Why dont fish have eyelids?

Introduction: The Mystery of Fish’s Eye

Fish are fascinating creatures that inhabit various aquatic environments, ranging from freshwater streams to deep-sea trenches. However, one peculiar feature that sets them apart from other vertebrates is the absence of eyelids. The question arises: why don’t fish have eyelids? This article aims to explore the various reasons behind this phenomenon.

The Anatomy of Fish’s Eye: No Eyelids?

The anatomy of the fish’s eye is different from that of most other vertebrates. Fish have a spherical eye that is fixed in its position and cannot move independently like the human eye. Additionally, the fish’s cornea is more curved, and its lens is globular, which allows for better underwater vision. However, the most notable difference is the absence of eyelids. Fish do not have upper and lower eyelids like humans and other mammals. Instead, they have a transparent membrane called the nictitating membrane or the third eyelid. This membrane protects the eye and helps maintain its moisture.