Anyone who has ever gone fishing has likely wondered if the fish they catch feel the pain of the hook that catches them. Whether or not fish feel pain has been a hotly debated topic for decades, and for good reason. Since fish aren’t mammals, they don’t show many of the signs we associate with pain. Fish don’t grimace, yelp, or cry, and they flop around with handling, so it’s hard to know if they’re responding to pain, reflex, or instinct. If you’ve ever wondered if fish feel pain, here’s what you need to know.divider1- goldfish

Do Fish Feel Pain?

Yes!

Fish absolutely feel pain. How do we know this? Well, fish have specific neurons in their bodies that are called nociceptors. Nociceptors are responsible for detecting potentially harmful stimuli, like extreme temperatures, chemicals that may cause burns or injury, and other dangerous things. Think of it this way: if you were squeezing a fish and started increasing pressure as you squeezed, the fish’s nociceptors would kick into action and immediately tell the fish’s brain that something’s wrong, causing the fish to reflexively respond and try to escape.

When stimulated, nociceptors send electrical impulses to the brain that tell the fish to react. We all know that brains are made up of multiple parts, and fish brains aren’t an exception to that. Fish do have a brainstem and other parts of the brain that are associated with reflex and impulse. This is the part of the human brain that tells you to take your hand off the hot stove before you may consciously realize it’s hot.

However, fish also have a cerebellum, which is responsible for non-reflexive motor skills, and a telencephalon, which is also known as the forebrain. This is where the parts of the brain associated with learning, memory, and behavior are located. In fact, if you look at a diagram of a fish’s brain versus a mammal’s brain, they have a lot of similarities, and we know that fish produce naturally occurring opioids for pain control, just like people and other mammals do.

goldfish-in-aquarium_antoni-halim_shutterstock

Credit: antoni halim, Shutterstock

How Do We Know That Fish Feel Pain?

Scientists have performed multiple studies on different types of fish to determine if they do feel pain. This can be difficult since they can’t tell us if they’re in pain. Unfortunately, this means that testing the theory of fish feeling pain involves producing painful stimuli in fish.

One study involved monitoring the brain activity of goldfish and rainbow trout before, during, and after having a small pin stuck into the soft area behind their gills. When pricked, these fish’s brains showed the nociceptors sent notifications of pain to both the unconscious parts of the brain, like the brainstem, and the conscious parts of the brain, like the cerebellum.

Another study involved rainbow trout, which are naturally cautious fish. In this study, the fish were monitored while colorful blocks were dropped into their tank. Due to their natural overabundance of caution, the fish avoided the blocks. However, fish that were injected with acetic acid, which caused pain, were less likely to respond to or avoid the blocks when they were dropped into the tank. This insinuates that the experience of being in pain was a distracting experience for the fish, preventing them from exhibiting their normal level of caution. Fish that were injected with acetic acid and morphine, though, were once again cautious around the blocks. The insinuation of this behavior is that the morphine dulled the pain from the acetic acid, no longer distracting the fish from their normal responsive behavior, which shows that this avoidance behavior is only partially driven by instinct and reflex.

A study involving zebrafish also elicited some interesting responses from the fish. In the study, the fish were given the option between two tanks. One tank was empty, containing nothing but water, while the other contained greenery, gravel, and a view of fish in other tanks. When given the choice, the zebrafish consistently chose the more interesting tank. After this experiment, the zebrafish were injected with acetic acid, causing pain. The empty tank had lidocaine, which is a pain reliever, dissolved in the water while the more interesting tank did not. In this experiment, the zebrafish consistently chose the tank with the painkiller. Then, the zebrafish were injected with acetic acid and lidocaine, so they were uncomfortable but had pain relief in their bodies. In this instance, the fish began once again choosing the more interesting tank.

What Kind of Pain Do Fish Feel?

Here’s where things get tricky because we actually don’t know the answer to this. We can monitor brain activity and behavioral responses all day long, but what we can’t do is understand the subjective experience of other living things. Fish do have less developed brains than humans and other mammals, so it’s possible that they experience pain but not in the same way that we do. This could be related to the way their brains work or it could be related to their understanding of painful stimuli. At this point, science hasn’t been able to tell us which one it’s related to, though.

Then again, we see a lack of understanding of pain even in our mammalian friends. When your dog or cat are in pain, they often are very confused about it. With people, we are able to understand concepts like getting a shot being worth the pain to prevent an illness, but our pets just know that they are uncomfortable or in pain in that moment. Even if fish have a higher level of sentience than we realize, they still likely have confusion about pain.

In Conclusion

Fully understanding how fish feel pain is a long way off, but science has made great advances that have shown us that fish do, in fact, feel pain. Treating our scaled friends gently and with kindness is the best thing we can do for them. Many fish show behaviors that indicate they understand concepts like recognition and memory, so it’s certainly possible that treating your fish with kindness will build up a level of trust and provide them with a happier, more secure life.


Featured image credit: Nature and Life, Shutterstock