Updated Review of Fish Analgesia

Analgesics are an integral part of routine pain management in mammals, yet their use in fish is still limited. Some recommendations on the use of analgesics in fish are currently in the literature; however, information on the properties of analgesic drugs in most fish species is still scarce and sometimes misleading. The present review of information on the use of analgesics in fish was thus compiled to help clinicians make an informed decision as to which drug and dose to use. The main agents that have been investigated are opioids, NSAID, and local anesthetics, primarily in rainbow trout and zebrafish. There is presently no overwhelming evidence of efficacy for most analgesics in fish, although beneficial effects on behavior and physiologic parameters have been reported in many instances, especially associated with morphine administration. Furthermore, most analgesics did not result in significant adverse side effects. Thus, analgesics could be administered whenever it is considered that an animal might experience pain, given that the drugs appear not to cause harm and may be beneficial. However, caution must be advised because 1) important interspecies variation has been reported and 2) unforeseen effects could affect experimental results. Further research is needed to investigate analgesic use in fish. This should be accompanied by research aimed at improving our knowledge of the various species of fish. The current lack of a validated approach to assessing pain in fish limits our ability to evaluate the efficacy of analgesics in fish.