If you've ever found yourself snorkelling or diving, you may have noticed that colour underwater appears slightly differently, why you may ask? Find out more here!
If you are a keen swimmer or diver, you might have noticed that the colours of known objects are different underwater. Everything appears slightly bluer and the deeper you go the more dissimilar the original colour will appear. In the case that you are diving below 20 meters and cut yourself, you will notice with surprise that your blood doesn’t seem red anymore, but instead looks green! These differences in colour are due to the properties of the water plus the scattering of suspended particles, which modify the light conditions underwater in comparison to the relatively stable light environment found on land.
Image courtesy of The University of Minnesota Sea Grant Program
How do fish utilise colour for their advantage?
Diving or snorkelling on a coral reef you will notice a huge variety of different colours and fishes, ranging from the most famous colourful Nemo (orange clownfish) & Dory (blue tang) to well camouflaged frogfish! These colours are not only there for make the fish pretty to the human eye but have a deeper significance.
The different patterns and colours can be used for communication and anti-predation tactics, along with food gathering, mate selection and predator avoidance. For these reason fishes developed a high variety of visual systems which allows them to be successful in their environment!
At the core of animal vision are opsin genes which allow in our case fishes, to see different colours. Opsins are proteins which can be found in the retina of an animal. Vertebrates evolved different opsins which are tuned on various wavelength of light; they can be therefore tuned to be sensitive to a red, blue, or even ultraviolet (UV) light!
Different habits and diets can influence which opsins are found on a fish retina. Fish feeding on zooplankton have usually UV opsins in their retinas which make them more successful in seeing the zooplankton in the open water. Herbivorous fishes instead have more red opsins which eases the feeding off algae.
Does it Vary from Fish to Fish?
The diet of the fish can change throughout his life from one life stage to another, which can be correlated to changes also in the visual system. For example, surgeonfish (the fish family of Dory), change their diet from zooplankton to algae. Scientists at the University of Queensland, in the Sensory Neurobiology group led by Justin Marshall, are investigating if these changes in habitat can be seen also in the visual system.
The light environment can also influence the opsins found in the retina of a fish: shallow water living fishes will have a different spectrum of opsins compared to deep sea fishes. This spectrum often matches the light availability at a certain depth.
Learning more about how coral reef fishes perceive their environment is useful especially at the dawn of frequent coral bleaching events. These could potentially lead to environmental changes which may affect the survival of these fishes.