Do Fishes feel pain?

Looking at a hooked fish or a fish asphyxiating in a drying stream, one cannot help but attribute human feelings of pain and suffering to the fish. But do fishes really feel pain? The jury is still out! Different researchers have come to different conclusions.

A team of researchers led by Dr Lynne Sneddon in Scotland have concluded that fishes do feel pain. Other researchers do not agree.

Sneddon's conclusion was based on work with Rainbow Trout. There are receptors in the brains of Rainbow Trout that appear to be virtually identical to those responsible for the detection of pain in humans. The injection of bee venom and acid into the lips of Rainbow Trout resulted in the transmission of a nervous response and modification of the behaviour of the fish. In some cases abnormal behaviour resulted after injury. After the administration of the pain killer, morphine, the fish’s behaviour returned to ‘normal’.

In her 2010 book 'Do Fish Feel Pain?', Victoria Braithwaite argues that fishes are more intelligent than previously thought and have structures in the brain that allow them to feel pain. The book raises serious questions about the treatment of fishes. Interestingly she states that the trigeminal nerve contains both fast and slow firing nerve fibres (those responsible for reflexes and pain) but the percentage of 'pain fibres' is significantly lower in the test fish (a trout) than in mammals and birds.

Dr J. Rose of the University of Wyoming on the other hand states that the perception of pain and fear in fishes is very different from that of humans. See below for Rose and colleague's 2014 paper for additional information.

He argues that it is important to first distinguish between pain and the reception of noxious (harmful) stimuli (nociception). Without doubt both fishes and humans respond to noxious stimuli. A fish that has been hooked is obviously responding to a stimulus. Likewise, if you burn yourself, you will very quickly respond to the stimulus, however this response occurs before you feel any pain. Nociception is controlled by the spinal cord and brainstem.

Rose states that the difference in the perception of pain and fear in fishes and humans results from differences in brain structure. The human brain has a massively developed cerebral cortex (the grey folded outer layer). Pain and fear in humans results from the stimulation of several regions of the cerebral cortex. Rose states that the tiny cerebral cortex of fish brains lack these regions. The lack of the comparable regions of the brain is one of the arguments that Rose uses to conclude that fishes do not experience pain and fear.

Most of the "everyday behaviour" of a fish is controlled by the brainstem and spinal cord. Experiments in which the cerebral hemispheres of fishes were removed have shown that even without these parts of the brain, fishes can maintain normal function and behaviour. Interestingly a human with complete destruction of the cerebral cortex will still respond to noxious stimuli, but feels no pain.

More recently, Brian Key, Head of the Brain Growth and Regeneration Lab at the University of Queensland stated that fishes lack the regions of the brain that are necessary to feel pain. In his words, "Using this strategy, I conclude that fish lack the necessary neurocytoarchitecture, microcircuitry, and structural connectivity for the neural processing required for feeling pain.” For more information see Related links below.

Whether fishes do or do not feel pain as we know, they most definitely suffer from stress. Rose states that they "display robust nonconscious, neuroendocrine and physiological stress response to noxious stimuli".

In short, if you need to touch a fish, you should remember that the fish may (or may not) experience pain the way you do, but it undoubtedly does suffer from stress. Professional ichthyologists follow stringent guidelines to reduce stress when handling fishes.

Related links

1. Fish Feel No Pain - Dr Karl's 'Great Moments in Science'
2. Fear smells like sugar to fish
3. Key, Brian (2016) Why fish do not feel pain Animal Sentience 2016.003

Further reading

1. Barker, D., Allan, GL, Rowland, S.J. & Pickles, J.M. 2002. A Guide to Acceptable Procedures and Practices for Aquaculture and Fish Research. NSW Fisheries. Pp. 52. ISBN 0 7310 9423 9.
2. Braithewaite, V. 2010. Do Fish Feel Pain? Oxford University Press. Pp 256.
3. Chandroo, K.P., Yue, S. & R.D. Moccia. 2004. An evaluation of current perspectives on consciousness and pain in fishes. Fish and Fisheries. 5: 281-295.
4. Huntingford, F.A., Adams, C., Braithwaite, V.A., Kadri, S., Pottinger, T.G., Sandoe, P. & J.F. Turnbull. 2006. Current issues in fish welfare. Journal of Fish Biology. 68: 332-372.
5. Jackson, C. 2003. Laboratory Fish: Impacts of Pain and Stress on Well-being. Contemporary Topics. 42 (3): 62-73.
6. Key, Brian (2016) Why fish do not feel pain Animal Sentience 2016.003.
7. Oidtmann, B. & R.W. Hoffmann. 2001. Schmerzen und Leiden bei Fischen (Pain and suffering in fish). Berl. Münch. Tierärztl. Wschr. 114: 277-282.
8. Randerson, J. 2003 Does a hook hurt a fish? The evidence is reeling in. New Scientist May: 15.
9. Rose, J.D. 2002. The Neurobehavioral Nature of Fishes and the Question of Awareness and Pain. Reviews in Fisheries Science. 10(1): 1-38.
10. Rose, J.D., Arlinghaus, R., Cooke, S.J., Diggles, B.K., Sawynok, W., Stevens, E.D. and C.D.L. Wynne. 2014. Can *fish* really feel pain? Fish and Fisheries. 15 (1): 97-133.
11. Sneddon, L.U. 2006. Ethics and welfare: Pain perception in fish. Bulletin of European Association of Fish Pathologists. 26(1): 7-11.
12. Sneddon, L.U., Braithwaite, V.A. & M.J. Gentle. Do fishes have nociceptors? Evidence for the evolution of a vertebrate sensory system. Procedings of the Royal Society of London. Series B-Biological Sciences. 270 (1520): 1115-1121.