Fish see in water at night by using a combination of visual, sensory, and bioluminescent adaptations that allow them to perceive their surroundings in low-light conditions. These adaptations include larger eyes, more rod cells, a reflective layer behind the retina, a lateral line system, and interactions with light-producing organisms. In this article, we will explore how these adaptations work and why they are important for the survival and evolution of fish in the dark.
One of the most obvious adaptations that fish have for seeing in the dark is having larger eyes. Larger eyes can capture more light and have a wider field of view, which is useful for detecting movement and avoiding predators. Some examples of fish with large eyes are lanternfish, dragonfish, and flashlight fish, which inhabit the deep sea where sunlight is scarce or nonexistent.
Another visual adaptation that fish have for seeing in the dark is having more rod cells in their retina. Rod cells are photoreceptors that are sensitive to dim light and are responsible for night vision. Rod cells also have a higher density of rhodopsin, a pigment that absorbs light and converts it into electrical signals. Rod cells are more abundant in nocturnal fish, such as catfish, than in diurnal fish, such as goldfish.
A third visual adaptation that fish have for seeing in the dark is having a tapetum lucidum, a layer of reflective tissue behind the retina that enhances the light available to the rod cells. The tapetum lucidum acts like a mirror, reflecting the light that passes through the retina back to the rod cells, thereby increasing the sensitivity and brightness of the image. The tapetum lucidum is common in many deep-sea fish, such as hatchetfish, as well as some freshwater fish, such as walleye.
Apart from visual adaptations, fish also have sensory adaptations that help them navigate and locate prey or predators in the dark. One of these adaptations is the lateral line system, a series of pressure-sensitive organs that run along the sides of the fish’s body. The lateral line system allows fish to sense vibrations, currents, and changes in water pressure, which can indicate the presence and direction of other animals or objects in the water.
Another sensory adaptation that fish have for navigating in the dark is the neuromast, a type of sensory cell that is found in the lateral line system as well as on the skin, fins, and gills of some fish. The neuromast detects movement and changes in the surrounding water by using hair-like structures called cilia, which bend in response to the water flow. The neuromast can help fish accurately locate prey and escape from predators, as well as maintain balance and orientation in the water.
Bioluminescent Adaptations for Communicating in the Dark
Bioluminescence is the production and emission of light by living organisms, and it plays a significant role in the dark depths of the ocean. Many fish use bioluminescence for various purposes, such as attracting prey, luring mates, signaling to others, and camouflaging themselves. The light emitted by these fish can be perceived by other fish, enhancing communication in an environment where visual cues are limited.
Some fish produce bioluminescence by using specialized organs called photophores, which contain light-producing bacteria or chemicals. These photophores can be located on different parts of the fish’s body, such as the eyes, mouth, fins, or tail, and can be controlled by the fish to produce different patterns and colors of light. Some examples of fish that use photophores are anglerfish, viperfish, and lanternfish.
Other fish produce bioluminescence by using symbiotic relationships with light-producing bacteria or algae. These bacteria or algae live inside or on the fish’s body, and provide light in exchange for nutrients or protection. The fish can regulate the light by changing the shape or position of the bacteria or algae, or by covering them with skin or scales. Some examples of fish that use symbiosis are flashlight fish, pinecone fish, and cookie-cutter sharks.
Conclusion
Fish see in water at night by using a combination of visual, sensory, and bioluminescent adaptations that allow them to perceive their surroundings in low-light conditions. These adaptations include larger eyes, more rod cells, a reflective layer behind the retina, a lateral line system, and interactions with light-producing organisms. These adaptations are vital for the survival and evolution of fish in the dark, as they enable them to find food, avoid predators, and communicate with others. Fish are amazing creatures that have adapted to the diverse and challenging environments of the aquatic world.
