Some fish do have eyelids, but they don't close fully like human eyelids.
While many people assume fish lack eyelids entirely, the truth is more nuanced. The presence and functionality of eyelids in fish vary across different species.
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Most Fish: Most fish species lack true, movable eyelids. Their eyes are constantly exposed to the water.
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Sharks: Some sharks, like those mentioned in the reference video, do have a nictitating membrane, which acts as a partial eyelid. This membrane doesn't fully close but provides protection, especially during feeding or when the shark is potentially in danger.
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Function: Unlike human eyelids, which serve to blink, moisten the eye, and block out light, the primary function of fish eyelids (when present) is typically for physical protection of the eye.
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Why the Difference?: The need for eyelids in fish is less critical than in terrestrial animals. Fish live in an aquatic environment where their eyes are constantly bathed in water, preventing them from drying out.
In summary, while the majority of fish do not have eyelids in the same way humans do, some species, particularly sharks, possess a protective membrane that serves a similar, albeit limited, function.
