Apparently this is a species of mackerel fish which has degenerated eyes as a result of disuse and the natural evolutionary process. For more than a thousand years the species have not had the benefit of exposure to sunlight. Hence their eyeballs have undergone atrophy through evolution and lost their visual function. This fish species is found in a dark lake within the cave of Jiu Xiang (a member of the International Cave Association) near Kunming in Yunnan.
When I visited Jiu Xiang in July 2007, I found the underground water cave to be heavily muddy and sheltered away from light. What you see in the photograph are fish that have been captured by the local marine biologists and put on public display in an aquarium. It is a species of blind mackerel and the scientific name is "Golden Thread Fish". The eyeballs are vestigial and completely covered by eyelids that are permanently glued down and that no longer retract. The local specialists name the rare species as "Mang Yu" meaning "blind fish" and have put them under provincial protection.
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