Several rare blind fish have been discovered in the dark underground caves of southwestern my country. The largest of these blind fish is less than 10 centimeters long, and their appearance is quite peculiar: slender, pink, and transparent bodies, revealing their spines and internal organs clearly, resembling glass fish. Through their long struggle against darkness, they have acquired new abilities; they can endure hunger, are impervious to cold, and are not bothered by heat. They can survive in water temperatures ranging from -10 to 35°C, demonstrating remarkable resilience. Blind fish have also been found in underwater caves in Yunnan, Guangxi, and Sichuan provinces of my country.
In many places around the world, various kinds of fish live in completely dark caves. For example, the cave bass of North America and the blind blimp of Cuba are well-known blind fish.
Cave bass are very small, generally only growing to 16-20 centimeters. They have black longitudinal stripes on their bodies, and their eyes are covered by skin, leaving only a trace. So how do these blind fish move? They have many small protrusions of different shapes on their heads and bodies. These protrusions function as sensors and can completely replace eyes, so even in environments that are dark all year round, they can still swim freely.
The blind blimp is quite beautiful, with a body that is pinkish-red, or sometimes bronze, covered with small black spots. It typically grows to 15 centimeters in length. In its juvenile stage, this fish has well-developed eyes, but as it matures, its eyes gradually become covered by skin, rendering it blind. At the same time, it develops many tiny, sensitive barbels on its head to serve as its eyes.
In the crevices and caves beneath rocks along the southern coast of California, a species of blind goby, only 10 centimeters long, can be found. This fish has light red, smooth, scaleless skin. As a juvenile, its small eyes possess vision, but as it grows, their eyes become hidden beneath its skin. Although blind, it is remarkably active, darting about in the dark caves, thanks to numerous membranous receptors on its head that allow it to quickly locate food.
There is another type of Mexican fish that has a pair of very endearing large, round eyes when it is young. Ichthyologists have observed and experimented on it and found that its eyes naturally and gradually degenerate during its development and growth, and it relies entirely on its skin to sense light and external stimuli.
There is an even more peculiar type of blind fish called the hagfish, which appeared after true fish emerged. It mainly lives in the waters off the Kamchatka Peninsula and is the only fish in the world that breathes through its nose. Although the hagfish's eyes are also covered by a membrane, it not only has receptors in its head, but its entire body is also covered with extrasensory cells, allowing it to accurately determine direction and distinguish objects. It can even burrow into the bodies of large fish, swallowing their internal organs, and then using its receptors to escape. Sometimes it even crawls into fishing nets to prey on the fish caught inside, and when fishermen haul in the nets, it can quickly escape. This fish has a remarkable ability to withstand hunger; it can survive for up to six months without food. The hagfish has four hearts, and why it has so many remains a mystery. Hagfish can also secrete a special mucus that can bind the surrounding seawater together, allowing predators to escape while they are confused by the mucus. Hagfish generally feed on tiny crustaceans or plankton.
