雅思阅读 112: How Deep-Sea Fish See in the Dark

Adapted from 'How do deep-sea fish see in dark water?', Scientific American, February 2026.

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Reading Passage

Some deep-sea fish may be able to see light in a different way from most other vertebrates, according to a new study. The fish, found in the Red Sea, have what scientists describe as hybrid photoreceptors, light-sensing cells in the retina that combine elements of two distinct kinds of cells: cones and rods.

In human retinas, 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 the dark. But not all animals eyes work that way.

Scientists found the hybrid photoreceptors in larvae from three species of fish in the Red Sea, members of the hatchetfish, lanternfish and lightfish groups, all of which live in mostly dark, deep water. One of the fish, a hatchetfish, maintains these hybrid cells into adulthood.

The ocean's twilight zone is not an ideal environment for either rod or cone cells, explains Lily Fogg of the University of Basel in Switzerland, the study lead author. From a visual perspective, that is a bit of a nightmare, she says. Yet many deep-sea fish start their lives there, which raised the question: how do these tiny larvae see well enough to feed, avoid predators and survive in the murky midwater depths?

The answer lay in the back of their eyes. By examining the retinas of fish larvae, Fogg and colleagues found cells with features of both rods and cones. While hatchetfish hold onto these cells as adults, lanternfish and lightfish seem to lose them, developing only rods. The findings suggest photoreceptors do not exist as two rigid categories, rods and cones, but rather along a spectrum, Fogg says.

The findings, published in Science Advances, could add to our understanding of how sight developed in vertebrates. Similar hybrid photoreceptors have been found in other species, including jawless fishes and some reptiles and amphibians. Taken together, the evidence hints that this flexibility may be a deeply rooted feature of vertebrate vision rather than an odd exception. It is a reminder that biology is rarely as simple as we think it is, Fogg says.

Questions 1-5

Choose the correct letter, A, B, C or D.

1. What are hybrid photoreceptors? A. Cells that produce light B. Retinal cells combining features of rods and cones C. A type of lens D. Color filters
2. What do cone cells do in humans? A. See in the dark B. Detect color and detail in bright light C. Focus images D. Protect the eye
3. Which fish keeps hybrid cells into adulthood? A. Lanternfish B. Lightfish C. Hatchetfish D. All of them
4. Where were the fish found? A. The Pacific B. The Red Sea C. The Arctic D. The Indian Ocean
5. What does Fogg say about rods and cones? A. They are rigid categories B. They exist along a spectrum C. They are identical D. They only exist in humans

Questions 6-10

Do the following statements agree with the information? Write TRUE, FALSE or NOT GIVEN.

6. Rods are sensitive to low light.
7. Lanternfish keep hybrid cells as adults.
8. The twilight zone is ideal for both rods and cones.
9. Similar hybrid cells have been found in reptiles.
10. The study was published in Nature.

Questions 11-13

Complete the summary. Choose ONE WORD ONLY.

Hybrid cells combine features of rods and 11. Hatchetfish keep them as 12. The evidence suggests vertebrate vision may be more 13 than previously thought.

Answers

1. B 2. B 3. C 4. B 5. B
2. TRUE 7. FALSE 8. FALSE 9. TRUE 10. FALSE
3. cones 12. adults 13. flexible

Key Vocabulary

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