Tuesday, March 29, 2011
Malacosteus niger, the Black Dragonfish
Malacosteus niger is a member of a group of deep water fish known as Dragonfish or Loose-jaws. More commonly known as the Black Dragonfish, this denizen of the deep has stumbled upon an evolutionary cheat code. It has stealth vision.
Most organisms in the deep oceans can only see blue to green light. The reason for this is due to the light absorbing traits of water. By the time any water gets down to where this critter lives (915 to 1,830 m or 3,000 to 6,000 ft), all the red, yellow, orange, and other colors have been absorbed. This is why most bioluminescence is blueish. But the Black Dragonfish is a non-conformist and is not willing to settle with just blue. Instead the Dragonfish relies on a pair of photophores under its eyes that emit red light. With only it and a handful of other species being able to see such wavelengths of light, the Dragonfish can effectively use its photophores as targeting sensors. The red light will shine on its prey and the morsel won't even know that it has been sighted.
To emit red light, the Dragonfish has modified one of its many blue photophores. Using pigments and filters, the light is eventually modified until it is emitted at the proper wavelength of 705 nm, the far red. While this is certainly an interesting adaptation, it is nothing compared to how it actually sees the red light it emits.
Some organisms, such as the closely related genus Aristostomias, just have an extra photoreceptor pigment. But such a simple adaptation that would have been too easy for Malacosteus niger. Instead it makes its own photoreceptor. One of the many things eaten by Dragonfish are copepods. Copepods, in turn, often feed on photosynthetic bacteria. This gives the Dragonfish just the right materials to start fashioning itself spy lenses. Some of the chlorophyll from the bacteria makes its way to the eye where it settles on a photoreceptor. Here, it can absorb the rare red light and transfer the signal to the photoreceptor cells.
This was such a brilliant idea that the idea is now being experimented upon for human use. In experiments involving rabbits and mice, after being given eye-drops with the chlorophyll derivative chlorin e6, the rodents were able to see twice as well in the dark. In timer perhaps such an enhancement may be available to people.
The Bioluminescence Webpage