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Deep sea fish can detect colour in the dark

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Posted May 14, 2019

A team of international researchers has found that deep-sea fish have developed surprisingly diverse vision that enables them to detect colour in the dark.

The ground-breaking study, published in Science, found that many fish living more than 1000m below the ocean surface had extraordinary visual systems that could help them survive by being able to detect prey or avoid predators at depths where only dim light existed.

Co-author Associate Professor Wayne Davies and Dr Jessica Mountford, from UWA’s Oceans Institute and School of Biological Sciences, said the discovery shed new light on the evolution of vertebrate visual systems, including humans.

Ailver spinyfin (Diretmus argenteus) is one of those deep-ocean fish that has an enhances colour vision. Image credit: Emma Kissling via Wikimedia

“The vertebrate eye contains rod and cone photoreceptors that detect light for image-forming colour vision,” Associate Professor Davies said.

“In general, rods sense low levels of light (eg at night), whereas cones detect bright light environments such as during the day. In both cases, specific wavelengths of light are absorbed by opsin proteins – the light-sensitive molecules that are housed in rods and cones.

“In vertebrates, colour vision is mediated by cones that derive from up to four different types of opsin-based pigments that are sensitive to the visible spectrum of light, including UV. However, almost all vertebrates contain a single rod opsin pigment so would be colour-blind in conditions where there is very little light, such as the deep sea.

“At deeper depths up to 1000m or more, down-welling sunlight is filtered out to leave only faint levels of blue light – it is very much a monochromatic landscape where deep-sea fish primarily detect this single colour as a way of seeing a moving target against the background.

“However, this collaborative research team has discovered something quite spectacular.”

The research team, including scientists from UWA and lead research teams from the University of Queensland, Charles University in the Czech Republic and the University of Basel, examined the genomes of 101 species of fish, and found 13 species had more than one rod opsin gene. One species – the silver spinyfin fish – was found to have a remarkable 38 rod opsins.

“Taken together, state-of-the-art gene sequence analyses and functional experiments suggested that the silver spinyfins were able to detect a wide range of different wavelengths and are likely to sense many diverse colours,” Associate Professor Davies said.

“It is probable that this rod-based colour visual system evolved for survival against predation or to detect prey that produce bioluminescence – a form of mostly blue/green light emitted by many living organisms in the deep sea.

“The advantage of a very sensitive colour visual system would assist these remarkable fish to determine quickly whether they were seeing an unwanted predator or a potential source of food.”

Source: The University of Western Australia

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