the barren tank was pumped full of painkillers. The fish who’d been injected with acid moved to the tank with the painkillers.

A  similar study, conducted by Sneddon in 2002, sought to test fishes’ psychological states, not just their physical reactions, when exposed to pain. This time, the subjects were rainbow trout.

First, Lego blocks were dropped into their tank; under normal circumstances, a trout will avoid an unfamiliar object in its presence. But the trout in this study were injected with acid, and once they were, they stopped trying to avoid the Legos — presumably, because they were distracted by their own pain. Meanwhile, a second group of trout was injected with acid and then morphine, a powerful painkiller. The trout who received the acid and the morphine behaved as they normally would have (that is, by avoiding the Legos).