The Brain Structure of Fish – Can they feel Pain?

”I only eat fish.”Why do you have a video with fish?” These are popular phrases from pedestrians on “Cube of Truth” Events. At those events, some activists show films of different animal industries on screens, and other activists talk to the pedestrians who had been watching these films for a bit. (Pic. 1). Module two covered the different brain structures of humans and animals. The assumption of why it is better to eat fish than other animals often comes from the point of view that fish cannot feel pain and do not have a mind because of their different brain structure. This seminar takes a more in-depth look into the construction of a fish brain, explains where the idea of the inability to feel pain comes from, and presents scientific studies about this issue.

Picture 1: Me showing a film about fish 07/2018.

Definition

Pain is a warning signal of the body. It alerts the brain because of an inner issue or an influencing outside stimulus that could cause damage to the body. There is no pain center in the cortex, but there are discreet parts in the brain stem where pain signals of the peripheral nervous system arrive. Pain is a signal for danger (Hickman et al. 2008).​

The Brain

Figure 1 shows the brain structures of a fish and a human being. The neocortex is a late evolutionary development of the vertebrate evolution. There is a motor cortex and a sensory cortex. The sensory cortex is the center for the mindful awareness of stimuli like pressure, touch, taste, temperature, and pain (Hickman et al. 2008). Because there is no neocortex in the brain of a fish (Fig. 1), there are meaningful discussions about the question if fish can feel pain, which led to the subsequent studies. Birds and amphibians also lack a neocortex (Stevens, Gentle 1992).

Figure 1: Fish brain and Human brain (fishpain.com).

Scientific Studies

Lynne Sneddon (2011) researched fish pain at the University of Liverpool. She poured one chamber with a painkiller and another chamber with regular water. The zebrafish were in a maze, where they could choose one of the two chambers. The chamber with the sedative was barren, the one with regular water was enriched with gravel and a plant, and due to the transparent rear of the chamber, a group of other zebrafish was visible and provided social enrichment. Under normal conditions, the fish chose the enriched chamber for at least six consecutive days. Then the scientist injected the zebrafish with saline, a non-noxious control, or a harmful chemical, and placed them in the maze. The fish who were experiencing pain lost their preference for the enriched chamber and spent more time in the barrel chamber.

Chervova and Lapshin (2004) tested the sensitivity of pain in cod, rainbow trout, carp, and sturgeon. In their experiment, they applied painful bursts of electricity to the tail fins and got a moving tail fin as a response. They used an optical-mechanical system to record the response to painful electrical stimulation. After they collected the data, they gave the fish painkillers and repeated the shocks. The pain sensitivity was reduced by up to 89 percent.

In Ireland, a study was made by Dunlop and Laming (2005). They picked up a goldfish with a pin and recorded the parts of the fish that responded to this painful event. Heat and pressure were also used to get pain responses. To these actions, the scientist recorded nerve responses from the spinal cord, cerebellum, midbrain, and forebrain. “The perfect setting of timed prods allowed the latency of the response to be calculated in all regions. From this data, conduction velocities suggested that A-delta and C fibers were activated.” These fiber groups are also known to be used in pain transmission in humans. Because of these results, scientists understood “that there is neuronal activity in all brain areas, including the telencephalon, suggesting a nociceptive pathway from the periphery to the higher central nervous system of fish.’’

Discussion

Even though there are a lot of studies about pain fish experience, there are still people who argue that these studies do not prove the ability to feel pain. “There is no survey method which unequivocally distinguishes between pain and unconscious stimulus processing. It is pure speculation that there is a different brain region responsible for the sensation of pain in fish,” argues Robert Arlinghaus, a professor at Humboldt-University in Berlin (Süddeutsche Zeitung 2015).

What happens to a fish once it’s out of water? Because of decompression, the swim bladder tends to tear; the stomach bulges out of the mouth, and the eyes bulge as well (Pic. 2). (Eichelsheim 2015). Most of the fish suffocate when taken out of water because their gill arches collapse. This process to their death can take hours, and sometimes they are still alive when they are sliced and gutted or placed on ice (Neslen 2018).

The study Lynee Sneddon conducted shows that fish were willing to pay the cost of being in an unpreferred environment to obtain a painkiller. This indicates that the fish got some reward for this behavior, such as, maybe, pain relief, which means that they are capable of feeling some pain.

Picture 2: Eyes pop out of the head (Eichelsheim 2015).

Conclusion

The studies I have cited, prove that fish can experience pain and that practices like fishing impair the welfare of fish. Also, it shows that fish can learn and change their behavior if the circumstances of their environment are changing. From a physiological point of view, fish have nociceptors, which are pain-sensing nerves, and a central nervous system (Jaeggi 2017). Fish are living in a completely different environment. It seems pretty simple to argue that just because they do not have the same sophisticated brain structure as humans, they cannot feel pain.

Commercial fishing kills 970-2.700 billons fish each year (Mood & Brook 2010). Also, 37-120 billion fish get killed in aquaculture production (Mood & Brook 2012). With these high numbers and the brutal way in which most of these fish are dying (see discussion) it should be very alarming if these non-human animals are capable of feeling.

I would argue that as long as it is not 100 percent distinct that they do not feel pain, it should be forbidden to treat them the way it is common these days. Rather than argue from the point that it is acceptable to harm them in this way just because we do not know if they feel pain.

Word count: 1098 words

References

Chervova, L.S. and Lapshin, D.N. (2004). Pain sensitivity of fishes and analgesia induced by opioid and nonopioid agents. Proceedings of The Fourth International Iran & Russia Conference, 1420-1425.

Dunlop, R. and Laming, P. (2005). Mechanoreceptive and nociceptive responses in the central nervous system of goldfish (Carassius auratus) and trout (Oncorhynchus mykiss).The Journal of Pain.6 (9), 561-568.

Eichelsheim, J. (2015). How to release fish caught in deep water. 07 Dec. Available at: https://www.stuff.co.nz/sport/boating/74819080/how-to-release-fish-caught-in-deep-water[accessed: 11 Nov. 2018].

Gentle, M.J. (1992). Pain in birds. Animal Welfare. 1, 235-247.

Hickman, C.P., Roberts, L.S., Larson, A., I’Anson, H. and Eisenhour, D.J. (2008). Zoologie. München. Bayern. Deutschland. Pearson.

Jaegi, P. (2017). Auch Fische haben Schmerzen. 04 May. Available at: https://www.swr.de/swr2/wissen/fische-empfinden-schmerzen/-/id=661224/did=19481312/nid=661224/1sd49il/index.html[accessed: 09 Nov. 2018].

Mood, A. and Brooke, P. (2010). Estimating the number of fish caught in global fishing each year. Jul.Available at: http://fishcount.org.uk/published/std/fishcountstudy.pdf[accessed: 09 Nov. 2018].

Mood, A. and Brooke, P. (2012). Estimating the number of farmed fish killed in global aquaculture each year. Jul. Available at: http://fishcount.org.uk/published/std/fishcountstudy2.pdf[accessed: 09 Nov. 2018].

Neslen, A. (2018). 'Horrific' footage reveals fish suffocating to death on industrial farms in Italy. 18 Oct. Available at: https://www.theguardian.com/environment/2018/oct/18/horrific-footage-reveals-fish-suffocating-to-death-on-industrial-farms-in-italy[accessed: 11 Nov. 2018].

Seddon, L.U. (2011). Pain perception in fish: Evidence and implications for the use of fish.Journal of Consciousness Studies. 18 (9-10), 209-229.

Stevens, C.W. (1992). Alternatives to the use of mammals for pain research. Life Science. 50, 901-912.

Süddeutsche Zeitung. (2015). Können Fische Schmerzen empfinden? 04 Jun. Available at: https://www.sueddeutsche.de/leben/angeln-und-moral-vom-toeten-und-geniessen-1.2480152-2[accessed: 09 Nov. 2018].