People see a beautiful world of colors, but what do other animals see? Some animals see a lot more than we do, but no one really knows how they use this sight.
We see what we see because our eyes have three photoreceptors, red, green and blue. The eyes of dogs only have two photoreceptors, which are green and blue. But the eyes of many birds have four photoreceptors, which are red, green, blue, and ultraviolet (UV).
It is difficult to imagine adding a UV photoreceptor, and it is even harder to imagine how invertebrates see. Butterfly eyes have five photoreceptors that let them see in ultraviolet light and help them tell the difference between two colors that look a lot alike.
Octopuses do not have colour vision but they can detect polarised light. We know that light is made up of waves when all of these waves move in the same plane. The closest humans come to seeing polarised light is by wearing polarised sunglasses.
But this is not the end of the story. Mantis shrimp vision puts everything else to shame. These marine crustaceans may be well-known for their record breaking punch (the same acceleration as a . 22 calibre bullet), but they also hold the world record for the most complex visual system.
They have up to 16 photoreceptors and can see UV, visible and polarised light. In fact, they are the only animals that can detect circularly polarized light. This is when the wave part of the light moves in a circle. They also can perceive depth with one eye and move each eye independently. Its impossible to imagine what mantis shrimp see, but incredible to think about.
Like flies, mantis shrimp have compound eyes with tens of thousands of ommatidia, which are parts that hold a group of photoreceptor cells, support cells, and pigment cells. Gonodactylids and Lysiosquillids are species with great eyesight. In the middle of their eyes, there are six rows of modified ommatidia known as the mid-band. This is where the magic happens.
Each row is specialised to detect either certain wavelengths of light or polarised light. The first four rows detect human visible light and UV light. In fact, each row contains a different receptor in the UV, giving mantis shrimp extremely good UV vision.
The ommatidia of the last two rows contain very precisely positioned, tiny hairs. This arrangement is most likely responsible for their polarisation vision.
The overall structure of the eye is intriguing too. Three parts of each eye look at the same point in space. This makes about 20% of the eye focus on a narrow strip in space and also lets them see depth with just one eye.
To create an using this strip, mantis shrimp are constantly moving their eyes and scanning the environment. The fact that the mantis shrimp can move each eye separately is helpful here because it gives it a wide field of view.
As small aquatic creatures, shrimp inhabit murky waters where light is limited. This raises an intriguing question – can shrimp see in the dark? In this in-depth guide, we’ll analyze shrimp anatomy, behavior and evolution to uncover the truth about their visual capabilities in low light and total darkness.
An Evolutionary Look at Shrimp Eyes and Vision
Shrimp have complex, highly-developed eyes that share similarities with human eyes in structure and function Their eyes contain key components like corneas, lenses, retinas and mobile eyestalks
The retinas have light-sensitive cells called photoreceptors that detect light and transmit visual signals to the brain. This allows shrimp to see shapes, colors movements and contrasts underwater.
Different species have varying levels of visual acuity. Hunting shrimp like mantis shrimp possess incredible vision rivaling humans, with up to 20,000 visual units or ommatidia per eye. Sessile shrimp like cherry shrimp have simpler vision suited for locating food and avoiding predators.
But all shrimp species are equipped with eyes adapted to see well in aquatic environments, especially dim lighting.
How Shrimp Eyes Are Optimized for Low Light
Adjustable pupils regulate incoming light
Like humans, shrimp have pupils that constrict in bright light to prevent damage and dilate in darkness to maximize visual sensitivity. This innate light control facilitates seeing in faint light.
Dense light-sensing cells boost dim light detection
Their retinas contain light-sensitive rod cells at an incredible density of 25,000 rods per square millimeter. This allows more rod receptors to capture scarce photons in dark conditions for sensitive low light vision.
Neural summation improves signal-to-noise levels
Shrimp utilize neural mechanisms like spatial and temporal summation to amplify weak visual signals in darkness. This extracts meaningful vision from miniscule photon capture rates under extremely dim illumination.
Behaviors Revealing Shrimp’s Ability to See in Low Light
Increased activity during dawn/dusk
Shrimp are most active during twilight hours when light is dimmest. This crepuscular pattern highlights their visual effectiveness and navigation at low light intensities.
Synchronized depth migrations
Some shrimp species migrate vertically up and down by hundreds of meters daily, tracking light levels optimally suited to their vision. This demonstrates excellent capabilities under a wide range of low to zero ambient light.
Dynamic camouflage and feeding
Shrimp accurately perceive colors for camouflage and detecting food sources even in moonlight. This shows their visual acuity remains attuned in darkness.
The Evolutionary Advantages of Shrimp Dark Vision
Enhanced predator avoidance
Shrimp eyes discern shapes and motion in extremely faint light, allowing effective nighttime predator detection. Their retinas contain stratified light-sensitive layers covering diverse intensities.
Some species have tubular eyes that amplify the faintest bioluminescence to see in starlight conditions 100 million times dimmer than daylight.
Improved nocturnal hunting and scavenging
Advanced dark vision empowers shrimp to capitalize on night feeding. Deep sea shrimp even generate bioluminescent searchlights to illuminate prey in perpetual darkness.
Colonization of new habitats
The sophisticated visual capabilities of shrimp enabled them to thrive in low light realms. Their eyes gave them key evolutionary advantages to spread into novel ecological niches.
Common Shrimp Tank Questions on Shrimp Vision
Do shrimp sleep at night?
Many shrimp remain active at night to feed and explore, indicating substantial dark vision. However, some daytime-active species may rest more at night. Shrimp don’t have true “sleep” but do have periods of inactivity and reduced responsiveness.
Do shrimp need light at night?
Some minimal illumination from moonlight or tank lighting can aid nighttime navigation and feeding but is not essential. Shrimp have adequate visual sensitivity to function in total darkness if needed.
Do shrimp get scared of the dark?
Shrimp show no adverse behaviors in darkness and naturally inhabit low light environments. Some species even migrate into lightless depths daily. So darkness itself likely does not frighten shrimp or deter their activity.
However, sudden large drops in light levels can startle shrimp and should be avoided. Maintaining some minimal light at night prevents this.
Should I turn off my tank light at night?
It’s generally recommended to have a consistent day/night cycle with 8-12 hours of light during the day and lights fully off at night. However, shrimp can tolerate some low level moonlight-type illumination at night if desired for viewing.
Complete darkness at night provides the most natural conditions for shrimp. But some individuals appreciate being able to observe their shrimp anytime with minimal night lights.
Do shrimp need light to breed?
Shrimp use visual cues during mating routines and require some ambient light to initiate breeding. But they can breed under moonlight or very low tank lighting at night. Complete darkness may hinder breeding. So maintaining a day/night cycle optimizes shrimp reproduction.
The Bottom Line
While shrimp prefer shaded habitats, evolution has granted them excellent nocturnal visual abilities. Their specialized eyes allow them to navigate, feed and flourish under extremely faint light where most species are rendered blind. Rather than deterring them, darkness offers shrimp unique ecological opportunities.
So next time your aquarium lights switch off, rest assured your shrimp can still see their world shrouded in blackness that resembles the eternal night of the deep oceans from where they came. Their eyes will continue to shine like tiny beacons in the dark.
I see … but what’s it for?
Many animals are known to use visual signals. Female peahens like male peacocks with more eye spots in their train, and male chameleons show they are in charge by using brighter colors. Behavioural observations and morphology suggest that mantis shrimp are using their complex visual system for communication, too.
Male mantis shrimp are known to perform courtship dances to females and aggressive displays to other males. Both behaviours show off coloured patches which vary in reflectance properties (e. g. brightness, colour) across individual mantis shrimp. This suggests that flashing these patches could provide information to the receiver about the signaller.
Despite these indications that mantis shrimp are using visual signals, the work on this topic is sparse. Circularly polarized light may be used by mantis shrimp as a way to communicate secretly and for courtship. Besides this, we know very little about visual communication in mantis shrimp.
What does the mantis shrimp see?
Can a shrimp see a different color than a human?
The results upend scientists’ suspicions that the shrimp, with 12 different types of colour photoreceptors, could see hues that humans, with just 3, could not, says study co-author Justin Marshall, a marine neuroscientist at the University of Queensland in Brisbane, Australia.
What is the black line in shrimp?
What’s that black line in shrimp? The dark line running through the backs of shrimp goes by many names—the dorsal tract, back vein, or sand vein, Tori Stivers, MS, a seafood specialist at the University of Georgia Marine Extension and Georgia Sea Grant, tells SELF. The marking is made up of the shellfish’s stomach, midgut, and intestine.
Do fish live in dark environments?
In fact, most fish are perfectly comfortable living and swimming in darker environments; rather, what they’re aggravated by is a sudden transition between light and dark. Fish rely heavily on the light to determine where they should go, what prey they can find, and how they should interact with their peers.
What is the black stuff on a shrimp?
The marking is made up of the shellfish’s stomach, midgut, and intestine. Those structures support the crustacean’s digestive process, so yes, that black stuff is the shrimp’s waste, she says. As for what you’re actually seeing there?