A new study just published in the open access journal PLoS ONE shows how practices in research laboratories can be made more animal friendly. Fish are the most commonly used research animal in Canada, and at the end of an experiment laboratory fish are typically killed by emersion in a chemical anaesthetic. UBC researchers devised a clever experiment to ‘ask ‘ the fish how they evaluated different anaesthetics, including the most common agent ,TMS (also known as MS-222). Fish were tested in a tank with two compartments, and were trained to associate a food reward with the ‘light’ side of the tank. After training all fish spent almost all their time in this side of the apparatus, and would immediately enter the light side when placed into the test apparatus. The fish were then exposed to one of the anaesthetics while in the light side of the tank. All fish lost consciousness and were allowed to recover in another tank. When fish were then retested (with the test apparatus now cleaned of all chemicals), all fish that had been exposed to the TMS now avoided the light side. This type of conditioned place avoidance response indicates that the fish learned to associate the previously positive environment with some negative effect of the TMS. Fish exposed to the other agents (clove oil and metomidate) showed much less evidence of aversion. This research suggest that researchers using fish should avoid the use of TMS as an anaesthetic or euthanasia agent.