Guidelines for the Use of Fishes in Research
8. Final Disposition of Experimental Animals
Several methods are available to euthanize fishes. Various regulatory or granting agencies may require specific euthanasia methods and written protocols that demonstrate sufficient attention to humane treatment. Some methods for euthanasia are listed by American Veterinary Medical Association (AVMA) Guidelines for the Euthanasia of Animals: 2013 Edition (AVMA 2013, https://www.avma.org/KB/Policies/Documents/euthanasia.pdf), and general considerations in the Guide for the Care and Use of Laboratory Animals (NRC 2011).
In general, the procedures must be performed quickly and with minimal stress prior to dispatch. Spinal cord dislocation, or decapitation generally are acceptable methods, provided the procedure is performed quickly and accurately. Some IACUCs have approved protocols where small fish (<5 cm total length) may be euthanized by cold stunning in an ice bath (Wilson et al. 2009; Blessing et al. 2010). Small fishes may be euthanized instantly by immersion in liquid nitrogen following sedation (Schaffer 1997); however, this approach and its appropriateness should be discussed with an IACUC or other oversight body prior to use. Depending on the size of the fish and experimental needs, some form of physical anesthesia, such as hypothermia, may be indicated prior to euthanasia. Cold shock and electrical shock are used commonly by fish processors preparing large numbers of animals for slaughter, where fish may be considered commodities rather than research specimens. Small numbers of fishes can be euthanized by exposure to relatively high concentrations of sedatives such as MS-222; however, the use of MS-222 (AVMA 2013, https://www.avma.org/KB/Policies/Documents/euthanasia.pdf) and other chemical sedatives as euthanizing agents has not been approved by the FDA, and these chemically euthanized fishes may not be made available for human or animal consumption. See section 7.11 Restraint of Fishes: Sedatives and Related Chemicals. See Coyle et al. (2004) on anesthetic use with aquatic animals, including dosages used with commonly cultured fish species (Southern Regional Aquaculture Center fact sheet 3900 at https://srac.tamu.edu/index.cfm/event/getFactSheet/whichfactsheet/162/). Euthanasia through simple oxygen deprivation (dewatering) is sometimes practiced during mandated depopulation of production-level facilities; however, this procedure is not recommended for research situations. Stunning with an electroshock followed by rapid decapitation or cold shock is a suggested alternative if large numbers of fishes must be euthanized. Rotenone, which blocks oxygen uptake, has been useful in cases of the occurrence of unintended exotics (Rayner and Creese 2006) (see section 5.2.3 Representative Samples). Selection of euthanasia methods should be done in coordination with the institutional IACUC. Additional information is provided by The University of Florida Extension Service, where publications addressing methods of fish slaughter, killing, and euthanasia are reviewed (Yanong et al. 2007, http://edis.ifas.ufl.edu/pdffiles/FA/FA15000.pdf).