Dogs can hear sounds we can’t, and many other animals can see light beyond our human “visual spectrum,” such as ultraviolet light waves to find prey or avoid becoming prey. But until now, the near infrared spectrum was considered off limits to animals.
New research led by Dr. Sebastian Baldauf from the University of Bonn reports on the first known fish with infrared vision. The study appears in the October 21 online edition of NaturWissenschaften. The fish, called Pelvicachromis taeniatus, is a native of Africa and lives in shallow, murky streams. Usually, near infrared light signals are unsuitable for seeing because of ‘signal noise’ coming from heat.
‘Physiologists thought that noise levels in the near-infrared range were too high to allow visual perception,’ Baldauf said.
Snakes can perceive prey using infrared signals, but they don’t perceive near-infrared signals, and they don’t use their eye; instead relying on a heat-sensitive pit organ that perceives long-wave infrared signals. The West African fish, however, definitely used its eyes.
To test this ability, the researchers fed fish one of their favorite prey: a freshwater shrimp that reflects ‘light’ in the near-infrared spectrum. In a dark tank in which only infrared lamps were installed, each fish was offered a choice between two groups of shrimps. The fish spent significantly more time hunting shrimp located in the near-infrared light-emitting area.
One reason why the fish might prefer near-infrared light lies in its habitat. It hunts in shallow, warm streams, where near-infrared light is scattered by plankton, suspended dirt and other non-living material. In addition, warmer temperatures can increase near-infrared transmission. These all add up to near-infrared as a near-perfect way for the fish to detect prey in warm, murky water.
It is not clear how the fish detect light signals through the other heat-generated signal noise of near-infrared waves. Now, scientists need to find out how this newly discovered use of near-infrared light occurs—how does the fish process near-infrared in the brain? Do animals use it to aid migration, or sexual selection? What genes and proteins control its use? The answers will call for mapping out a whole new system of perception in these animals.
Source: Meuthen, D., Rick, I., Thünken, T., & Baldauf, S. (2012). Visual prey detection by near-infrared cues in a fish Naturwissenschaften, 99 (12), 1063-1066 DOI: 10.1007/s00114-012-0980-7