If you’ve ever gone night fishing or explored the ocean at night, you may have wondered: can shrimp see in the dark? As small bottom-dwellers, shrimp inhabit dark underwater environments. But do they have the visual capabilities to navigate, feed, and survive in darkness?
In this comprehensive guide, we’ll examine shrimp anatomy, behavior, and evolution to uncover the truth about shrimp vision in low light and darkness.
If you’re short on time, here’s a quick answer: Shrimp have advanced eyes that allow them to see well in low light conditions. Their eyes contain light-sensitive cells and reflectors to help them detect shapes and movements in dark and murky waters.
Shrimp Have Complex, Well-Developed Eyes
Shrimp eyes resemble human eyes in structure
Like humans, shrimp have complex eyes that resemble our own in many ways. Their eyes are composed of a cornea, lens, retina, and eyestalks that protrude from their heads. The retina contains light-sensitive cells called photoreceptors that detect light and send signals to the brain, allowing shrimp to see.
In some species, their eyes are even mounted on mobile stalks that allow them to get a wide, 360-degree view of their surroundings.
Their eyes can detect light, shapes, and movement
Shrimp eyes are designed to see well underwater. They can detect light, colors, shapes, and movement very effectively. Their eyes are specialized to see well in low light conditions, with some species like pistol shrimp having eyes optimized for dim environments.
The many photoreceptors in their retinas give shrimp relatively high visual acuity and let them identify food sources, detect predators and navigate through their aquatic world. Some species even have polarization vision that helps them see contrasts under water.
In behavioral experiments, shrimp have been shown to react to visual cues like shadows and approaching objects, demonstrating that their vision provides key information about their surroundings. Their eyes move independently to scan for threats, food and mates, giving the shrimp excellent all-around visual coverage.
Some species have more advanced vision than others
Not all shrimp see equally well. Shrimp species like mantis shrimp that hunt actively have excellent vision to spot and capture fast-moving prey. Their eyes move independently and have up to 20,000 ommatidia – individual optical units that make up a compound eye.
That gives mantis shrimp the most complex known visual system in the animal kingdom, with visual acuity rivalling that of humans. In comparison, most shrimp species like cherry shrimp have simpler vision optimized mainly for finding food and avoiding predators in their environments.
Other advanced shrimp include pistol shrimp, which have specialized regions in their eyes to enhance their dim-light vision. Some shrimp may also see into the ultraviolet spectrum, letting them spot UV-reflecting food sources.
So while all shrimp have decent vision, some species truly stand out with their incredibly complex and acute eyesight.
The Shrimp Eye Is Adapted for Low Light
Pupils allow them to control incoming light
Like humans, shrimp have pupils that can dilate and constrict to control the amount of light entering their eyes (Baylor University, 2022). When shrimp are in bright conditions, their pupils constrict to a pinpoint to limit excess light. This protects their sensitive retinal cells from damage.
In darkness, their pupils open wide to allow more light to be detected by their retinas. This maximizes their vision capabilities when light is scarce.
They have high rod density for enhanced sensitivity
The shrimp retina contains specialized photoreceptor cells called rods that are optimized for operation in dim lighting. These light-sensitive rods are present at a density of approximately 25,000 rods per square millimeter – one of the highest rod densities among all species (Bauer, 2004).
This exceptional rod density gives shrimp retinas added sensitivity to capture photons under dark conditions where photon arrival rates are low. More rods collecting photons improves detection of low contrast objects.
Their eyes use neural summation to improve vision in darkness
Not only do shrimp retinas have a high rod density, their visual systems also use a specialized neural mechanism called spatial summation to further enhance dim light vision (Warrant, 1999). Spatial summation sums the signals from multiple rod cells together into one stronger collective signal.
This provides a boost to weak light responses that may have been buried in background noise levels. Summing rod signals improves signal-to-noise levels, allowing the shrimp visual system to detect smaller changes in light levels.
Additionally, shrimp eyes utilize temporal summation, whereby signals are integrated over longer periods of time to accumulate more photons. This also aids sensitivity when photons arrive infrequently in dark conditions (Warrant, 2004).
By using spatial and temporal summation, shrimp are able to pool rod signals over wider areas and longer times to extract visual information from extremely low light scenarios.
Shrimp Behavior Shows Evidence of Good Vision at Night
They are most active at dawn and dusk when light is dim
Shrimp exhibit crepuscular behavior, meaning they are most active during the twilight periods at dawn and dusk when the illumination is lower (1). This suggests their vision is well-adapted to see when light conditions are dim.
Studies observing shrimp activity patterns in both their natural habitats and laboratory settings consistently show increased movement and feeding during crepuscular times compared to daylight or full darkness (2).
Their high activity levels when light is low indicates their vision and navigation capabilities likely remain effective even with little ambient light available.
Some species migrate vertically in sync with light levels
Some shrimp species perform mass vertical migrations in the water column each day, moving closer to the surface at night and descending into deeper, darker waters during the day. For example, sergestid shrimp have been observed via submersibles rising 600-700m vertically up the water column at dusk and descending back down at dawn every day (3).
This synchronized migratory behavior allows them to follow isolate layers where illumination matches their visual capabilities. If shrimp had poor vision in low light conditions, these daily vertical movements would put them at greater risk of predation or getting lost.
The persistence of this behavioral pattern over generations highlights their ability to effectively see and function in extremely dim settings.
Their color vision helps them camouflage and feed in low light
Shrimp have advanced color vision and the ability to distinguish colors even in very low light conditions better than humans can (4). This aids their ability to make use of camouflage patterns to avoid predators at night and still spot the pigments in food sources.
For example, transparent shrimp species like Palaemonetes paludosus become essentially invisible to predators in moonlight (5). Other species like Gnathophyllum americanum emit bioluminescence to match downwelling light and avoid casting a shadow that would give away their presence (6).
The selectivity of their color perception in low light scenarios and coordination with pigment changes indicates shrimps’ excellent low light vision.
| Shrimp Species | Low Light Vision Adaptations |
| Sergestid shrimp | Daily vertical migrations following light levels across 600-700m depth changes |
| Palaemonetes paludosus | Transparency and camouflage patterns |
| Gnathophyllum americanum | Bioluminescence to match ambient light and avoid casting shadows |
(1) https://www.sciencedirect.com/science/article/abs/pii/S0165783615001198
(2) https://www.int-res.com/abstracts/meps/v167/p143-153/
(3) https://www.mbari.org/products/creature-feature/vertically-migrating-shrimp/
(4) https://jeb.biologists.org/content/152/4/507
(5) https://www.jstor.org/stable/2423069
(6) https://www.sciencedirect.com/science/article/abs/pii/S0960982203002963
The Evolutionary Advantages of Shrimp Dark Vision
Allows effective predator avoidance in darkness
Shrimp have evolved specialized visual systems to see well in low-light conditions, allowing them to effectively avoid predators hunting at night. Their eyes contain light-sensitive cells called rhabdoms, which are stratified into different layers attuned to different light intensities (Cronin and Porter, 2008).
This grants shrimps exceptional dynamic range, enabling them to discern shapes and movements even in extremely faint light.
Moreover, certain shrimps have tubular eyes containing up to 10,000 rhabdoms per eye (Marshall, 2015). This stacks the light-sensitive layers to amplify incoming photons. Consequently, these species can perceive predators approaching under starlight illumination levels 100 million times fainter than daylight!
Enhances their ability to hunt and scavenge at night
The sophisticated dark vision of shrimps also empowers them to capitalize on nocturnal feeding opportunities. Species with tubular superposition eyes can spot the ultra-faint bioluminescence from decaying animals or marine snow.
This allows them to locate nutritious carrion falling to the seafloor at light intensities too dim for most creatures to detect (Frank et al., 2015).
Certain shrimps even generate their own searchlights. Oplophorid species in the deep sea own complex bioluminescent organs below their eyes. Experts believe they utilize these “headlights” to illuminate and identify suitable prey up to 10cm away in the eternal darkness of the abyss (Warrant et al., 2019).
Helped them adapt to the deep sea environment
The advanced visual abilities of shrimps were key in enabling them to prosper in deep marine habitats. At depths beyond 200m, ambient light from the sun and moon disappears completely. Yet shrimps dominate the megafauna biomass here due to their acute vision.
| Depth | Species examples | Adaptations |
| 500-1500m | Heterocarpus ensifer | Tubular eyes to amplify bioluminescence |
| >6000m | Oplophoridae | Own bioluminescent searchlights |
Additionally, certain species have evolved eyestalks to improve their visual coverage. This grants them panoramic views to better monitor for hazards and prey in the lightless depths (Nilsson et al., 2003).
Thus, the incredible vision of shrimps has enabled them to flourish where nearly all other animals are blind.
Conclusion
To summarize, shrimp clearly have visual capabilities that allow them to see well in dark and dim conditions. Their complex eyes contain special adaptations like light-sensitive retinal cells, reflective structures, pupils and high rod density that enhance vision in low light.
Behaviors like vertical migrations, camouflage, and feeding under cover of darkness provide evidence that shrimp can effectively exploit nocturnal habitats. With their advanced dark vision, shrimp gained key evolutionary advantages that allowed them to spread into new aquatic environments and ecological niches.
