That trout's nociceptors are probably firing like crazy. Guy Crittenden/ Getty Images

We know that pain is uncomfortable, but what exactly is going on in our bodies that causes us to wince and tear up? According to the International Association for the Study of Pain, pain is a twofold experience. First, you have the neurobio­logical process of our nerves communicating with the brain. Second, there's the emotional response to pain that varies from person to person. (For more details, you can read about humans' pain response in How Pain Works.)

Despite its bad reputation, pain can be a handy survival tool. Think about the sensory reaction of putting your hand on a hot stove, registering the burn and retracting your arm. In this way, pain protects us. It tells your body that you're in danger of tissue damage and need to get to safety. Nociceptor nerve cells in our bodies deliver that initial pain-related communiqué along a route through the central nervous system to the brain. Research has shown that other mammals, birds and fish also have nociceptors. The presence of those nerve cells implies that fish have the sensory capability to recognize when something is harming their bodies. Hence, fish can experience the neurological pain process.



One of the primary arguments against fish having a sense of pain is that their brains lack the structural elements, namely the neocortex, necessary for it. Although fish's brains are certainly less complex than ours, they aren't mindlessly floating around in the water. Akin to the fight-or-flight response, fish have chemicals in their bodies that are released when they're in danger [source: Chandroo, Duncan and Moccia]. Fish also possess pain nerve fiber tracts in their bodies that are similar to those that tetrapods (vertebrates with four limbs) have [source: Chandroo, Duncan and Moccia]. Overall, the scientific consensus is that fish have the anatomical requirements to demonstrate neurophysiologic and behavioral reactions to pain as a means of survival [source: Braithwaite and Huntingford].

However, little evidence exists to suggest that the fish also react emotionally to pain like humans. As another way of safeguarding our bodies, our pain response comes with a negative emotional reaction that excites the amygdala in our brains and forms a memory of the unpleasant effect of a particular stimulus. For that reason, most children will touch a hot stove only once. Fish brains do contain an amygdaloid complex, but it produces aggression rather than fear [source: Chandroo, Duncan and Moccia]. Nevertheless, fish are able to form sensory memories. For instance, trout can remember how to avoid getting caught in fishing nets months after the initial experience [source: Donkin]. So while it remains unclear whether fish genuinely suffer from pain, memories of it stick in their brains.

If fish can sense pain but don't necessarily feel it emotionally like humans, where does that leave us? The fishing industry has already instituted catch-and-release policies to reduce the number of purposeless fish deaths. Some fishermen use barbless hooks and necks that cut down a fish's struggle time before being reeled in. As for the lobster, chefs may kill them by striking them swiftly through the eyes rather than dropping them into the boiling water alive [source: Wallace].

Ether way, it's morally debatable. For some people, no amount of concrete proof of a fish's agony could tear them away from hooking a fresh bass or trout. To others, people who fish are detestable because they inflict pain onto another living being. Whichever side of the line you stand on, there's one thing easily agreed on: Whether fish, fowl or mammal, neurological pain happens to us all. It's the capacity for suffering that remains up for dispute.