Adipose eyelid

A Fettlid is a transparent, immovable eyelid, which is found in some teleost groups and protects the eye and improves its streamlined shape. It is only on mullets from adipose tissue, but not in other fish with fat eyelids as herring, trevally and mackerel. Fat lids may cover the front and rear part of the eye and have a horizontal, elongated slot or to cover the whole eye except for a small opening in the center.