Fish rely on their vision to navigate the aquatic environment. Fish eyes have a scotopic and photopic vision. Rod cells provide vision (scotopic) in semi-darkness, and dry cells provide them vision (photopic) in brightness. Eyes are a very sensitive and important thing for every animal.
Just as humans and other land animals depend on their eyes for movement, fish also depend on their eyes. Fish develop extraordinary adaptations to survive in aquatic environments and to improve with their other species and habitats. Fish eyes play an important role in their development.
Now, I will discuss fish eyes’ structure, functionality, and complexion.
Fish Vision
Fish eyes are finely tuned organs that have evolved through genealogy like other vertebrates mammals, amphibians, reptiles, and birds.
Fish hunt in the aquatic world and protect themselves from predatory animals through their keen eyesight. Fish lenses are usually round, but some species have exceptionally elliptical lens shapes. Interestingly, no difference was observed in the water refractive index of fish corneas in the aquatic environment.
However, the lens has to refract most of the time due to the effects of wind on the groundThe eye is considered a living optical device. Like the human eye, the fish eye comprises some components.E.g., Lens, Cornea, Iris, Retina and Optic nerve. Most species of fish have color vision due to the presence of optic nerves.
Some species can see ultraviolet colors, while others are more attracted to polarized light.
Anatomy of Fish Eyes
Sean P.Colin and Barbara-Ann Battle said in a journal article – The Fish Visual System Comparative Biochemistry and Physiology. The paper published by the Visiology journal has described The Fish Visual System in detail.
Here, the anatomical structure, Function of fish eyes and Adaptation to different aquatic environments are highlighted. Like humans, fish have a vestibulo-ocular reflex. vestibulo -ocular reflex is a reflex eye movement; when the fish moves its tail, it stabilizes visual images on the retina.
The cornea is a transparent dome-shaped part of the front of the fish eye. Surrounding the cornea is the sclera, a fibrous tissue that helps maintain the spherical shape of the eye and provides structural support. Also, a flexible and transparent structure lens is located behind the cornea to focus more light. Surrounding the lens is a pigmented structure called the Iris that controls the amount of light entering the eye by adjusting the pupil size.
The dynamic control of pupil size helps optimize visual sensitivity in different light conditions, from bright surface water to dimly lit depths. The retina is a complex layer of the eye that converts incoming light into nerve signals for processing by the brain.
The retina also contains other cell types, including bipolar cells, ganglion cells and horizontal cells, which play an important role in processing visual information before it is transmitted to the brain via the optic nerve.
Functionality of Fish Eyes
Water found below 6.5 pH is more likely to be polluted water. Usually, in such murky or contaminated water, their eyes play an essential role along with other organs. Their eyes have a remarkable ability to detect motion, which helps the fish react quickly in the brain to potential dangers and disasters.
Also, their eyes play a huge role in tracking the movement of the prey. However, some species of fish have low vision and rely primarily on color for low-light vision.
Adaptations of Fish Eyes
Fish that live in surface water below 200 meters (660ft). Their light is extremely low, which increases sensitivity to large eyes and bioluminescent signals and leads to adaptations such as sensitivity.
These adaptations help deep-sea fish identify prey and potential mates in the darkness of the ocean depths. Fish raise their heads to look above and below the water at the same time, and because of this, they look like fish with four eyes. The four-eyed fish is a fish in the Anabolpidea family.
Can Fish See In The Darkness
When I was learning to swim in childhood, I couldn’t see anything clearly underwater when I opened my eyes while diving. Then I used to wonder how the fish see under the water late at night which intrigued me.
Yes , some deep-sea fish species can see and move in complete darkness. The zone extending from (200-1000) Meter is called mesopelagic zone. This area has much less light than other areas. As a result, the fish species that live here have large eyes with large lenses due to genetic and environmental reasons.
Several fish have a specialized tapetum lucidum tissue, which reflects light and improves vision in dim environments. Just like a cat’s eyes glow in the dark. The optical properties of water also absorb different wavelengths of light to varying degrees.
Red and orange are available as visible light with longer wavelengths. Also , green and blue are available as visible light of shorter wavelengths. Because of this low wavelength visibility , the ocean bottom appears blue.
Only 45% of the solar energy absorbed by a 1 meter deep ocean remains in clear sea water. Only 16% light is present at 10m depth and only 1% at 100m depth. No light penetrates beyond 1000 meters. How much different fish species see underwater depends on this visual presence. Also in the dark , they rely on their lateral lines to detect movement and vibrations in the water.
Do Fish Sleep at Night
Yes, fishes sleep at night like humans and other animals. Also, scientists have said that most fish have regular schedules.
Fish move during the day and rest at night. Animals with eyelids can close their eyes, but fish don’t have eyelids, so they can’t close their eyes. There are also some species of fish that are most active at night and rest during the day.
At rest, their activity is slower and may show changes in body position. During sleep, fish take shelter in safe places where they feel secure from predators. The areas where they take shelter are under dense tree canopy, caves, crevices, etc. Fish are reactive when resting or sleeping, so they can sense changes in light and vibrations in the water.
How Do Fish See at Night
