Shrimp live in a vision-centric world. Their ocean habitat is full of colorful corals, plants, and fish. So you may wonder—with their bulbous eyes that seem to pop out of their heads, how many colors do shrimp actually see?
If you’re short on time, here’s a quick answer to your question: researchers believe shrimp likely see a range of colors across the light spectrum, perhaps even more vividly and in higher definition than humans.
In this comprehensive guide, we’ll cover everything you need to know about shrimp vision and color perception. You’ll learn about the shrimp eye structure, what colors they can detect, how their color vision compares to human sight, and why color vision matters so much to shrimp survival and communication.
Shrimp Eye Structure and Function
Cornea and Retina
Shrimp, like many other crustaceans, have compound eyes made up of thousands of small visual units called ommatidia. Each ommatidium contains a cornea, a lens, and photoreceptor cells that can detect light. The corneas in each ommatidium refract light and focus it towards the retina.
The retina contains photopigments called rhodopsins which detect different wavelengths of light. This gives shrimp the ability to see color.
Rhabdoms and Light Detection
Within each ommatidium are light-sensitive organs called rhabdoms. These contain the photopigments that allow shrimp to detect light. Shrimp have up to 16 different photopigments in their rhabdoms, allowing them to see many more colors than humans who only have 3 types of photopigments.
The rhabdoms are arranged in tiers, with each tier containing photopigments sensitive to different wavelengths. This tiered structure gives shrimp “color vision” and allows them to distinguish colors.
Lack of Spheric Lenses
One of the limitations of compound eyes is that they lack the ability to focus light that comes from different directions and distances. This is because ommatidia lack spherical lenses that can refract light and produce focused images.
Each rhabdom only points in one direction, so shrimp have a relatively poor resolution of vision. However, their compound eyes give them an extremely wide field of view of up to 360 degrees. This allows them to easily detect motion and changes in light intensity from all directions – an ability that is very important for detecting predators and prey.
Shrimp See More Colors Than Humans
Tetrachromatic Vision
Unlike humans who have trichromatic vision and can only see three primary colors (red, green and blue), shrimp have tetrachromatic vision, meaning they have four different types of color receptor cells. This allows them to see many more colors than we can imagine.
Shrimp can see ultraviolet, violet, blue, green, yellow, orange and red.
Sensitivity to Ultraviolet Light
One major difference between human and shrimp vision is that shrimp are highly sensitive to ultraviolet light. Their eyes contain special retinal pigments that allow them to see light in the ultraviolet range (300-400 nm wavelengths).
Humans cannot see UV light because our cornea and lens filters it out. For shrimp, UV sensitivity likely helps them locate food and detect predators.
Enhanced Color Intensity Detection
In addition to a wider color spectrum, shrimp may also have more vivid color perception than humans. Research suggests that the complex structure of a shrimp’s eye allows it to better distinguish slight variations in color intensity.
While humans see about 1 million different colors, shrimp may be able to detect over 30 million unique chromaticities. This hyper-spectral vision is useful for tasks like finding well-camouflaged prey or selecting the ripest fruits from vegetation.
Importance of Color Vision to Shrimp
Food Detection
The ability to detect color is critical for shrimp to locate food sources. Shrimp have specialized light-sensitive cells called photoreceptors that allow them to distinguish different wavelengths of light. This helps them identify places where algae and other nutritious matter may be found.
For example, shrimp can detect the green and brown hues of seaweed and plant matter growing on the seafloor or floating in the water column.
In addition, certain plankton and small organisms that shrimp feed on have pigments that reflect particular colors. By honing in on these color cues, shrimp can efficiently find patches of water rich in prey.
In fact, one study found that grass shrimp were most adept at detecting wavelengths of light corresponding to the peak absorption spectra of their phytoplankton food sources.
Predator Avoidance
The capacity for color vision also assists shrimp in evading predators. Shrimp have a transparent or translucent bodies, making them vulnerable to larger animals. However, their color vision allows them to better blend in with surroundings by matching the hue of plants and substrates below them.
This form of camouflage, known as countershading, works best if shrimp can accurately perceive the environment’s predominant colors and patterns.
Additionally, certain species of shrimp have evolved conspicuous color displays to warn potential predators. For instance, the peppermint shrimp has bright red bands on a white body. This aposematic coloration flags its unpalatability, signaling “stay away” to fish and other shrimp-eaters.
In order for this strategy to work, predators must also possess color vision to recognize the vivid warning signs.
Mate Attraction
Vibrant colors are not only useful as warnings – they also help shrimp locate mates. Male and female shrimp communicate their readiness to breed in part through dramatic shifts in pigmentation and coloration.
So the capacity to distinguish these visual cues is essential for initiating courtship and reproduction.
A particularly striking example is the harlequin shrimp. Usually brown or orange, the female takes on a vivid display of purple, red, and white stripes when releasing pheromones to attract males. And the receptive male responds by ramping up production of blue pigments.
This interplay of dynamically changing colors enables pairs to find each other amidst ocean waters. After mating, the pronounced colors fade away.
Differences Between Shrimp Species and Environments
Deeper Water vs Shallow Water
Shrimp that live in deeper ocean waters tend to have better vision and more complex eyes than those dwelling in shallow waters or freshwater environments. For instance, deep sea shrimp species like Heterocarpus and Pandalopsis have more advanced compound eyes, with some featuring up to 6,000 ommatidia (individual eye units) for detecting bioluminescence and other faint light cues in the deep dark waters.
These species need exceptional vision to spot food and mates. By contrast, shallow water shrimp like brown shrimp and grass shrimp have much simpler eyes, since they live in brighter, more visible habitats near the coasts and reefs.
Additionally, the make up of a shrimp’s eye depends greatly on the amount of light available in their niche environment. Species dwelling in constant darkness frequently only have a single dorsal organ to detect faint shadows and movements, rather than a full stalked eye.
Meanwhile, shrimp living in intertidally zones, like fiddler crabs, have eyes situated on mobile stalks to cope with fluctuating light conditions. So as a general rule, diminished lighting leads to advanced vision capabilities in shrimp, while consistent light breeds simpler eye structures.
Variations in Eye Structure
Not only are shrimp eyes diverse between environments, but also between species. For instance, pistol shrimp have unusually elongated eyes to spot the pistol-like claws of potential mates. Mantis shrimp eyes move independently like a chameleon and can see a staggering 12 channels of color to view polarized light and multispectral images.
Some shrimp even have regions of increased acuity in their compound eyes, acting like built-in binoculars for detecting prey and threats.
Meanwhile, lower ranking shrimp often have underdeveloped eyes as juveniles that only fully form once they mature and gain access to better niches.
But while shrimp eye designs are incredibly diverse, most structure variations serve to improve mate signaling or environmental fitness in some form. Species dwelling in tight spaces often have eyes on long stalks for greater visibility.
Shrimp in murky waters may have enlarged light receptors for better sensitivity. Predatory shrimp feature increased acuity and faster flicker fusion rates to better track attacking. So from pistol-like elongations to polarized lighting perception, structural variations in shrimp eyes serve important evolutionary functions.
Conclusion
As small crustaceans drifting through complex ocean environments, shrimp rely heavily on their vision for survival and communication. Their eyes have evolved to detect colors across an expansive range – perhaps with even greater intensity and definition than human sight.
Research suggests most shrimp species see a variety of colors including ultraviolet light. Their tetrachromatic vision helps them find food and mates, avoid danger, and generally understand the visual world around them.
