
© Wen-Sung Chung, University of Queensland, AustraliaThe tub-eye fish (Stylephorus chordatus) was found to use five different rod opsins within its eyes. The long cylindrical shape of the eyes increases light capture and also enables the fish to move them from a horizontal to a vertical position.
Contrary to expectations, some deep-water fish species see in colour, researchers have discovered.The depths of the ocean are unimaginably dark. Any remaining light from the surface is mostly blue and thus, it has long been assumed, for the denizens of the deep the world is dim, drab and monochromatic.
But now an international team of scientists have found the assumption to be wrong, after discovering that many deep-sea fish species come equipped with a range of previously unknown vision-related proteins.
Vertebrates use sight for just about everything: from foraging and avoiding being eaten by passing predators, to navigation and choosing a mate. This vision is based on two types of photoreceptor cells: rods and cones. The cells contain light-sensitive proteins called opsins, which come in several varieties.
Cones deal with bright light situations and have four kinds of opsins, while rods are more specialised for low light conditions and in 99% of vertebrates contain only one opsin type. This means that most vertebrates are near colour-blind in dim light.
It had been long thought that deep sea fish, living between 200 and 1500 metres below the surface, were in the same situation.
Research
published in the journal
Science reveals some remarkable exceptions.
Comment: Here is another video after the bear reached the bottom of the cliff: