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Do Fish Perceive Anaesthetics as Aversive?

 
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The use of fish as a substitute for mammals in laboratories has skyrocketed into the millions. Little research has been done on the effects of anesthetics that are used on fish during surgical procedures and euthanasia. This study tested nine anesthetics on Danio zebrafish for reactions that indicated discomfort, distress or pain. Seven of the anesthetics, including two of the most widely used, caused aversive reactions. The authors conclude that they are inhumane, and should be discontinued. They also call for similar tests for other types of fish, since reactions can vary from species to species.


Abstract:
[Abstract excerpted from original source.]

"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."

Spot Check Number: 2488
Sponsor: Brixham Environmental Laboratory (AstraZeneca) and University of Bristol
Researcher/Author: Gareth D. Readman et al.
Animal Type: Marine Animals
Record Type: Academic paper, Data and statistics, Journal article
Research Method: Experimental/Modeling/Applications
Geographic Region: Worldwide
Number of Participants: 120
Population Descriptors: Danio zebrafish (Danio rerio)
Year Conducted: 2013
Note that this research study is based at least in part on experiments on animals. HRC does not condone or endorse any animal research; we post this item (and others like it) with the hope that these findings can assist advocates in their work to help animals. For a description of how we select items for the HumaneSpot.org database, please click here.
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Use of anesthetics in fish

Just because a substance is aversive to an animal does not mean that it causes suffering. Mammals do not like the smell of most gas anesthetics and will avoid them if possible, but that does not mean the anesthetic causes them any suffering. However, I agree that it would be better to use the 2 agents that were not aversive to initially induce anesthesia where possible.

Groundbreaking

This research is groundbreaking, and if the recommendations are heeded, can help reduce suffering of millions of fish. Of course, I'm sure we'd all prefer they stop experimenting on animals altogether though.

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