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fish training

Secret Communication

The work on UV vision was inspired by the finding that many birds display ultraviolet markings invisible to the human eye. Findings of this type brought some researchers to the realisation that the entire literature in the area of animal colouration was flawed due to its implicit assumption that the scientist’s (human) eye was a suitable surrogate for that of the animal under investigation. Conclusions that had been reached about sexual selection in birds had to be re-evaluated once it became clear that birds can see UV light and that UV signals are important cues in mate choice. When we started working on UV vision in fish, it had just been described for goldfish and first reports mentioned the presence of UV colours in various fish, suggesting the exciting possibility that, similar to birds, UV might play an important role in the lives of fishes.

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Ambon damselfish performing visual acuity tests in UV (340-390nm) and human visible (400-700nm) spectra.

For UV signals to reach the retina, they have to be transmitted by the ocular media (cornea, lens and humors), which means that an assessment of the transparency of the ocular media would reveal whether there is at least the potential for UV vision in an animal. We demonstrated that around half of 400 reef fish species (adults and larvae) have the potential for UV vision while the other half have gone to extremes to prevent UV from entering their eyes. An important finding that resulted from this analysis was that predatory fish have UV-blocking ocular media and are thus unable to see the UV signals of their potential prey. UV signals therefore belong to a ‘secret communication channel’ that allows prey fish to be conspicuous to each other without attracting the attention of their predators.

The facial patterns found on some damselfish can only be seen by animals with UV vision. Many fish predators have UV-blocking ocular media and are thus UV blind. The facial UV patterns found on Ambon damselfish code for individuals and species identity and may also contain information about fitness and hierarchical status etc.


Selected publicity

2016 Siebeck Visual Neuroethology Lab
Web design: Diana Kleine – Photos: Uli Siebeck, Maxi Eckes