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Upper Midwest Environmental Sciences Center

Fisheries Restoration

The Availability of Freshwater Fish to the Angling Public Following Electrical Immobilization and Sedation by Benzocaine or Eugenol

Co-principal Investigators, Kim Fredricks, Mark Gaikowski, and Jeff Meinertz

Impact of UMESC Science

The results from studies associated with this project will be used to determine the effect that chemical sedation has on a fish’s feeding behavior.  These data will ultimately be used to support the potential approval of an immediate release fish sedative that can be efficiently used by fishery management agencies.


Sedatives are primarily used in aquaculture and fishery management to immobilize fish for handling and transport.  In the field, fishery management agencies often capture fish using electroshocking techniques.  After capture, fish are immersed in a chemical sedative bath for a short period of time so they can be easily handled for fin clipping, tag implantation, and weight and length measurements.  A concern surrounding the use of a chemical to sedate fish is the potentially harmful chemical residues that may be remaining in the fillet tissue after the fish has been sedated.  If those residues are harmful to humans, there is some risk that a recently sedated fish released to public waters may be caught and consumed by an angler.

Presently, tricaine methanesulphonate (or MS-222; available as Finquel® and Tricaine-S®) is the only fish sedative approved by the U.S. Food and Drug Administration (FDA).  Use of this sedative in the U.S. is constrained by a 21-day withdrawal period, i.e. fish cannot be made available for human consumption for 21 days after exposure.  Because of a lack of understanding of the toxicity of MS-222’s residues, the 21-day withdrawal period was established to allow the drug residues to deplete from the edible fillet tissue.  The studies that are needed to reduce the withdrawal time for MS-222 are cost prohibitive.

Two chemicals were selected for development as sedatives with short withdrawal times, benzocaine and eugenol.  Previously, the FDA stated it would not likely approve a general use “zero-h withdrawal” sedative, i.e., a sedative that could be used in general aquaculture and allowed for fish to be sacrificed for human consumption immediately after fish were removed from the sedative bath.  With this understanding, a decision was made to develop a sedative that could be used only by fishery management agencies and would allow for the immediate release of sedated fish.  Approval of an “immediate release” sedative for use by fishery management agencies seemed more likely because (1) fish were thought not to feed following capture and subsequent chemical sedation, (2) fishery management agencies would be processing (exposing fish to a sedative) only small portions of the total fish populations in any given lake or stream, and (3) the likelihood of any one person consuming fish sedated for fishery management purposes is extremely small considering the relatively small part of the U.S. population that catches and consumes wild fish.  The study described in this report was designed to address the hypotheses that sedated fish would not feed immediately after recovering from sedation and therefore would not be available for harvest by angling and subsequent consumption.


Determine the time that passes before fish express feeding behavior after electrical immobilization and sedation benzocaine or eugenol.

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