Anesthetic Activity of Acetylated MS-222 in Tilapia (Oreochromis Niloticus)

Abstract

A group of 8 tilapia (Oreochromis niloticus) were anesthetized once per week for six consecutive weeks, using tricaine methanesulfonate (MS-222) in the water. Time for the fish to reach anesthesia decreased significantly over the first four weeks, and then plateaued at about 27% below the first anesthetic exposure. These results suggest induction of the liver enzymes that convert MS-222 into metabolites, one or more of which have higher anesthetic activity than the parent compound. Major metabolites of MS-222 have been identified as part of regulatory studies evaluating residue persistence in food fishes. One of these metabolites, N-acetyl-3-aminobenzoic acid ethyl ester, which is acetylated MS-222, was selected for testing of anesthetic activity in tilapia. This report shows results of the testing, and speculates as to the potential utility of the acetylated metabolite of MS-222 as an alternate anesthetic agent in fish.