A Portable Electronarcosis System for Anesthetizing Salmonids and Other Fish

The physiological responses of fish to continuous (nonpulsed) direct current were first described in the 1960s. One of these responses, electronarcosis (anesthesia, accompanied by muscle relaxation, through electrical inhibition), has been used in fisheries research and management as an anesthetic since the 1970s. We provide details on the assembly and operation of a portable electronarcosis unit for fish anesthesia and describe its performance with respect to two species of salmonids. The portability and effectiveness of this approach make electronarcosis a viable alternative to existing anesthetics that can be used for a number of applications. Anesthetics are used in fisheries research and management to sedate fish during, for example, biometric data collection, fish marking, and surgery. The goal is to induce a level of relaxation and reduced reaction to external stimuli that eases handling and reduces stress. For surgery, a state of complete relaxation with no rigidity in the musculature of the fish and no response to external stimuli is desired. Field studies require that an anesthetic must (1) allow for the immediate release of the fish into the food chain, (2) allow for swift induction of and recovery from anesthesia, and (3) not excessively disturb the physiological balance of the fish which would reduce its chances for survival upon release (Anderson et al. 1997). Historically, both chemical and physical (e.g., electronarcosis) stimuli have been used to anesthetize fish, although chemical anesthetics are more commonly used in field applications. Few anesthetics are currently approved by the U.S. Food and Drug Administration for use in fisheries applications. A commonly used chemical anesthetic, MS-222 (tricaine methanesulfonate), is problematic because it does not allow for the immediate release of the fish that could *Corresponding author: michael [email protected] Received June 8, 2010; accepted January 27, 2011 Published online May 5, 2011 be harvested (JSA 2007). Electronarcosis is an alternative form of anesthesia that probably meets the three criteria. The electrophysiological effects of continuous (nonpulsed) direct current (DC) on fish were first described and synthesized in the 1960s (Lamarque 1963, 1967; Vibert 1963, 1967) and are briefly reviewed here. Responses of fish facing the anode to DC elicited at differing voltage levels were characterized as a series of persistent behavior patterns ordered correspondingly to increased voltage: inhibited swimming, forced swimming, narcosis, pseudo-forced swimming, and tetany. Electronarcosis and tetany can often be confused because of the similar physical response of immobilization. However, tetany, more commonly associated with electrofishing, is a condition where the fish musculature is excited and the fish’s body is rigid. Once removed from the electrical stimuli, the musculature relaxes, though the fish may show signs of posttraumatic sedation. In contrast, electronarcosis occurs through the inhibition of medullary motor paths and supercedes the forced swimming response. During electronarcosis, no cerebral message reaches the motor paths, the fish loses equilibrium, and the muscles slacken. The fish remains in a state of narcosis with the body relaxed while submerged in water and exposed to DC within the appropriate voltage gradient range. It is not possible to physiologically achieve the narcotizing effect with AC or pulsed direct current (PDC) (Lamarque 1967). Many applications using the approach described herein require a prolonged state of narcosis and handling of fish in the electrical field. The relatively low DC voltage gradient probably translates to reduced stress and injury to the fish, and a safer working environment for the handler. Electronarcosis has been used in a variety of applications since the effects of electricity on fish were first investigated in 335 D ow nl oa de d by [ K ay H ol zw ei ss ig ] at 1 2: 57 1 8 Fe br ua ry 2 01 3