Figure 1. The archer fish can distinguish between two coloured targets.

A. The stimulus sequence entails presenting the archer fish with two black circular targets. The trial began when one of the two targets was flashed red and the other green for 66 ms, after which the targets turn black for T = 1 s. The fish's task was to detect and shoot at the red target, for which it was rewarded with a food pellet (see supplementary movie S1). The targets continued to flash for 66 ms every T = 1 s with the same colour and intensity until the fish shot a target. The location (right/left) of the red target and its colour intensity were varied from trial to trial. The fish had a single attempt to shoot at each trial. B. Frame from a video of an archer fish shooting the left target. This is the correct selection since the left target flashed red (video frame in inset) 0.6 s before the shot. C. Success rates (mean ± S.E.M.) of the two fish together with response time histograms (note that the time is measured with respect to the first flash, i.e., from the moment the fish was provided with colour information). Both fish achieved very high accuracies in detecting the flashing red target. In addition, the response time histograms, which show that most of the shots were made less than 1 s after the first flash, indicate that the fish can make a decision on the basis of information from a single flash.