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There are four groups of analgesics in fish commonly referred to into the literature 1-10: opioids, local anaesthetics, non-steroidal anti-inflammatories and antidepressants - the latter two, lesser explored in fish.
Experimentally, the opioid morphine (5 mg/kg) has been shown to minimize pain and discomfort in rainbow trout, flounder and goldfish 8. It is assumed that morphine actions pharmacokinetically in fish similar to its action
in mammals, by inhibiting neurotransmitter release, thus blocking nociceptors and central transmission (presynaptic effect). Except that in fish, excretion rates are much slower (total elimination time = 56 hours), suggesting that its use would be suitable to chronic conditions or after major surgery 8. Other opioids, such as tramadol, dermophine, butorphanol and buprenorphnine were also tested on farmed and ornamental fish species, such as cod, trout, carp, dogfish and koi carp, but it appeared to have limited effectiveness and poor analgesic properties 8.
Local anaesthetics block nociceptive transmission. Lidocaine analgesic effects were tested in rainbow trout and zebrafish where, at 1 mg/kg, no side effects were observed, and it was assessed as a very efficient analgesy 8. Novocaine is known to reduce reflex responses in cod 3, but since it has not been tested in vivo in fish, its use is not recommended.
Very few non-steroidal anti-inflammatories (NSAI)
have been assessed with respect to their analgesic effects in fish, by taking into account NSAIs properties observed in other species, which refer to the decrease
of inflammatory reaction by decreasing production of thromboxanes and prostaglandins. Ketoprofen, tested in Koi carp and dogfish with doses ranging between 2 and 4 mg/kg, was proven as not effective, whereas carprofen at doses of 1-5 mg/kg, was found to cause deleterious effects in trout, i.e. increased ventilation and depressed activity 8, 10.
Physical means • Gradual cooling to 10.3 ˚C was proven as effective in adult zebrafish (D. rerio) to a degree where surgical plane of anaesthesia is achieved. However,
it is advised that gradual cooling to be used as a last option and when surfaces and instrumentation can be maintained at 10 ˚C 3.
Chemical means • There are currently over 15 anaesthetics in use in veterinary practices, experimental settings and aquaculture. The most common
An Urban Experience
anaesthetics are: tricaine methanesulfonate (MS222), benzocaine, lidocaine hydrochloride, clove oil, eugenol, isoeugenol, etomidate and metodmidate hydrochloride, 2-phenoxyethanol (2-PE), quinaldine and quinaldine sulpohnate, 2,2,2 tribromethanol (TBE), propoxate, 4-Styrilpyrydine, propofol and isoflurane. However, only very few of them are approved for use in fish destined for human consumption.
A summary of the anaesthetic agents applied to fish, showing a range of doses, efficiency and side effects of the anaesthetics in different fish species will be discussed during the lecture. It is important to emphasize that
these data will refer to certain species and conditions of use, such as water temperature and pH, body size and physiological status.
As a general recommendation, in instances where there is no prior experience with the fish, fish strain and/or analgesic or anaesthetic substances, a pilot test using the lowest doses and a small number of fish of different strains to be carried out, to ensure safety and efficacy of the procedure.
1. Readman GD, Owen SF, Murrell JC, Knowles TG (2013) Do Fish Perceive Anaesthetics as Aversive? Plos One 8: 7 [PubMed]
2. Nordgreen J, Tahamtani MF, Janczak MA, Horsberg TE (2014) Behavioral Effects of the Commonly Used Fish Anaesthetic Tricaine Methanesulfonate (MS- 222) on Zebrafish (Danio rerio) and its Relevance for the Acetic Acid Pain Test. PLoS One. 2014; 9(3): e92116. 2014 Mar 21. doi: 10.1371/journal.pone.0092116 PMCID: PMC3962382
3. Collymore C, Tolwany A, Lieggi C, Rasmussen S (2014) Efficacy and Safety of 5 Anesthetics in Adult Zebrafish (Danio rerio). J Am Assoc Lab Anim Sci.2014 Mar; 53(2): 198-203
4. Collymore C, Banks EK, Turner PV (2016) Lidocaine Hydrochloride Compared with MS222 for the Euthanasia of Zebrafish (Danio rerio). J Am Assoc Lab Anim Sci. 2016 Nov;55(6):816-820
5. Davis DJ, Klug J, Hankins M, Doerr MH, Monticelli RS, Song A, Gillespie HC, Bryda EC (2015) Effects of Clove Oil as a Euthanasia Agent on Blood Collection Efficiency and Serum Cortisol Levels in Danio rerio. J Am Assoc Lab Anim Sci. 2015 Sep; 54(5): 564–567
6. Sladky KK, Swanson CR, Stoskopf MK, Loomis MR, Lewbart GA (2001) Comparative efficacy of tricaine methanesulfonate and clove oil for use as anesthetics in red pacu (Piaractus brachypomus). Am J Vet Res 62: 337–342 [PubMed]
7. Gil WH, Ko GM, Lee HT, Park I, Kim SD (2016) Anesthetic Effect and Physiological Response in Olive Flounder (Paralichthys olivaceus) to Clove Oil in a Simulated Transport Experiment. Dev Reprod. 2016 Sep; 20(3): 255–266. doi: 10.12717/DR.2016.20.3.255[PubMed - indexed for MEDLINE]
8. Sneddon LU (2012) Clinical Anesthesia and Analgesia in Fish. Journal of Exotic Pet Medicine 21: 32–43
9. Chervova LS (1997) Pain sensitivity and behavior of fishes. J Ichthyol 37:98- 102
10.Mettam JM, Oulton LJ, McCrohan CR, Sneddon LU (2011) The efficacy of three types of analgesic drug in reducing pain in the rainbow trout, Oncorhynchus mykiss. Animal Science, Veterinary Medicine and Zoology In: Animal Studies Repository

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