The colors of reef fish will perpetually dazzle both experienced aquarists, as well as casual aquarium and wildlife observers. When considering the endless rainbow of colors found on reefs, we’re quick to assume that the fish living among the vivid reefs can see and appreciate the same array of colors that we do. A little [...]
The colors of reef fish will perpetually dazzle both experienced aquarists, as well as casual aquarium and wildlife observers. When considering the endless rainbow of colors found on reefs, we’re quick to assume that the fish living among the vivid reefs can see and appreciate the same array of colors that we do. A little deeper look into has unveiled some interesting facts, which reach far beyond the fish world.
It’s hard to imagine any ecosystem that is as flooded with as much color as a coral reef. The vivid color palette must serve a biological purpose and be critical to reef denizens, right? Professor Justin Marshall of the University of Queensland’s Queensland Brain Institute decided that a little more of an understanding, aside from speculation, needed to be established. So, he, and numerous colleagues from the Sensory Neurobiology Group within the Queensland University department, focused to see exactly how some reef fish see. In particular, he examined the eyes of a diverse and colorful group–the Triggerfish.
What he found was not only unexpected, but also quite applicable to an enormous variety of animals. Marshall found a large quantity of “double cones” in the eyes of Blackbar Triggerfish (Rhinecanthus aculeatus). This alone is not too amazing or unexpected, as these structures are found in the eyes of many animals, including some non-placental mammals, as well as in other vertebrates such as fish, reptiles, and amphibians. Cones, in general, are photoreceptor cells found in the retina, which accept and register bright light. The “double cones” are two cones which are fused together. The function of double cones has always been suggested to be for non chromatic purposes, such as motion, polarized vision, and luminance. But, all such speculation was realistically to disguise the unknown prupose for these cells.
Marshall’s work has shown something quite different and previously unknown; it has provided evidence that these double cones are, in fact, used for color vision as “independent spectral channels”. Says Marshall, “These photoreceptors are not present in human retina or other placental mammals and, perhaps as a result, we have overlooked the fact that we do not know what they do. This is odd as they are the commonest photoreceptor in the eyes of most diurnal animals and these new results show for the first time that in the trigger fish, a colorful inhabitant of The Great Barrier Reef, these cones are used for color vision.”
This revelation on the purpose and function of a relatively common, yet misunderstood, part of one of the most amazing organs in complex animals may shed some light into the vision and abilities of not only reef fish, but other animals which share these double cone structures.
Vincenzo Pignatelli, Conor Champ, Justin Marshall, and Misha Vorobyev. Double cones are used for colour discrimination in the reef fish, Rhinecanthus aculeatus Biol Lett 2010
[flickr : christian]
