"Pain" and analgesia in fish: what we know, what we don't know, and what we need to know before using analgesics in fish

There is considerable pressure for Animal Care and Ethics Councils to recommend using analgesics in experiments that involve fish. Although we do have some data regarding this issue, I argue that we do not know enough to recommend any being used. For example, the doses of morphine used in fish experi- ments range from 10 to 3000 mg/kg relative to doses used in mammals that typically range from 2 to 5 mg/ kg. I recommend that we continue to use anaesthet- ics that are commonly used with fish (tricaine, benzo- caine, and eugenol) because these also probably act as analgesics in fish as they do in mammals, and thus, may have some analgesic properties post-operatively. There are no adequate tests that would allow us to recommend using analgesics for farmed fish that may be consumed by humans or pets.