A series of studies has recently revealed that reef fish are surprisingly adaptable. Freshly caught wild fish quickly learn new tasks and can learn to discriminate among colours, patterns and shapes, including those they have never encountered. These studies suggest that learning and interpreting new stimuli play important roles in the lives of reef fish.

To test the ability of fish to learn to discriminate shapes, a research team led by Ulrike E. Siebeck at the University of Queensland in Brisbane, Australia, trained damselfish to feed from a tube to which they attached a variety of visual stimuli. The latter included a three-dimensional latex disc, a two-dimensional blue disc painted on a plastic board, or black circles or propeller patterns on white boards. The fish were rewarded with food when they repeatedly tapped the stimulus—not the tube—with their snout or mouth.

The fish rapidly learned this task. The researchers then presented the fish with the original stimulus and one alternative distracting shape—bars versus discs, squares versus discs, or circles versus propellers, and the fish had to nose the shape they had been trained to tap in order to receive a reward. The fish tapped the correct shape about 70 per cent of the time in the first trial; this improved to 80 per cent to 90 per cent in subsequent trials.

Remarkably, the fish also learned when the food reward was delayed and delivered far from the stimulus. The damselfish exhibited what is called anticipatory behaviour—they would tap the image and then swim to the other end of their tank in anticipation of food.

... contd.