Use of Tricaine Methanesulfonate (MS222) In a Model of Minimum Anesthetic Concentration Determination in Goldfish (Carassius auratus)
College of Veterinary Medicine, North Carolina State University, Raleigh, NC, USA
Teleost fish demonstrate the neurophysiological capacity to experience pain and analgesia. Current methods of assessing pain and analgesia in fish suffer from methodological constraints. A common, objective model to assess the effects of analgesic drugs is determination of the minimum anesthetic concentration (MAC), defined as the minimum concentration of anesthetic at which 50 percent of a population fails to respond to a noxious stimulus. To lay groundwork for the use of a MAC depression model in teleost fish, we investigated the feasibility and utility of a MAC determination model in goldfish (Carassius auratus).
A population of 44 sarasa comet goldfish was tested (average weight 30 grams). Fish were individually immersed in MS222 for 4 minutes and subsequently evaluated for response to a supramaximal stimulus (25-gauge needle insertion into epaxial muscles). MS222 concentration for each fish was determined according to an up-down method of population sampling, starting at 160 parts per million (ppm) and proceeding in increments of 10 ppm based on a positive or negative response of the previous fish. Initial MAC (MACi) was determined 6 times in 1 week. As part of a separate ongoing project, fish were then anesthetized with MS222 for 8 minutes weekly for 7 weeks. MAC was also determined following saline injection (MACsal) at week 3. At week 8, final MAC (MACf) was re-determined 6 times within 1 week.
MACf (mean 182 ppm, SD 7.5 ppm) was significantly different from MACi (mean 162 ppm, SD 7.5 ppm) (p = 0.018). MACsal (170 ppm) was not significantly different from MACi (p > 0.05) but was significantly different from MACf (p<0.001). We conclude that MS222 allowed consistent and repeatable MAC determination in the short term, but MAC increased over time and/or repeated exposure. Repeated exposure to MS222 may increase anesthetic needs in fish, and may also limit the usefulness of a MAC depression model for studying analgesic effect of drugs in teleost fish.