Can fish see in the dark? It is a common question that makes marine-life enthusiasts curious. You probably see fish swimming comfortably, feeding, and avoiding obstacles at night or in the dark.
But can they truly see in the darkness? The answer is nuanced. Some fish cannot see in complete darkness, but they thrive in low-light environments.
In short, fish’s night vision depends on how their eyes work, how light behaves underwater, and how different species have evolved over time. This in-depth guide explains the fish’s vision science and offers practical insights for aquarium owners.
TL;DR
- Fish cannot see in complete darkness, but many thrive in low-light environments.
- Deep-sea fish rely on bioluminescence and other senses to navigate, hunt, and avoid predators.
- The vision of the fish varies widely depending on habitat and species.
- For aquarium fish, darkness is not harmful; constant light is.
- Proper lighting improves fish health, behavior, and longevity.
How Fish Vision Works
To answer the question “Do fish see in the dark?”, we first need to understand what fish’s eyesight capabilities are. Fish’s eyes are naturally designed for underwater.
Fish’s Eye Structure: Fish eyes are similar to human eyes, designed to handle low light and underwater refraction.
Light Sensitivity: Fish’s eyes have multiple rods that make them detect light and movement even in a dim underwater environment.
Depth and Light: Light is different underwater. Sunlight diminishes the farther you go down in water. Many fish species have adapted to these changes to maintain their vision.
Fish Vision Adaptation Underwater
Fish living in low-light or dark environments have specialized adaptations to help them see. Take a look at how fish have evolved.
Specialized Eyes
Fish have photoreceptor cells, called rods and cones, in their eyes. Rods are sensitive to light and help see in the dark, while cones detect color and fine detail but need brighter light.
Fish living in darker waters have big eyes and a higher number of rod cells. These rods and cones in fish eyes have the perfect balance that makes them light-sensitive.
Lateral Line System
Fish have a lateral line system, a network of sensory organs that detects movement and vibrations in water.
So even when the visibility is low underwater, fish can navigate the water and hunt using this system.
Electroreception
Some species, like rays and sharks, rely on electroreception. They can detect the electric fields emitted by their prey.
Even if fish vision in low light is compromised, they can survive in the dark solely because of their evolution over time.
Which Fish Species Can See in the Dark?
Researchers have found that deep-sea fish have a remarkable sight that is better than that of many nocturnal creatures.
Below are the four species that have five or more genes that make them capable of seeing in the dark.
- Silver spinyfin
- Tube eye
- Glacier lanternfish
- Longwing spinyfin
These species live around 1000 to 2000 meters below sea level, and even then, they can see colors and other marine creatures.
How Fish See at Night
While fish have adapted well to low-light conditions, it is a myth that they can see in complete darkness. Vision, by definition, needs light.
However, as we discussed, fish rely on other senses to navigate the water when it is completely dark, such as smell, hearing, chemical cues, and the lateral line system.
This combination allows them to avoid predators and catch prey even when visual input is limited.
Secondly, the rod cells enable them to detect contrasts, shapes, and movement. Even faint moonlight or reflected starlight is enough for many fish species.
Nocturnal Fish Vision vs Daytime Fish Vision
| Feature | Nocturnal Fish Vision | Daytime Fish Vision |
| Primary Activity Time | Night and low-light periods | Daylight and bright conditions |
| Retinal Cell Type | Rod-dominant retinas | Cone-rich retinas |
| Light Sensitivity | Very high | Moderate to low |
| Color Vision | Very limited or absent | Well-developed color vision |
| Visual Detail | Low detail, high contrast | great detail and sharp focus |
| Motion Detection | Excellent | Moderate |
| Eye Size (Relative) | Often larger | Usually smaller |
| Best Lighting Conditions | Moonlight, starlight, dim water | Sunlit, clear water |
| Typical Habitat | Deep water, murky areas, reefs at night | Shallow, clear, sunlit water |
| Example Species | Catfish, eels, squirrelfish | Tangs, wrasses, cichlids |
Deep-sea Fish Vision: How They See
Researchers noticed that deep-sea fish do not have the genes to create cones. However, their rod cells have evolved to create multiple opsins that enable them to differentiate colors in the dark.
Scientists found a shocking discovery of 38 rod opsins in the silver spinyfish. The researchers believe that the rod cells in this fish have evolved to detect even the faintest light as well as see the green and blue colors of bioluminescent creatures.
However, this research was not tested on the fish directly. Deep-sea fish have adapted to withstand the pressure, darkness, and cold of the deep sea. Taking them out of their environment would kill them.
Instead, scientists injected the silver spinyfish’s genes into bacteria and generated rod opsins. Then they tested them for light sensitivity in the lab.
The Role of Bioluminescence
Fish living in the deepest parts of the ocean do not have access to any sunlight. They rely on bioluminescence to communicate and see.
Bioluminescence is the production of light by living beings. Fish generate light through chemical reactions or harbor bioluminescent bacteria.
These fish are so sensitive to the light that they can even survive in total darkness. For instance, anglerfish have a glowing lure to attract prey. Other fish use bioluminescence to avoid predators and communicate.
Fish Vision in Murky Water
Not all low-light environments are nocturnal or deep. The water of rivers, lakes, and even coastal areas is often cloudy or murky.
Fish in such conditions do the same as they do in dark and deep waters. Instead of relying only on their vision, they detect contrast, sense movement, and use vibration cues.
Fish Eyesight vs Human Eyesight
| Feature | Fish Eyesight | Human Eyesight |
| Environment | Underwater | Air |
| Low-Light Vision | Strong in many species | Weak |
| Rods vs Cones | Rod-dominant | Cone-dominant |
| Color Vision | Species-dependent | Strong (RGB) |
| Vision in Darkness | Limited, not absolute | Very limited |
| Motion Detection | Excellent | Moderate |
| Visual Sharpness | Lower | High |
| Underwater Vision | Naturally adapted | Poor without goggles |
Aquarium Fish Night Vision: What Owners Should Know
Many aquarists believe that turning tank lights off can leave fish disoriented. In reality, aquarium fish’s night vision is adapted to natural light cycles.
Fish do not need constant light. In fact, darkness allows them to reduce stress, rest more, and maintain natural biological rhythms.
How Light Affects Fish Behavior and Health
Understanding how light affects fish behavior is important for proper care. Constant lighting can
- Increase their aggression and stress
- Disturb their sleep-like time
- Weaken their immune response over time
The best practices include
- Providing fish with 8 to 12 hours of light every day
- Turning the lights off completely at night
- Avoiding bright room lights near the tank after dark
The Bottom Line
So, can fish see in the dark? The answer is not in complete darkness. But many fish species thrive in dim conditions because of their specialized eye structures and sensory adaptations.
Fish show remarkable ways to survive in limited light, whether through larger eyes, the lateral line system, or bioluminescence.
Whether in oceans, lakes, or aquariums, their visual systems are finely tuned to their environments.
Explore Pet Guides to learn more about interesting animal facts.
FAQs
Can Fish See in Total Darkness without any Light?
No, fish cannot see in complete darkness because vision requires light, however faint. Fish can function very well in dim conditions through rod cells and other senses, like vibration detection and smell.
Do Nocturnal Fish have Better Eyesight than Humans at Night?
Yes, many nocturnal fish see better than humans in low-light environments. Their eyes have a large concentration of light-sensitive rods, making them see in dim light better than human eyes.
Does Blue Aquarium Lighting help fish see at Night?
Blue aquarium light can help some fish see in the dark by simulating moonlight and enhancing colors. However, this light can also disrupt the fish’s rest cycle. Fish do not need night lights, and darker environments are better for them.
How does Fish Vision Change with Age?
Like other animals, fish’s vision can decline with age. They can experience lens changes and retinal degeneration. However, it varies by species and environmental conditions.
