"These fish I am looking for are hiding in the depths of the mountains, not only in the depths of the mountains, but also in the depths of the caves. They are little known to us humans, living leisurely underground in the darkness..."
Listen to "Global Junior Geography" tell you the story of the blind fish in the cave.
We climbed all the way up the rough trail, but there was no way to talk about the road at all, only the occasional trace left by someone or cattle and sheep walking by. On both sides were tall bushes, and the protruding branches kept scraping the skin, clothes and backpacks. The backpack was full of caving and fishing gear, and it felt heavier and heavier now. The sound of wheezing was mixed with the sound of stones rolling down under my feet, and I sighed in this voice: an expert in the study of fish, the mountain can climb more than anyone!
At this time, the guide who was walking in front of him turned around, and with a finger of his left hand, a deep hole appeared not far away. It is in such caves that there lives the animal friend I want to visit, the cave fish.
Large-headed highland loach
Blind eyes are not blind
Five fingers are not visible in the cave, and living in such an environment for a long time, the eyes seem to become superfluous organs. Therefore, after a long period of evolution, the physical characteristics of cave fish have gradually changed, and the transformation of the visual organ is the first to bear the brunt. In a dark environment, due to the lack of light, the eye completely loses its role as a light sense and vision, so it becomes smaller and smaller, and slowly evolves into a pair of eye spots. Some types of eyes even disappear completely, and the optic nerve is basically degenerated, becoming a "blind fish" without compromise.
In fact, the degeneration and disappearance of the visual organs not only occurs in blind fish, but also in some other animals living in caves, such as the "blind shrimp" (below) and blind stove horses found in China's Guangxi Zhuang Autonomous Region.
Some organs have become more developed. Cave fish can feel a wide range of stimuli, in addition to the identification of food and the same kind, they can even determine their position through the sense of smell; the tentacles and even fins of cave fish are relatively long; the lateral line system on their bodies is more developed than that of surface fish. These evolutionary approaches can help them perceive their environment well, be flexible in avoiding danger, and live more calmly in caves. Therefore, although the eyes of some species of cavefish have been completely degraded, they have not affected their movement at all, and they are still agile in the water, which can be described as "blind and not blind".
Unknown horns
Among the cave fish distributed in China, some of the strangest places are not the disappearing eyes and translucent body, but a forward protruding horn on the top of the head, which is very rare among ordinary fish, so some people have made various speculations: some people think that this is a sensory organ; some people think that the horn plays a protective role, like the helmet used in the cave. In my brief rearing and observation of the golden herring (a class of cave fish), I found that they would hang on the wire of the temporary box with raised horn hooks, which meant that cave fish could also rely on this structure to hang their bodies and fix them in underground rivers... All kinds of claims are speculations, and the function of these horn-like structures has not yet been convincingly studied. But the similarity of the angles between different species largely reveals the kinship between species, providing us with important evidence for understanding the evolution of cave fish and the process of species differentiation.
Fork-backed gold-lined catfish
Back trimmer
Transparent elves in the dark
Because there is no need for body color to resist ultraviolet radiation, the gorgeous appearance is a luxury in the dull hole, so the body color of many cave fish gradually fades, and the body is mostly milky, flesh red, transparent or translucent, in addition, even the scales have become small and small, or even disappeared. Under the illumination of the light, these transparent creatures with subcutaneous blood vessels, bone spurs and even internal organs are faintly visible, like a strange and playful little elf swimming freely in the quiet underground river, which makes people can't help but sigh the magic of creation.
Lo cheng ling loach - the heart, intestinal tract and egg particles are clearly visible.
Cave fish in China
China is the country with the largest number of cave fish in the world, with about 130 species found and recorded in China, all of which are endemic to China. However, due to the limitations of the living environment, the number of certain species of populations is very rare. For example, the back-repairing hyacinth that we surveyed and captured in April 2014 is the second and only living specimen found in the world, and has extremely important scientific research value.
Caves and underground river systems seem to be another world, as if they are far away from our noisy society, in fact, groundwater and surface water, like surface water, are in the water circulation system, and will be affected by our production and life. The sewage discharged from villages and factories, the fertilizers and pesticides applied in farmland, on the one hand, will gradually converge in the surface rivers and drill into the ground with the flow of water; on the other hand, through the action of infiltration, it will also directly penetrate into the underground rivers. In addition, drilling and pumping, mountain quarrying, and road construction will also directly damage the cave system. China's abundant cave fish resources provide us with good scientific materials for exploring the evolution of life in extreme environments, but because the distribution areas of most species are very small, and some species are only distributed in a cave or an underground river, if this area is destroyed by humans, it will bring ruin to the species. This feature also brings great difficulties to the protection of cave fish.
How many fish without eyes and bright-eyed humans have quietly disappeared before they meet. Can this regret disappear with the discovery of cave fish? That's what I hope.
Excerpt from the March 2016 issue of Global Junior Geography
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