Wandering around your local aquarium, totally entranced by the many different varieties of fish and aquatic life swimming gleefully, you might begin pondering the anatomy of such interesting creatures. Fish are totally different from any animal on land, and this is clear in their DNA as well as their behavior, too. There are many unanswered questions about fish that still trouble the brains of many people to this day.
You’re bound to have considered what it’s like to be a fish, swimming through the ocean without a care in the world, but one important feature may have you stumbled.. have you ever seen a fish blink? Well, the answer is simple, and it can be found in a fish’s physical makeup.
Those who claim to have seen a fish blinking aren’t telling the truth, as fish cannot blink or close their eyes in a conventional manner, as they do not have eyelids. Eyelids are absolutely essential for blinking as they are what cover your eyes when you close them, so lacking such a key feature makes it impossible for fish to blink! Of course, this means that fish’s eyes are in constant contact with water, and they can withstand such an experience as they have adapted over many hundreds (or even thousands) of years to suit the environment in which they live.
You may be surprised to find out that the physical structure of a fish’s eye is actually very similar to our own human eye – all besides the lens. The lens is the part that sits just behind the iris and it is used to channel light toward the retina, so such an adaptation makes a dramatic difference. Such a difference is down to the fact that we as humans live in a more ‘airy’ environment, so our lenses are flat and thinner. On the other hand, a fish lives its life in the water wherein in comparison there is far less sunlight to utilize, so their lens is thicker and shaped similar to marble. If a human were to open their eyes when they go underwater everything they see would be out of focus and blurred, thus proving the significance of such a small change in the lens’s form.
It is important to note that there is all but one exception to the eyelid rule, as a single species of fish has its own form of the eyelid that allows them to close their eyes. Sharks are the only fish that can blink due to a nictitating membrane that serves as a kind of eyelid. Not all shark subspecies have the capacity to blink – for example, a great white shark does not have this membrane and instead will roll their eyes back into their head to protect themselves during the conflict, hunting, or mating.
There you have it. Fishes do not blink and cannot close their eyes, simply because they don’t need to.