Tricane methanesulfonate or MS-222 is a white crystalline powder that when added to water acts to sedate or anesthetize fish. MS-222 is registered by the FDA for use in certain species of fish intended for human consumption. However, FDA approval has not been granted for use of MS-222 with tilapia intended for human consumption.
MS-222 is rapidly soluble in water. Tilapia can be sedated at dosages of 20 to 50 mg/L and anesthetized at levels of 50 to 100 mg/L. Once added to water MS-222 will being to take effect on exposed fish within a few minutes. Behavioral changes suggestive of sedation include reduced reaction to stimuli and slowed rate of breathing. Deeper sedation to light anesthesia are reached when fish has partial loss of equilibrium. Deep anesthesia occurs with total loss of equilibrium, very slow ventilation and no response to external stimuli. If the fish stops ventilation or respiration, the animal should be removed immediately from the anesthetic solution and revived in water free of MS-222. Once removed from the MS-222 bath recovery may take 15 to 30 minutes. Rate of sedation, anaesthesia and recovery are influenced by water temperature. Elevated temperature speeds up these responses.
MS-222 can change the pH to more acidic when added to water. This complication is mitigated if the water is well buffered, eg. has adequate alkalinity to buffer the pH change. The alkalinity of water should be known if the water is to be used in an anesthetic bath. Water with alkalinity ó50 mg/L should either not be used in MS-222 anesthesia or the water first treated with a buffer (e.g. sodium hydroxide) to counter the low pH effect of MS-222.