A second behavioural trial (observer trial ) was conducted 24 h after the naïve trial. This tested the observer trout’s ability to establish a dominant/subordinate in less time than the original dyad, indicating greater cognitive performance. This was based on the premise that a trout that can recognise a con-specific it has previously observed, remember something of its attributes, and infer how its own attributes compare, will more quickly adopt a stable social position, either dominant or subordinate, than it would if presented with an unknown trout (Drew, 1993). The previous day’s observer trout was placed into a new trial tank with one from the original dyad (alternating initially dominant or subordinate with each trial replicate). Apart from the absence of a trout in an adjacent tank overlooking the dyad, the observer trial followed the same procedure as the naïve, with the former observer now as an active dyad participant.