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Research Training Scholarships

Jessica Mettam

“Detection and alleviation of pain in fish”

The issue of fish welfare has been an area of increased interest and activity in recent years and UFAW has been at the forefront of supporting this work. Very large numbers of fish are subjected to invasive procedures during capture and farming and are increasingly being used in scientific research. However, the question of whether or not fish experience pain is controversial. Pain includes both a sensory and emotional component and some scientists argue that fish do not have the necessary neural anatomy for consciously experiencing pain and merely show reflex responses during nociception i.e. although fish have nociceptors that can respond to aversive stimuli in the environment, there is still debate over whether fish can actually ‘feel’ pain.

Jessica Mettam, under the supervision of Dr Lynne Sneddon at the University of Liverpool, was awarded a UFAW Animal Welfare Research Training Scholarship in 2005 to study the capacity for pain in fish and to determine methods of alleviating pain. Jessica sought to address three key questions: which brain areas in fish show activity during noxious stimulation; whether chemoreceptors innervated by the trigeminal nerve have a solely nocicieptive function; and what analgesic is most effective in reducing aversive responses to potentially painful stimulation.

Firstly, Jessica conducted an experiment on common carp to investigate their reaction to a noxious stimulus (injection of acetic acid) with collaborators at the University of Antwerp. Jessica found that there were prolonged changes in fish brain activity (measured using functional magnetic resonance imaging (which detects changes associated with blood flow), using blood-oxygen-level-dependent (BOLD) contrast) following noxious stimulation and changes were related to stimulus intensity. Furthermore, activity patterns were more intense during noxious stimulation and were not confined to the hindbrain suggesting that higher processing in the forebrain and midbrain of fish occurred in response to nociception rather than just a reflex response.

Jessica also investigated the properties of chemical sensitive receptors on the head of rainbow trout. Overall, she found that chemically sensitive trigeminal nociceptors did not respond to non-noxious agents, but preferentially responded to noxious chemicals (acetic acid, carbonated water, citric acid, low pH and concentrated sodium chloride). This has implications for fish exposed to contaminants of low PH and increasing carbon dioxide in the aquatic environment since their welfare may be compromised.  

Finally, Jessica considered the effect of three pain-relieving drugs (buprenorphine, carprofen and lidocaine) on rainbow trout. Ventilation rate, time to resume feeding, overall activity and rate of mouthing gravel were all adversely affected in noxiously treated fish. Only carprofen and lidocaine were effective, however, lidocaine was the only drug not to elicit behavioural or physiological side-effects. Thus analgesia alleviated responses to noxious treatment suggested the alleviation of pain.

Jessica concluded that the evidence from her experiments supported the growing body of literature suggesting that fish might fulfil some of the criteria for pain perception to occur in rainbow trout.


Published papers arising from Jessica’s project supported by UFAW:

Mettam, J. J., Oulton, L. J., McCrohan, C. R., & Sneddon, L. U. 2011. The efficacy of three types of analgesic drugs in reducing pain in the rainbow trout, Oncorhynchus mykiss. Applied Animal Behaviour Science. 133(3): 265-274. http://dx.doi.org/10.1016/j.applanim.2011.06.009

Mettam, J. J., McCrohan, C. R., & Sneddon, L. U. 2011. Research Article: Characterisation of chemosensory trigeminal receptors in the rainbow trout, Oncorhynchus mykiss: responses to chemical irritants and carbon dioxide. Journal of Experimental Biology. 215: 685-693. http://dx.doi.org/10.1242/jeb.060350