Why do fish not have eye lids?

Question

Why do fish not have eye lids?

Answer 1

cos there eyes are constantly lubricated and cleaned?

Answer 2

They wre put in the wrong plaice!

Answer 3

That is the way they are.

Answer 4

they dont sleep

Answer 5

Some fish (maybe all?) have a transparent eyelid which moves over the eyeball periodically.

Answer 6

Fish don't have eyelashes, but they do have a lid of sorts. It doesn't work quite the same as our lids work, but rather it's a cover that slides over the eye to protect it. The fishes' eyelids are almost clear, so they can actually see through their eyelids. Neat, eh?

Answer 7

Just to add to your confusion, but perhaps to resolve some other unclarity: Indeed, there are "fishes" (plural allowed due to the plurality of species) that have eyelids. As someone poited out, some sharks have nictitating membranes, while others do not and roll their eyes backwards to protect them instead. The essential problem of your question, however, is the word "fish". For biologists, fish are not a truly monophyletic group. This is the fancy way of saying the critters usually subsumed under the category "fish" are actually not really closely related to one another. A shark is about as closely related to a gold fish as we are to a frog. What has been referred to as "fish" is usually an aquatic animal with some form of torpedo-shaped body (certain variations permitted), gills and fins. But if you take a closer look at the anatomy and genes of these animals, huge discrepancies and differences are revealed.

Eyelids in land animals largely serve the purpose of keeping the eye moist, a function not required in aquatic animals. But they also protect the eye from mechanical imapcts, and this certainly is a problem for all animals, aquatic or terrestrial, especially when they are predators. Take the shark example again: sharks often prey on large animals that in case of a struggle could injure the shark's eye. To protect itself, the shark with a nictitating membrane will close the membrane to cover the eye. Sharks lacking the membrane will roll back their eyes and thus protect their eyes with their sclera that contains cartelage. (If you ever have the chance to hold an eye ball of a shark, you will notice how stable it is and how you'd have a really, really hard time to bend it.) Elasmobranchs (sharks, skates, and rays) have eye lids (an upper and lower one) which cannot, however, cover the entire eye. The nictitating membrane can be viewed as a third eyelid that does the job.

In other "fishes," such as teleost, eyes are essentially lidless. Instead, here the eyes are covered with a translucent skin called the conunctiva.

I hope this helps.

Answer 8

They have not evolved them because they dont need them

Answer 9

they dont need to blink to keep there eyes moist cause there in water.

Answer 10

Dogfish do!

Answer 11

I think that they have a kind of membrane which can be brought into use if needed o]possibly when they sleep beause they do sleep if only for brief moments.

Answer 12

No real need for it

Answer 13

The main reason to have eyelids is to keep eyes moist. Most fish don't need this because they live in water, so there wasn't a compelling survival reason for fish to evolve eyelids. Some fish do have eyelids, though, like sharks -- they have eyelids to protect their eyes when they feed and go into an attack frenzy for food.

Answer 14

1: Tetrapods (us, mammals, reptiles, amphibians) split off from fish before eyelids had evolved.

2: The optics are different in air and water. The fish's eyes are sealed, and that works quite well underwater. It doesn't work as well in air, so lubrication and protection is needed above the surface.

Answer 15

! They have a c**p plastic surgeon

Answer 16

cause they never sleep!!! lol

Answer 17

i would have to say probably because they dont have much to block from their eyes!  hmm.... i dont know... :o) hehe

Answer 18

why do we? To clean our eyes of dust and dirt and to keep the the cornea moist. (I think).

Fish are surrounded by water so there is no need.