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The availability of safe and effective fish sedatives is crucial to fisheries researchers, managers, and aquaculturists. Fisheries professionals sedate or anesthetize fish for a variety of purposes, ranging from simple handling to invasive surgical procedures. Although the specific constraints differ from one situation to the next, ideally a fish sedative is safe and easy to administer, is effective at low doses (minimizing the amount needed for field applications), sedates fish quickly and predictably, has a reasonable margin of safety with respect to oversedation, can be used over a broad range of water chemistries, is inexpensive, and allows for rapid recovery from sedation and its effects (Bowker and Trushenski 2011). Additionally, in field research, it is particularly advantageous if sedative use does not require treated fish to be held to complete a withdrawal period prior to release (i.e., they can be released immediately).
At this time, there are few legal options for sedating fish, and those that are available are not always ideal in terms of their safety, efficacy, and practicality of use. Currently, there is only one sedative compound that is approved by the U.S. Food and Drug Administration (FDA) for the temporary immobilization of fish: tricaine methanesulfonate (commonly referred to as MS‐222). Two MS‐222 products are currently approved in the United States, but the use of these products is restricted to ictalurid, salmonid, esocid, and percid fishes (though they are approved for other fishes in laboratory or hatchery settings only) treated at water temperatures >10°C. Use of MS‐222 is further restricted by the 21‐d withdrawal period deemed necessary to allow for drug residue depletion prior to releasing treated fish into the wild (or otherwise making them available for human consumption). Although not approved by the FDA, carbon dioxide (CO2) is considered a drug of “low regulatory priority” (USFDA 2011) and its use allows fish to be released immediately after sedation. However, CO2 can be difficult to apply uniformly and is typically slow‐acting; adverse effects have also been reported (Neiffer and Stamper 2009). There are at least two additional drugs currently being investigated for use as fish sedatives, specifically, benzocaine and eugenol. These drugs can currently be used under the Investigational New Animal Drug exemptions held by the U.S....