Do fish feel pain?


As the ethical practice of rearing mammals and poultry for human consumption remains a subject of great controversy, turning to a pescetarian diet has for many, negated any concerns over animal welfare issues in the agricultural industry. The benefits behind such a diet are numerous, with seafood existing as a major source of protein and long-chain omega-3 fats, as well as being rich in other fundamental nutrients such as selenium and vitamin D. In particular, these omega-3 fats have proven to protect the heart against the development of erratic and potentially deadly cardiac rhythm disturbances (1) , leading to recommendations such as those by the Committee on Medical Aspects of Food Policy (COMA), to eat at least two portions of fish weekly.

In an age where 435 people will lose their lives from cardiovascular disease in a single day (2), seafood has become an important dietary component for many people wishing for a healthier style of living. Certainly there seems to be no downside to this mindset, if the creature itself cannot comprehend its life of containment, or feel the pain of capture, then where is the harm?  

The belief that fish cannot feel pain however is currently greatly contested within the scientific community. For many, the conclusion that fish cannot feel pain has originated from the fact that their brains are fundamentally different from our own. Not only do these organisms lack the neocortex (a neuroanatomical structure which allows for mammalian pain identification), but also the sensory neurons or nociceptors, that react to bodily damage are believed to be rare, or even completely absent across the taxon.

Though not the first study to introduce such an idea, Rose et al. (2002) remains one of the most prominent advocates against pain comprehension in fish(3). In his study, Rose argues that the normal behavioural responses of fish recorded shortly after intensive surgery, combined  with a lack of  c-fiber nociceptors in teleosts and elasmobranchs, are conducive to assume that these creatures do not have the ability to experience an anthropocentric sense of ‘pain’.  Any avoidance and escape responses exhibited from noxious stimuli were therefore considered to be merely reflexive, akin to how, without conscious thought, the human knee will perform an automatic jerk when tapped.

Since the study’s year of release in 2002 however, the paper has come under fire from a variety of different research scientists, revealing fundamental flaws in Rose’s reasoning.

The neocortex is a structure unique to higher order mammals. In assuming that pain sentience is purely determined by  a large, and considerably developed neocortex, Rose’s theory would thereby eliminate birds, amphibians, other non-mammalian animals, and even some mammals from having the capacity of feeling pain (4), rendering the theory completely unfounded.

Furthermore, pain is an indisputably important part of survival. It is an adaption that signals to an animal the damaging nature of a situation, thereby allowing them to remove themselves from this danger and survive, increasing the chances of that individual passing on their genetic information to future generations. As such, a crucial trait like pain perception is unlikely to suddenly disappear for one particular taxonomic class (5).  Zoological scientists have therefore argued that  rather than the pain system being viewed as a recent adaption in higher mammals, it should consequently be considered an old evolutionary trait (6) .  ‘All emotions, including the negative emotional experience of pain, may originate from the most phylogenetically ancient part of the brain—which is reptilian—indicating fish should also have the ability to feel pain. Pain perception in fish makes Darwinian and biological sense’ (5 Yue,  2008, pg. 2).

Through the utilisation of  functional magnetic resonance imaging (fMRI), Sneddon et al. (2006), demonstrated activation of the midbrain and forebrain of common carp during noxious stimulation (7). Had this response to potentially painful stimulation been merely reflexive, these cortical areas, let alone any section of the carp’s brain, would not have been activated.

Further study into the psychological aspects of fish pain perception has revealed that rainbow trout which were subject to noxious stimulation showed a dramatic rise in respiration rate,  (8) a response also seen in mammals enduring painful events. Carp and Zebrafish have also been recorded to display abnormal behaviours over a prolonged period of time (between 3-6 hours),  as well as their normal feeding behaviours halting until all adverse behavioural and physiological effects subsided. Upon the administration of morphine however, abnormal behavioural and physiological responses were ameliorated, demonstrating that these were pain related responses (9).

When confronted with the ample behavioral, neurobiological and physiological evidence regarding this subject, it is difficult to deny the fact that fish are capable of suffering from pain. Not only do they possess similar brain structures to those that are essential in mammalian pain identification, (i.e. the pons, medulla, reticular formation, locus coeruleus, periaqueductal grey, the thalamus and cortex), fish also show adverse behavioural and physiological responses to painful stimuli, to the extent that they are no longer able to exhibit normal behaviours.  

In light of such research demonstrating the capacity of fish to experience not only pain but also fear, stress and suffering (7), ethical questions about our use of fish must be carefully considered. From a young age many junior anglers are reassured fishing doesn’t really hurt the fish. In accepting pain sentience in fish however, so must we accept the serious impact invasive and tissue damaging practices must have upon these creatures. The methods utilised by anglers, in particular the ‘catch and release’ practices commonly employed by recreational fishermen are rendered questionable, indeed even their participation in recreational fishing is morally problematic in itself.  

Though we are far from fishing being utilised purely for necessity, it is vital that until this point any  individual captured, whether through recreational or commercial means, is dispatched rapidly and humanely. When determining the most ethical method of fish euthanasia, research advocates that rapid cooling is the most humane practice, resulting from a faster time to death and fewer signs of distress in experimental individuals (10, 11) . Fish should therefore be placed within an ice slurry immediately upon capture as a standard practice, as well as such humane methods being considered for other marine species in the commercial fishing industry. Though fish are afforded some legislative protection in regards to methods of their capture and handling, individuals of particular concern are octopus. These highly intelligent animals have impressive maze solving abilities, thereby indicating a great capacity for higher brain function, yet they remain unprotected by the  Animal Welfare (Commercial Slaughter) Code of Welfare 2016 (12).  It is therefore of paramount importance that research into invertebrate pain comprehension continues so we might better know how to regard these creatures, and potentially, prevent millions of needlessly painful deaths each year.

 

REFERENCES:

 

  1. Kris-Etherton, P. M., Harris, W. S., Appel L.J. (2002). Fish consumption, fish oil, omega-3 fatty acids, and cardiovascular disease. Circulation.  106, 2747-57.
  2. British Heart Foundation. (2016). BHF UK Factsheet: Cardiovascular Disease Statistics, viewed on 5th January 2017, <https://www.bhf.org.uk/research/heart-statistics>
  3. Rose, J. D. (2002). The Neurobehavioral Nature of Fishes and the Question of Awareness and Pain. Reviews in Fisheries Science, 10, 1–38.
  4. Broom, D. M. (2001). Evolution of pain. In: Soulsby, E. L. J, and Morton, D. (eds.), Pain: Its Nature and Management in Man and Animals (London, U.K.: Royal Society of Medicine Press, 17-25).  
  5. Yue, S. (2008). An HSI Report: Fish and Pain Perception. Humane Society International, viewed on 6th January 2017, <http://www.hsi.org/assets/pdfs/hsi-fa-white-papers/fish_and_pain_perception.pdf>
  6. Cooke, S. J., & Sneddon, L. U. (2007). Animal welfare perspectives on recreational angling. Applied Animal Behaviour Science . 104, 176-98.  
  7. Sneddon, L. U. (2006). Ethics and Welfare: Pain Perception in Fish. European Association of Fish Pathology, 26, 1-8.   
  8. Sneddon, L. U., Braithwaite, V. A. & Gentle, M. J. (2003a). Do fish have nociceptors: evidence for the evolution of a vertebrate sensory system. Proceedings of the Royal Society of London B. 270, 1115-1122.
  9. Sneddon, L. U., Braithwaite, V. A. & Gentle, M. J. (2003b). Novel object test: Examining nociception and fear in the rainbow trout. Journal of Pain. 4, 431-440.
  10. Wilson, J. M., Bunte, R. M. & Carty, A. J. (2009). Evaluation of Rapid Cooling and Tricaine Methanesulfonate (MS222) as Methods of Euthanasia in Zebrafish (Danio rerio). Journal of the American Association for Laboratory Animal Science. 48, 785-789.
  11. Blessing, J. J., Marshall, J. C. & Balcombe, S. R. (2010). Humane killing of fishes for scientific research: a comparison of two methods. Journal of Fish Biology. 76, 2571–257.
  12. Code of Welfare: Commercial Slaughter (2016). New Zealand Government, viewed on 1st February 2017, <https://www.mpi.govt.nz/document-vault/1409>
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