Shoaling in fish is influenced by the presence of Ultra Violet light, says new research.
The olfactory system and the visual system are usually considered the main factors of importance when it comes to shoaling, but now new evidence suggests that light may also play a part.
Many fish can see light in the Ultra Violet spectrum of wavelengths, and it's previously been suggested that fish might use this as a visual cue as well.
To test the theory, scientists kept Three-spined sticklebacks, Gasterosteus aculeatus, in a test tank and presented them with two shoals of fish they could attempt to join.
One shoal was kept under normal light containing wavelengths in the UV region, while the other was kept under a special filter that blocked out UV rays.
The sticklebacks preferred to join the shoal they could see under the filter that allowed UV light through, to those they could see in the absence of UV light.
The researchers say that the sticklebacks also spent much more time near shoals in the darker environment, which they say may be a tradeoff between UV radiation and lower brightness during shoal choice.
The scientists believe that this is the first time that UV has been shown to have an influence upon shoaling in fishes.
For more information see the paper: Modarressie, R, IP Rick and TCM Bakker, 2006. UV matters in shoaling decisions. Proceedings of the Royal Society B. Biological Sciences 273: 849-854.