Abstract
This study addresses a fundamental question in fish welfare: are the anaesthetics used for fish aversive? Despite years of routine general use of many agents, within both scientific research and aquaculture, there is a paucity of information regarding their tolerance and associated behavioural responses by fish. This study examined nine of the most commonly used fish anaesthetic agents, and performed preference tests using adult mixed sex zebrafish (Danio rerio), the most commonly held laboratory fish. Video tracking software quantified swimming behaviour related to aversion for each anaesthetic at 50% of its standard recommended dose compared with clean water in a flow-through chemotaxic choice chamber. Results suggest that several commonly used anaesthetics were aversive, including two of the most commonly recommended and used: MS222 (ethyl 3-aminobenzoate methanesulphate) and benzocaine. For ethical best practice, it is recommended that compounds that are aversive, even at low concentration, should no longer be used routinely for anaesthesia or indeed the first step of humane euthanasia of adult zebrafish. Two agents were found not to induce aversive behavioural responses: etomidate and 2,2,2 tribromoethanol. For the millions of adult zebrafish used in laboratories and breeding worldwide, etomidate appears best suited for future routine humane use.
Highlights
The EU Directive [1] and its predecessor in the UK the Animals (Scientific Procedures) Act (A(SP)A) [2] place great emphasis on improving the welfare of those animals undergoing regulated procedures in scientific experiments via implementation of the principles of Reduction, Replacement and Refinement
UK statistics from The Home Office for 2011 show that fish accounted for 563,903 procedures [3]
Hydrochloric acid was used as a positive control to assess the functionality of the system and to provide a model of aversive behavioural response
Summary
The EU Directive [1] and its predecessor in the UK the Animals (Scientific Procedures) Act (A(SP)A) [2] place great emphasis on improving the welfare of those animals undergoing regulated procedures in scientific experiments via implementation of the principles of Reduction, Replacement and Refinement (the 3Rs). Under the new EU directive [1] which updated A(SP)A [2] on the 1st of January 2013, fish in scientific studies are protected under law from the point at which they become capable of independent feeding. UK statistics from The Home Office (the relevant government regulatory body) for 2011 show that fish accounted for 563,903 procedures [3]. The majority of these fish were zebrafish. In addition to those within these official records, there were significant numbers of zebrafish which are held for breeding purposes, supplying embryos for testing and those used before the point of protection under A(SP)A (and not required to be reported). It is estimated that in excess of 600 academic establishments are working with zebrafish [4]
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