Figure 1. Diagram of testing apparatus.

The testing apparatus, consisting of a light and dark side identical in size. During the initial preference determination period (a) we simply monitored the time spent on the two-sides of the tank (all fish tested preferred the light side). Fish were then exposed to one of three anaesthetics while in the light side of the tank (b). Once fish recovered we re-tested preference (following the identical procedure as used in panel a) with the apparatus once again free of anaesthetics (c).