How do deep sea fish see in deep water? This new study may hold clues
Three species of Red Sea fish appear to rely on special “hybrid” retinal cells to see in dim environments
Maurolicus mucronatusA hatchetfish.
Some deep-sea fish may be able to see light differently from most other vertebrates, according to A new study. Fish found in the Red Sea have what the scientists behind the new study describe as “hybrid” photoreceptors – light-sensing cells in the retina that combine elements of two different types of photoreceptors, cones and rods.
In the human retina, cone cells enable us to see in bright environments, detecting color and fine detail, while rods are sensitive to low light, enabling us to see in darkness. But not all animals’ eyes work this way.
Scientists found hybrid photoreceptors in the larvae of three species of fish found in the Red Sea – members of the hatchetfish, lanternfish and lightfish groups, which live mostly in dark, deep waters. One of the fishes, the hatchetfish, retains these hybrid cells until adulthood.
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Lily Fog, a postdoctoral researcher at the University of Basel in Switzerland and lead author of the study, explains that the twilight zone of the ocean is not an ideal environment for rod or cone cells. “From a visual perspective, it’s a nightmare,” she says.
Yet many deep-sea fish often begin their lives there, which begs the question: “How do these tiny larvae see well enough to eat, avoid predators, and survive in the murky depths of deep water?” Fogg says.
The answer was hidden behind his eyes. By examining the retinas of fish larvae, Fogg and his colleagues found cells with characteristics of both rods and cones. While hatchetfish retain these cells as adults, lanternfish and lightfish lose them, developing only rods. The findings show that photoreceptors do not exist as two rigid categories – rods and cones – “but rather along a spectrum,” says Fogg.
conclusion, published in wednesday science advancementCould increase researchers’ understanding of how vision evolved in vertebrates.
Fogg says similar photoreceptors have been found in other species, including jawless fishes and some reptiles and amphibians. Overall, the evidence “indicates that this flexibility may be a deeply ingrained feature of vertebrate vision rather than a freak exception.”
“It’s a reminder that biology is rarely as simple as we think,” she says.
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