“…the way humans readily project their emotions and intentions into some animals and not others is itself a cause for concern. Few people have much fellow feeling for fish even though many fish are long-lived, have complicated nervous systems and are capable of learning complicated tasks.”
—Professor Patrick Bateson
Professor of Ethology University of Cambridge
From salmon making the long journey from river to ocean and back, to goldfish swimming circles around a small pond, the inner lives of fishes are a mystery that scientists are only beginning to unravel. One of the key elements they are searching for is the extent to which each fish is sentient or, more specifically, how they process what we would call a “painful” sensation (such as a hook cutting into their lip.)
On this journey, scientists have discovered that fish have nerve structures that are anatomically very similar to those of humans and many other species of animals. Among these common structures are receptor cells called nociceptors, which are found throughout animals’ bodies and are activated by stimuli expected to cause damage to bodily tissues. Tellingly, some species of fish have upwards of 58 different nociceptors located in their lips alone*.
As in human anatomy, these nociceptors are wired by nerve fibers to the central nervous system (the spinal cord and brain.) When the pain centers in the brain are activated by signals from the nociceptors, they trigger the body to respond to the potentially harmful or life threatening events that may be happening.
Fish anatomy is so complex that they have even evolved the same “pain-blocking” substances (endorphins) as humans.** It is theorized that endorphins help animals to tolerate pain from severe injuries in order to help them escape from a predator. This leaves us with the question: Why would fish have endorphins in their bodies if they couldn’t feel pain? And why is there still a debate over their sentience?
* Physiologist Lynne Sneddon discovered 58 different nociceptor sites in rainbow trout lips.
** Endorphins are akin to naturally occurring morphine, although their role in the body is more complex. It is also worth mentioning that some analgesic drugs used by humans also appear to reduce pain in fish.
Next: Do fish feel pain in the same way we do?