To put archerfish vision into context, many other freshwater fish (for example zebrafish, cichlids) have visual acuities of less than 1-2 cycles per degree, whereas marine mammals (seals, whales, dolphins) have acuities ranging from 3.5 5.5 cycle per degree. Humans and other primates have acuity of around 60 cycles per degree. The best seem to be birds of prey with the wedge-tailed eagle having visual acuity of over 140 cycles per degree.
Dr Shelby said: "This huge range across animals is mainly because of the optical clarity of the media in which they see and the distances to their targets. While birds and land animals see through air and look for objects at distances of tens to hundreds of metres, fish and other aquatic animals have to see through water which at best gives only tens of metres of clarity.
"In the case of many freshwater fishes visibility of their water may be less than a few centimetres. Accordingly, archerfish have lower acuity in the part of the eye that looks down into the murky water and the highest acuity in the part of the eye that looks up and forwards."
|Contact: Hannah Johnson|
University of Bristol