Archerfish can shoot straight because they have the ability to see straight, according to a study to be published in an upcoming issue of the Proceedings of the Royal Society B: Biological Sciences.
Shelby Temple and coauthors, studied the visual ability of Largescale archerfish (also known as the seven-spot archerfish, Toxotes chatareus) to detect small, camouflaged insect prey against a visually complex background of overhanging foliage. They did so by studying the visual adaptations that enable the archerfish to see so well both above and below the water (since the fish can only detect prey with visual cues at the air-water interface).
The authors used microspectrophotometry to characterise the spectral absorbance of photoreceptors in the retina, and found that the archerfish have differentially tuned the rods and cones there to correlate with the spectral differences in aquatic and aerial fields of view. The fish also aligned the maximum visual resolution of the eye with their preferred spitting angle.
According to lead author Shelby Temple, the results of the study provided empirical evidence for the functional role of differences in colour vision across the eye, a phenomenon present in most vertebrate groups.
"The correlation we found between the colour sensitivity of the archerfish eye for 'looking' in different directions and the background environment in those different directions indicates that the archerfish eye is highly tuned to differences in the spectral quality of light in different directions," he said.
"Our findings might help to solve why such intraretinal differences exist in so many other vertebrate eyes."
For more information, see the paper: Temple, S, NS Hart, NJ Marshall and SP Collin (2010) A spitting image: specializations in archerfish eyes for vision at the interface between air and water. Proceedings of the Royal Society B: Biological Sciences, doi: 10.1098/rspb.2010.0345.