The only fish with eyelids is the West Australian rock cod, also known as the Western blue groper (Achoerodus gouldii).
The West Australian rock cod is a species of wrasse that is endemic to the coastal waters of southern Australia, particularly in the Western Australian region. This fish is quite large, with males growing up to a length of 1.2 meters and females growing up to 75 centimeters. The fish is commonly found in rocky reef environments and kelp beds, and is known for its striking blue-green coloration and its curious behavior towards divers.
One of the most unique features of the West Australian rock cod is its eyelids. Unlike most fish, which have a transparent third eyelid called a nictitating membrane that protects their eyes, the West Australian rock cod has two fully formed eyelids, just like humans. The eyelids are used to protect the fish’s eyes from debris and to help them sleep.
Having eyelids is a rare feature among fish, as most fish do not have fully formed eyelids like humans do. Instead, many fish have a nictitating membrane that covers their eyes and provides some level of protection. The West Australian rock cod is one of only a few species of fish that have fully formed eyelids, which has led to its status as a bit of a biological oddity.
It is believed that the West Australian rock cod evolved its eyelids as a result of its habitat. The rocky reef environments where the fish lives are often exposed to strong currents, which can kick up sand, debris, and other particles that can damage the fish’s eyes. The eyelids provide an extra layer of protection against these hazards, helping the fish to survive in its challenging environment.
In addition to its unique eyelids, the West Australian rock cod is also known for its curious and friendly behavior towards divers. It is not uncommon for the fish to swim up to divers and interact with them, which has made it a popular species for divers to encounter. The fish’s large size, striking coloration, and unusual features make it an interesting and engaging species for marine enthusiasts and scientists alike.
In conclusion, the West Australian rock cod is the only fish known to have fully formed eyelids. This unique feature is believed to have evolved as a result of the fish’s rocky reef habitat, which is exposed to strong currents and other hazards that can damage the fish’s eyes. Despite its unusual features, the West Australian rock cod is a beloved species among divers and marine enthusiasts, thanks to its friendly behavior and striking coloration.