The efficacy of three types of analgesic drugs in reducing pain in the rainbow trout, Oncorhynchus mykiss

Recent research has shown the possibility of pain perception in fish; therefore, the use of analgesia or “painkillers” should be considered for invasive procedures. However, there is relatively little information on the effectiveness of analgesic drugs nor on the appropriate dose for fish. This study assessed the efficacy of three types of drug: an opioid, buprenorphine, a non-steroidal anti-inflammatory drug (NSAID), carprofen and a local anaesthetic, lidocaine. Each drug was tested at three doses on rainbow trout that were noxiously stimulated and the most effective dose was also given to fish experiencing no pain to investigate side-effects. Ventilation rate and time to resume feeding were used as pain indicators, together with the amount of activity and plasma cortisol concentrations to gauge any detrimental side effects. Buprenorphine at all three doses had limited impact on the fish's response to a painful stimulus. Carprofen ameliorated effects of noxious stimulation on time to resume feeding but activity was reduced more than by noxious treatment alone. Lidocaine reduced all of the pain indicators measured with the lowest, most effective dose being 1 mg per fish. None of the analgesics led to raised plasma cortisol compared to control groups. This study demonstrates that lidocaine could be recommended for use in rainbow trout to ameliorate possible pain-related responses.