Fish can see all the colors of the rainbow, and then some

Quick Notes:

  • Find out about the biology of fish eyes.

  • Deep-sea fish aren’t blind in the darkness.

  • Fish can see more colors than humans can.

Anyone with eyes knows just how important vision can be, and that’s no different when it comes to fish eyesight. They use their eyes to navigate the waters, catch prey, and avoid becoming lunch for a larger predator. But how do fish see?

Their eyes are similar to mammal and bird eyes, which makes seeing everything in the water around them a non-problem. They also see a wide range of colors on the spectrum, some fish even being able to see more colors than the human eye such as ultraviolet.

What are fish eyes made of?

A fish’s eye is designed similarly to the eyes of most mammals and birds but their lens is more spherical. This gives them the ability to see larger, sharper images of the world around them. Their eyes have rods and cones, and light enters through the cornea, passing the pupil to hit the lens.

When light travels through the retina and into the lens, it passes through photoreceptors to determine how much or how little they see. Most fish have a “fixed pupil size,” while others have pupils that grow depending on the amount of light they’re looking at. Sharks and rays are two types of fish species that have growing pupils.

 Unsplash / David Clode

Deep-sea vision isn’t quite the same

It’s been long thought that fish living in the deepest, darkest depths of the ocean have a lesser ability to see colors. This is because of the biological make-up of the eye itself. The number of rods and cones attributed to that assumption because rods use only one opsin, allowing them to see in more dim lighting, and cones use two or more, which require lots of light.

Because fish see using rods and cones, it was assumed that it worked virtually the same as other animals with similar vision structures.

new study has proven, though, that’s just plainly not true for deep-sea fish. They see a lot more than just grayish hues. The study revealed that some deep-sea fish species have rod opsins, sometimes in surprising numbers, that allow them to let in more light no matter how deep into the ocean they are.

Fish are not colorblind

Four of the species found had astounding amounts of one specific opsin called RH1. The more genes for RH1 the fish had, the better they’d be able to see the color in the darkness. The study is all in theory though because studying these deep-sea fish up on the surface is almost impossible as the pressure often kills specimens before they have a chance to make it to the top.

Fish that live closer to the surface have plenty of sunlight to work with and because of their rods and cones, they’re able to see all the colors of the rainbow. Some fish, like the Sockeye salmon, however, can see further than the rainbow, so to speak. They’re able to see ultraviolet even though it’s wavelength shorter than violet at the end of the color spectrum.

Their superior vision helps them survive

The ocean can be a surprisingly dangerous place for its fish residents, but their abilities to see all the colors humans can see, some even more than that, have helped them adapt and survive with the changes of the ocean.

They’re able to adapt their eyes to the depths in which they live, whether it’s on the surface with the sun, or way down below where the sun can’t reach.

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